The heat shock response is a conserved mechanism that plays a critical role in organismal survival under thermal stress. Caenorhabditis briggsae is a widely used model organism for comparative studies involving its well-known cousin C. elegans and exhibits increased thermotolerance under heat stress. In C. elegans, the transcription factor HSF-1 has been well characterized for its role in many processes including development, thermotolerance, and lifespan. We recently showed that Cbr-hsf-1 is necessary for fertility and protection against heat stress. Here, we report that Cbr-hsf-1 also plays essential roles during development and adulthood to maintain the lifespan of animals.
","acknowledgements":"","authors":[{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","formalAnalysis","investigation","methodology","writing_originalDraft"],"email":"bhullh2@mcmaster.ca","firstName":"Harvir","lastName":"Bhullar","submittingAuthor":true,"correspondingAuthor":true,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","formalAnalysis"],"email":"diasj8@mcmaster.ca","firstName":"Jordan","lastName":"Dias","submittingAuthor":false,"correspondingAuthor":false,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","formalAnalysis"],"email":"pastagik@mcmaster.ca","firstName":"Khushi","lastName":"Pastagia","submittingAuthor":false,"correspondingAuthor":false,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","methodology","formalAnalysis","investigation"],"email":"vandew1@mcmaster.ca","firstName":"Wouter","lastName":"van den Berg","submittingAuthor":false,"correspondingAuthor":false,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["conceptualization","fundingAcquisition","methodology","project","resources","supervision","writing_reviewEditing"],"email":"guptab@mcmaster.ca","firstName":"Bhagwati P","lastName":"Gupta","submittingAuthor":false,"correspondingAuthor":true,"equalContribution":false,"WBId":null,"orcid":"0000-0001-8572-7054"}],"awards":[],"conflictsOfInterest":"The authors declare that there are no conflicts of interest present.
","dataTable":{"url":null},"extendedData":[],"funding":"Supported by Natural Sciences and Engineering Research Council (Canada) to Bhagwati P Gupta.
","image":{"url":"https://portal.micropublication.org/uploads/06575da9b82f8927935306e84f6135ae.png"},"imageCaption":"(A) Schematic of RNAi treatment timelines used for lifespan assays. RNAi was administered from (B) embryogenesis to Day 1 adulthood at 20 °C, (C) from embryogenesis to Day 1 adulthood at 30 °C, and (D) from Day 1 adulthood onward at 20 °C. Survival curves compare Cbr-hsf-1(RNAi) worms to control (L4440) worms and were analyzed using Kaplan-Meier analysis. Statistical significance was assessed using the log-rank (Mantel-Cox) test. (E) Summary table of lifespan metrics, including median survival, maximum survival, and sample size (n) for each condition. (F-G) Normalized transcript counts of hsf-1 across development in (F) C. briggsae and (G) C. elegans. Dots represent mean values of biological replicates. The Y axis is displayed on a log scale. (H) Survival of Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms following heat stress exposure (8 and 10 hours) Statistical significance was assessed using the Mann-Whitney test. Bars represent mean percent survival ± SD. Total n = 140-154 per RNAi condition. (I) Survival of Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms following 24 hour ER stress exposure. Statistical significance was assessed using Wilcoxon matched-pairs signed-rank test. Bars represent mean percent survival ± SD. Total n = 304-347 per RNAi condition. Dots on bar graphs represent individual biological batches. For lifespan assays (B-D), 6-8 biological batches were performed per condition. For stress survival assays (H,I), 3-6 biological batches were performed per condition. Asterisks indicate statistically significant differences (**** p < 0.0001).
","imageTitle":"Survival and stress response of C. briggsae following hsf-1 RNAi knockdown
","methods":"RNAi
Worms were cultured on nematode growth medium (NGM) agar plates seeded with Escherichia coli OP50 using standard methods. An RNAi-sensitive C. briggsae strain (JU1018) expressing the C. elegans sid-2 transgene was used for all experiments (Seetharaman, et al. 2010). RNAi was performed by feeding E. coli HT115 bacteria to worms that carried double-stranded RNA targeting Cbr-hsf-1. The bacteria containing an empty vector (L4440) served as controls in RNAi experiments.
Lifespan
Embryos were obtained by allowing gravid JU1018 adults to lay eggs for 2-3 hours on the appropriate plates. For developmental knockdown, worms were exposed to RNAi from the embryonic stage and maintained at either 20 °C or 30 °C until Day 1 of adulthood, after which they were transferred to OP50-seeded NGM plates and maintained at 20 °C. For adult-specific knockdown, worms were grown on OP50 plates until Day 1 of adulthood and then transferred to RNAi plates, remaining at 20 °C for the duration of the experiment. Animals were scored for survival every 1-2 days by gentle prodding with a platinum wire; and those unresponsive to prodding were scored as dead. Worms were transferred to fresh plates as needed.
Stress assays
Synchronized populations were generated by allowing gravid JU1018 adults to lay eggs for 2 hours on OP50 seeded NGM plates. Adults were removed after egg laying, and progeny were maintained at 20 °C until Day 1 of adulthood.
For heat shock, Day 1 adult worms treated with Cbr-hsf-1 RNAi or control were transferred to OP50 seeded plates and exposed to 35 °C for 8 or 10 hours. Worms were then returned to 20 °C and allowed to recover for 24 hours before survival was assessed.
For ER stress, Day 1 adult worms were exposed to 50 ng/µL tunicamycin in 24 well plates for 24 hours. Following exposure, worms were scored for survival; animals unresponsive to touch and exhibiting a rigid, rod-like morphology were classified as dead.
hsf-1 expression
Gene expression data for C. briggsae and C. elegans were obtained from published datasets and processed using RNA STAR for alignment and featureCounts for quantification (Schmeisser, et al. 2013; van den Berg and Gupta 2025). Counts were averaged across biological replicates for each time point (C. briggsae: days 1, 3, 6, 9; C. elegans: days 1, 5, 10 of adulthood) and plotted.
Statistical analysis
All statistical analyses and figure generation were performed using GraphPad Prism (version 10.6.1). Statistical tests are indicated in the corresponding figure legends.
","reagents":"","patternDescription":"The nematode C. briggsae is commonly used in comparative biological studies alongside its close relative C. elegans. We and others have shown that C. briggsae exhibits increased thermotolerance relative to C. elegans, suggesting that these two species may differ in the mechanisms that regulate stress resistance at elevated temperatures (Felix and Duveau 2012; Jhaveri, et al. 2025; Prasad, et al. 2011).
In C. elegans, the heat shock response is regulated by the transcription factor HSF-1, whose function has been extensively characterized (Morton and Lamitina 2013). Two well described hsf-1 mutant alleles (ok600 and sy441) highlight the essential role of the gene in development and stress regulation. Strong loss of hsf-1 function (ok600) causes severe developmental defects that include arrest at the L2-L3 larval stages (Morton and Lamitina 2013). The partial loss-of-function allele (sy441) and RNAi-mediated knockdown have revealed additional roles in lifespan regulation and stress physiology (Garigan, et al. 2002; Hajdu-Cronin, et al. 2004; Hsu, et al. 2003; Morley and Morimoto 2004; Morton and Lamitina 2013; Volovik, et al. 2012).
Studies on HSF-1 role in C. elegans thermotolerance have reported variable results, which may be in part due to context-dependent contribution of the gene to stress resistance. Depending on the age of the animals, the extent of HSF-1 depletion, and assay conditions used, reduced HSF-1 activity has been reported to lower thermotolerance (Finger, et al. 2021; Prahlad, et al. 2008; Steinkraus, et al. 2008), enhance thermotolerance (Golden, et al. 2020), have no effect (Kourtis, et al. 2012; McColl, et al. 2010), reduce thermotolerance after heat pre-treatment (Kourtis, et al. 2012; McColl, et al. 2010), or even enhance survival in young adults immediately after heat shock, with thermotolerance declining with age (Kovacs, et al. 2024). Recent studies have also linked HSF-1 to Endoplasmic reticulum (ER) stress responses and survival on tunicamycin, indicating its function extends beyond the canonical heat shock response (Ahmed, et al. 2026; Alcala, et al. 2026; Kovacs, et al. 2024). Together, these findings raised the question of whether the C. briggsae hsf-1 ortholog, Cbr-hsf-1 plays similar roles in C. briggsae. We recently found that RNAi knockdown of Cbr-hsf-1 from embryogenesis to adulthood caused no obvious phenotype at 20 °C but resulted in sterility at 30 °C, indicating a temperature-sensitive requirement for Cbr-hsf-1 function (Jhaveri, et al. 2025).
To further investigate the role of Cbr-hsf-1, we performed lifespan assays following RNAi-mediated knockdown initiated either during development or at the first day of adulthood. Developmental knockdown of Cbr-hsf-1 at 20 °C significantly reduced the lifespan (median 12 days, mean 11.6 days, mean lifespan 27% lower than controls), whereas the maximum lifespan was not significantly altered (Figure 1B, E). These findings indicate that Cbr-hsf-1 contributes to lifespan maintenance under non-stress conditions.
The phenotype was similar at 30 °C, although control animals also exhibited a shorter lifespan (Figure 1C, E). Notably, the proportional reduction in lifespan was similar at 20 °C and 30 °C (mean lifespan 27% lower and 24% lower than controls, respectively), indicating a lack of further reduction in Cbr-hsf-1 function at higher temperature.
To assess the post-developmental requirements of Cbr-hsf-1, RNAi was initiated at Day 1 of adulthood. Adult-specific knockdown also significantly shortened the lifespan and reduced the maximum lifespan (Figure 1D, E), indicating that Cbr-hsf-1 is needed during adult stage for normal lifespan maintenance. Consistent with this interpretation, hsf-1 continues to be expressed during adulthood in both C. briggsae and C. elegans (Figure 1F, G).
We next assessed Cbr-hsf-1's contribution to acute stress resistance. Following heat shock at 35°C for 8hrs or 10hrs, or after 24 hrs exposure to tunicamycin, Cbr-hsf-1(RNAi) animals exhibited survival comparable to controls (Figure 1H, I), suggesting that Cbr-hsf-1 knockdown under these assay conditions had no detectable effect on survival after acute heat or ER stress.
Together, these data show that Cbr-hsf-1 plays an important role in lifespan maintenance in C. briggsae, while having little or no detectable contribution to survival in the acute stress assays tested here.
","references":[{"reference":"Ahmed S, Kovács Dn, Kovács Mr, Kosztelnik Mn, Hotzi B, Sigmond Tm, et al., Barna. 2026. Heat shock factor-1 alleviates ER-stress in Caenorhabditis elegans. Scientific Reports 16: 10.1038/s41598-026-43060-3.
","pubmedId":"","doi":"10.1038/s41598-026-43060-3"},{"reference":"Alcala A, Castro Torres T, Aviles Barahona R, Frankino PA, Higuchi-Sanabria R, Garcia G. 2026. A non-canonical role for UPR\n ER\n during heat stress in\n C. elegans. : 10.64898/2026.01.08.698479.
","pubmedId":"","doi":" 10.64898/2026.01.08.698479"},{"reference":"Félix MA, Duveau F. 2012. Population dynamics and habitat sharing of natural populations of Caenorhabditis elegans and C. briggsae. BMC Biology 10: 10.1186/1741-7007-10-59.
","pubmedId":"","doi":"10.1186/1741-7007-10-59"},{"reference":"Finger F, Ottens F, Hoppe T. 2021. The Argonaute Proteins ALG-1 and ALG-2 Are Linked to Stress Resistance and Proteostasis. MicroPubl Biol 2021: 10.17912/micropub.biology.000457.
","pubmedId":"34723149","doi":"10.17912/micropub.biology.000457"},{"reference":"Garigan D, Hsu AL, Fraser AG, Kamath RS, Ahringer J, Kenyon C. 2002. Genetic Analysis of Tissue Aging in Caenorhabditis elegans: A Role for Heat-Shock Factor and Bacterial Proliferation. Genetics 161: 1101-1112.
","pubmedId":"","doi":"10.1093/genetics/161.3.1101"},{"reference":"Golden NL, Plagens RN, Kim Guisbert KS, Guisbert E. 2020. Standardized Methods for Measuring Induction of the Heat Shock Response in <em>Caenorhabditis elegans</em>. Journal of Visualized Experiments : 10.3791/61030.
","pubmedId":"","doi":"10.3791/61030"},{"reference":"Hajdu-Cronin YM, Chen WJ, Sternberg PW. 2004. The L-type cyclin CYL-1 and the heat-shock-factor HSF-1 are required for heat-shock-induced protein expression in Caenorhabditis elegans. Genetics 168(4): 1937-49.
","pubmedId":"15611166","doi":""},{"reference":"Hsu AL, Murphy CT, Kenyon C. 2003. Regulation of Aging and Age-Related Disease by DAF-16 and Heat-Shock Factor. Science 300: 1142-1145.
","pubmedId":"","doi":"10.1126/science.1083701"},{"reference":"Jhaveri N, Bhullar H, Sternberg PW, Gupta BP. 2025. Heat tolerance and genetic adaptations in Caenorhabditis briggsae: insights from comparative studies with Caenorhabditis elegans. GENETICS 230: 10.1093/genetics/iyaf061.
","pubmedId":"","doi":"10.1093/genetics/iyaf061"},{"reference":"Kourtis N, Nikoletopoulou V, Tavernarakis N. 2012. Small heat-shock proteins protect from heat-stroke-associated neurodegeneration. Nature 490: 213-218.
","pubmedId":"","doi":"10.1038/nature11417"},{"reference":"Kovács Dn, Biró JnBs, Ahmed S, Kovács Mr, Sigmond Tm, Hotzi B, et al., Barna. 2024. Age‐dependent heat shock hormesis to
McColl G, Rogers AN, Alavez S, Hubbard AE, Melov S, Link CD, et al., Lithgow. 2010. Insulin-like Signaling Determines Survival during Stress via Posttranscriptional Mechanisms in C. elegans. Cell Metabolism 12: 260-272.
","pubmedId":"","doi":"10.1016/j.cmet.2010.08.004"},{"reference":"Morley JF, Morimoto RI. 2004. Regulation of Longevity inCaenorhabditis elegansby Heat Shock Factor and Molecular Chaperones. Molecular Biology of the Cell 15: 657-664.
","pubmedId":"","doi":"10.1091/mbc.e03-07-0532"},{"reference":"Morton EA, Lamitina T. 2012. Caenorhabditis elegans
Prahlad V, Cornelius T, Morimoto RI. 2008. Regulation of the Cellular Heat Shock Response in\n Caenorhabditis elegans\n by Thermosensory Neurons. Science 320: 811-814.
","pubmedId":"","doi":"10.1126/science.1156093"},{"reference":"Prasad A, Croydon-Sugarman MJF, Murray RL, Cutter AD. 2010. TEMPERATURE-DEPENDENT FECUNDITY ASSOCIATES WITH LATITUDE IN CAENORHABDITIS BRIGGSAE. Evolution 65: 52-63.
","pubmedId":"","doi":"10.1111/j.1558-5646.2010.01110.x"},{"reference":"Schmeisser S, Priebe S, Groth M, Monajembashi S, Hemmerich P, Guthke R, Platzer M, Ristow M. 2013. Neuronal ROS signaling rather than AMPK/sirtuin-mediated energy sensing links dietary restriction to lifespan extension. Molecular Metabolism 2: 92-102.
","pubmedId":"","doi":"10.1016/j.molmet.2013.02.002"},{"reference":"Seetharaman A, Cumbo P, Bojanala N, Gupta BP. 2010. Conserved mechanism of Wnt signaling function in the specification of vulval precursor fates in C. elegans and C. briggsae. Developmental Biology 346: 128-139.
","pubmedId":"","doi":"10.1016/j.ydbio.2010.07.003"},{"reference":"Steinkraus KA, Smith ED, Davis C, Carr D, Pendergrass WR, Sutphin GL, Kennedy BK, Kaeberlein M. 2008. Dietary restriction suppresses proteotoxicity and enhances longevity by an\n hsf‐1\n ‐dependent mechanism in\n Caenorhabditis elegans. Aging Cell 7: 394-404.
","pubmedId":"","doi":"10.1111/j.1474-9726.2008.00385.x"},{"reference":"van den Berg W, Gupta BP. 2025. Genome-Wide Temporal Gene Expression Reveals a Post-Reproductive Shift in the Nematode Caenorhabditis briggsae. Genome Biology and Evolution 17: 10.1093/gbe/evaf057.
","pubmedId":"","doi":"10.1093/gbe/evaf057"},{"reference":"Volovik Y, Maman M, Dubnikov T, Bejerano‐Sagie M, Joyce D, Kapernick EA, Cohen E, Dillin A. 2012. Temporal requirements of heat shock factor‐1 for longevity assurance. Aging Cell 11: 491-499.
","pubmedId":"","doi":"10.1111/j.1474-9726.2012.00811.x"}],"title":"The heat shock factor Cbr-HSF-1 is necessary for lifespan maintenance in C. briggsae
","reviews":[],"curatorReviews":[{"curator":{"displayName":"Gary Craig Schindelman"},"openAcknowledgement":false,"submitted":null}]},{"id":"9ce0ecf9-0ad0-4a08-a38f-3d63b79c060b","decision":"revise","abstract":"The heat shock response is a conserved mechanism that plays a critical role in organismal survival under thermal stress. Caenorhabditis briggsae is a widely used model organism for comparative studies involving its well-known cousin C. elegans and exhibits increased thermotolerance under heat stress. In C. elegans, the transcription factor HSF-1 has been well characterized for its role in many processes including development, thermotolerance, and lifespan. We recently showed that Cbr-hsf-1 is necessary for fertility and protection against heat stress. Here, we report that Cbr-hsf-1 also plays essential roles during development and adulthood to maintain the lifespan of animals.
","acknowledgements":"","authors":[{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","formalAnalysis","investigation","methodology","writing_originalDraft"],"email":"bhullh2@mcmaster.ca","firstName":"Harvir","lastName":"Bhullar","submittingAuthor":true,"correspondingAuthor":true,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","formalAnalysis"],"email":"diasj8@mcmaster.ca","firstName":"Jordan","lastName":"Dias","submittingAuthor":false,"correspondingAuthor":false,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","formalAnalysis"],"email":"pastagik@mcmaster.ca","firstName":"Khushi","lastName":"Pastagia","submittingAuthor":false,"correspondingAuthor":false,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","methodology","formalAnalysis","investigation"],"email":"vandew1@mcmaster.ca","firstName":"Wouter","lastName":"van den Berg","submittingAuthor":false,"correspondingAuthor":false,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["conceptualization","fundingAcquisition","methodology","project","resources","supervision","writing_reviewEditing"],"email":"guptab@mcmaster.ca","firstName":"Bhagwati P","lastName":"Gupta","submittingAuthor":false,"correspondingAuthor":true,"equalContribution":false,"WBId":null,"orcid":"0000-0001-8572-7054"}],"awards":[],"conflictsOfInterest":"The authors declare that there are no conflicts of interest present.
","dataTable":{"url":null},"extendedData":[],"funding":"Supported by Natural Sciences and Engineering Research Council (Canada) to Bhagwati P Gupta.
","image":{"url":"https://portal.micropublication.org/uploads/b357223fad5a0bac497a7ac79f2514a3.png"},"imageCaption":"(A) Schematic of RNAi treatment timelines used for lifespan assays. RNAi was administered from (B) embryogenesis to Day 1 adulthood at 20 °C, (C) from embryogenesis to Day 1 adulthood at 30 °C, and (D) from Day 1 adulthood onward at 20 °C. Survival curves compare Cbr-hsf-1(RNAi) worms to control (L4440) worms and were analyzed using Kaplan-Meier analysis. Statistical significance was assessed using the log-rank (Mantel-Cox) test. (E) Summary table of lifespan metrics, including median survival, maximum survival, and sample size (n) for each condition. (F-G) Normalized transcript counts of hsf-1 across development in (F) C. briggsae and (G) C. elegans. Dots represent mean values of biological replicates. The Y axis is displayed on a log scale. (H) Survival of Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms following heat stress exposure (8 and 10 hours) Statistical significance was assessed using the Mann-Whitney test. Bars represent mean percent survival ± SD. Total n = 140-154 per RNAi condition. (I) Survival of Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms following 24 hour ER stress exposure. Statistical significance was assessed using Wilcoxon matched-pairs signed-rank test. Bars represent mean percent survival ± SD. Total n = 304-347 per RNAi condition. Dots on bar graphs represent individual biological batches. For lifespan assays (B-D), 6-8 biological batches were performed per condition. For stress survival assays (H,I), 3-6 biological batches were performed per condition. Asterisks indicate statistically significant differences (**** p < 0.0001).
","imageTitle":"Survival and stress response of C. briggsae following hsf-1 RNAi knockdown
","methods":"RNAi
Worms were cultured on nematode growth medium (NGM) agar plates seeded with Escherichia coli OP50 using standard methods. An RNAi-sensitive C. briggsae strain (JU1018) expressing the C. elegans sid-2 transgene was used for all experiments (Seetharaman, et al. 2010). RNAi was performed by feeding E. coli HT115 bacteria to worms that carried double-stranded RNA targeting Cbr-hsf-1. The bacteria containing an empty vector (L4440) served as controls in RNAi experiments.
Lifespan
Embryos were obtained by allowing gravid JU1018 adults to lay eggs for 2-3 hours on the appropriate plates. For developmental knockdown, worms were exposed to RNAi from the embryonic stage and maintained at either 20 °C or 30 °C until Day 1 of adulthood, after which they were transferred to OP50-seeded NGM plates and maintained at 20 °C. For adult-specific knockdown, worms were grown on OP50 plates until Day 1 of adulthood and then transferred to RNAi plates, remaining at 20 °C for the duration of the experiment. Animals were scored for survival every 1-2 days by gentle prodding with a platinum wire; and those unresponsive to prodding were scored as dead. Worms were transferred to fresh plates as needed.
Stress assays
Synchronized populations were generated by allowing gravid JU1018 adults to lay eggs for 2 hours on OP50 seeded NGM plates. Adults were removed after egg laying, and progeny were maintained at 20 °C until Day 1 of adulthood.
For heat shock, Day 1 adult worms treated with Cbr-hsf-1 RNAi or control were transferred to OP50 seeded plates and exposed to 35 °C for 8 or 10 hours. Worms were then returned to 20 °C and allowed to recover for 24 hours before survival was assessed.
For ER stress, Day 1 adult worms were exposed to 50 ng/µL tunicamycin in 24 well plates for 24 hours. Following exposure, worms were scored for survival; animals unresponsive to touch and exhibiting a rigid, rod-like morphology were classified as dead.
hsf-1 expression
Gene expression data for C. briggsae and C. elegans were obtained from published datasets and processed using RNA STAR for alignment and featureCounts for quantification (Schmeisser, et al. 2013; van den Berg and Gupta 2025). Counts were averaged across biological replicates for each time point (C. briggsae: days 1, 3, 6, 9; C. elegans: days 1, 5, 10 of adulthood) and plotted.
Statistical analysis
All statistical analyses and figure generation were performed using GraphPad Prism (version 10.6.1). Statistical tests are indicated in the corresponding figure legends.
","reagents":"","patternDescription":"The nematode C. briggsae is commonly used in comparative biological studies alongside its close relative C. elegans. We and others have shown that C. briggsae exhibits increased thermotolerance relative to C. elegans, suggesting that these two species may differ in the mechanisms that regulate stress resistance at elevated temperatures (Felix and Duveau 2012; Jhaveri, et al. 2025; Prasad, et al. 2011).
In C. elegans, the heat shock response is regulated by the transcription factor HSF-1, whose function has been extensively characterized (Morton and Lamitina 2013). Two well described hsf-1 mutant alleles (ok600 and sy441) highlight the essential role of the gene in development and stress regulation. Strong loss of hsf-1 function (ok600) causes severe developmental defects that include arrest at the L2-L3 larval stages (Morton and Lamitina 2013). The partial loss-of-function allele (sy441) and RNAi-mediated knockdown have revealed additional roles in lifespan regulation and stress physiology (Garigan, et al. 2002; Hajdu-Cronin, et al. 2004; Hsu, et al. 2003; Morley and Morimoto 2004; Morton and Lamitina 2013; Volovik, et al. 2012).
Studies on HSF-1 role in C. elegans thermotolerance have reported variable results, which may be in part due to context-dependent contribution of the gene to stress resistance. Depending on the age of the animals, the extent of HSF-1 depletion, and assay conditions used, reduced HSF-1 activity has been reported to lower thermotolerance (Finger, et al. 2021; Prahlad, et al. 2008; Steinkraus, et al. 2008), enhance thermotolerance (Golden, et al. 2020), have no effect (Kourtis, et al. 2012; McColl, et al. 2010), reduce thermotolerance after heat pre-treatment (Kourtis, et al. 2012; McColl, et al. 2010), or even enhance survival in young adults immediately after heat shock, with thermotolerance declining with age (Kovacs, et al. 2024). Recent studies have also linked HSF-1 to Endoplasmic reticulum (ER) stress responses and survival on tunicamycin, indicating its function extends beyond the canonical heat shock response (Ahmed, et al. 2026; Alcala, et al. 2026; Kovacs, et al. 2024). Together, these findings raised the question of whether the C. briggsae hsf-1 ortholog, Cbr-hsf-1 plays similar roles in C. briggsae. We recently found that RNAi knockdown of Cbr-hsf-1 from embryogenesis to adulthood caused no obvious phenotype at 20 °C but resulted in sterility at 30 °C, indicating a temperature-sensitive requirement for Cbr-hsf-1 function (Jhaveri, et al. 2025).
To further investigate the role of Cbr-hsf-1, we performed lifespan assays following RNAi-mediated knockdown initiated either during development or at the first day of adulthood. Developmental knockdown of Cbr-hsf-1 at 20 °C significantly reduced the lifespan (median 12 days, mean 11.6 days, mean lifespan 27% lower than controls), whereas the maximum lifespan was not significantly altered (Figure 1B, E). These findings indicate that Cbr-hsf-1 contributes to lifespan maintenance under non-stress conditions.
The phenotype was similar at 30 °C, although control animals also exhibited a shorter lifespan (Figure 1C, E). Notably, the proportional reduction in lifespan was similar at 20 °C and 30 °C (mean lifespan 27% lower and 24% lower than controls, respectively), indicating a lack of further reduction in Cbr-hsf-1 function at higher temperature.
To assess the post-developmental requirements of Cbr-hsf-1, RNAi was initiated at Day 1 of adulthood. Adult-specific knockdown also significantly shortened the lifespan and reduced the maximum lifespan (Figure 1D, E), indicating that Cbr-hsf-1 is needed during adult stage for normal lifespan maintenance. Consistent with this interpretation, hsf-1 continues to be expressed during adulthood in both C. briggsae and C. elegans (Figure 1F, G).
We next assessed Cbr-hsf-1's contribution to acute stress resistance. Following heat shock at 35°C for 8hrs or 10hrs, or after 24 hrs exposure to tunicamycin, Cbr-hsf-1(RNAi) animals exhibited survival comparable to controls (Figure 1H, I), suggesting that Cbr-hsf-1 knockdown under these assay conditions had no detectable effect on survival after acute heat or ER stress.
Together, these data show that Cbr-hsf-1 plays an important role in lifespan maintenance in C. briggsae, while having little or no detectable contribution to survival in the acute stress assays tested here.
","references":[{"reference":"Ahmed S, Kovács Dn, Kovács Mr, Kosztelnik Mn, Hotzi B, Sigmond Tm, et al., Barna. 2026. Heat shock factor-1 alleviates ER-stress in Caenorhabditis elegans. Scientific Reports 16: 10.1038/s41598-026-43060-3.
","pubmedId":"","doi":"10.1038/s41598-026-43060-3"},{"reference":"Alcala A, Castro Torres T, Aviles Barahona R, Frankino PA, Higuchi-Sanabria R, Garcia G. 2026. A non-canonical role for UPR\n ER\n during heat stress in\n C. elegans. : 10.64898/2026.01.08.698479.
","pubmedId":"","doi":" 10.64898/2026.01.08.698479"},{"reference":"Félix MA, Duveau F. 2012. Population dynamics and habitat sharing of natural populations of Caenorhabditis elegans and C. briggsae. BMC Biology 10: 10.1186/1741-7007-10-59.
","pubmedId":"","doi":"10.1186/1741-7007-10-59"},{"reference":"Finger F, Ottens F, Hoppe T. 2021. The Argonaute Proteins ALG-1 and ALG-2 Are Linked to Stress Resistance and Proteostasis. MicroPubl Biol 2021: 10.17912/micropub.biology.000457.
","pubmedId":"34723149","doi":"10.17912/micropub.biology.000457"},{"reference":"Garigan D, Hsu AL, Fraser AG, Kamath RS, Ahringer J, Kenyon C. 2002. Genetic Analysis of Tissue Aging in Caenorhabditis elegans: A Role for Heat-Shock Factor and Bacterial Proliferation. Genetics 161: 1101-1112.
","pubmedId":"","doi":"10.1093/genetics/161.3.1101"},{"reference":"Golden NL, Plagens RN, Kim Guisbert KS, Guisbert E. 2020. Standardized Methods for Measuring Induction of the Heat Shock Response in <em>Caenorhabditis elegans</em>. Journal of Visualized Experiments : 10.3791/61030.
","pubmedId":"","doi":"10.3791/61030"},{"reference":"Hajdu-Cronin YM, Chen WJ, Sternberg PW. 2004. The L-type cyclin CYL-1 and the heat-shock-factor HSF-1 are required for heat-shock-induced protein expression in Caenorhabditis elegans. Genetics 168(4): 1937-49.
","pubmedId":"15611166","doi":""},{"reference":"Hsu AL, Murphy CT, Kenyon C. 2003. Regulation of Aging and Age-Related Disease by DAF-16 and Heat-Shock Factor. Science 300: 1142-1145.
","pubmedId":"","doi":"10.1126/science.1083701"},{"reference":"Jhaveri N, Bhullar H, Sternberg PW, Gupta BP. 2025. Heat tolerance and genetic adaptations in Caenorhabditis briggsae: insights from comparative studies with Caenorhabditis elegans. GENETICS 230: 10.1093/genetics/iyaf061.
","pubmedId":"","doi":"10.1093/genetics/iyaf061"},{"reference":"Kourtis N, Nikoletopoulou V, Tavernarakis N. 2012. Small heat-shock proteins protect from heat-stroke-associated neurodegeneration. Nature 490: 213-218.
","pubmedId":"","doi":"10.1038/nature11417"},{"reference":"Kovács Dn, Biró JnBs, Ahmed S, Kovács Mr, Sigmond Tm, Hotzi B, et al., Barna. 2024. Age‐dependent heat shock hormesis to
McColl G, Rogers AN, Alavez S, Hubbard AE, Melov S, Link CD, et al., Lithgow. 2010. Insulin-like Signaling Determines Survival during Stress via Posttranscriptional Mechanisms in C. elegans. Cell Metabolism 12: 260-272.
","pubmedId":"","doi":"10.1016/j.cmet.2010.08.004"},{"reference":"Morley JF, Morimoto RI. 2004. Regulation of Longevity inCaenorhabditis elegansby Heat Shock Factor and Molecular Chaperones. Molecular Biology of the Cell 15: 657-664.
","pubmedId":"","doi":"10.1091/mbc.e03-07-0532"},{"reference":"Morton EA, Lamitina T. 2012. Caenorhabditis elegans
Prahlad V, Cornelius T, Morimoto RI. 2008. Regulation of the Cellular Heat Shock Response in\n Caenorhabditis elegans\n by Thermosensory Neurons. Science 320: 811-814.
","pubmedId":"","doi":"10.1126/science.1156093"},{"reference":"Prasad A, Croydon-Sugarman MJF, Murray RL, Cutter AD. 2010. TEMPERATURE-DEPENDENT FECUNDITY ASSOCIATES WITH LATITUDE IN CAENORHABDITIS BRIGGSAE. Evolution 65: 52-63.
","pubmedId":"","doi":"10.1111/j.1558-5646.2010.01110.x"},{"reference":"Schmeisser S, Priebe S, Groth M, Monajembashi S, Hemmerich P, Guthke R, Platzer M, Ristow M. 2013. Neuronal ROS signaling rather than AMPK/sirtuin-mediated energy sensing links dietary restriction to lifespan extension. Molecular Metabolism 2: 92-102.
","pubmedId":"","doi":"10.1016/j.molmet.2013.02.002"},{"reference":"Seetharaman A, Cumbo P, Bojanala N, Gupta BP. 2010. Conserved mechanism of Wnt signaling function in the specification of vulval precursor fates in C. elegans and C. briggsae. Developmental Biology 346: 128-139.
","pubmedId":"","doi":"10.1016/j.ydbio.2010.07.003"},{"reference":"Steinkraus KA, Smith ED, Davis C, Carr D, Pendergrass WR, Sutphin GL, Kennedy BK, Kaeberlein M. 2008. Dietary restriction suppresses proteotoxicity and enhances longevity by an\n hsf‐1\n ‐dependent mechanism in\n Caenorhabditis elegans. Aging Cell 7: 394-404.
","pubmedId":"","doi":"10.1111/j.1474-9726.2008.00385.x"},{"reference":"van den Berg W, Gupta BP. 2025. Genome-Wide Temporal Gene Expression Reveals a Post-Reproductive Shift in the Nematode Caenorhabditis briggsae. Genome Biology and Evolution 17: 10.1093/gbe/evaf057.
","pubmedId":"","doi":"10.1093/gbe/evaf057"},{"reference":"Volovik Y, Maman M, Dubnikov T, Bejerano‐Sagie M, Joyce D, Kapernick EA, Cohen E, Dillin A. 2012. Temporal requirements of heat shock factor‐1 for longevity assurance. Aging Cell 11: 491-499.
","pubmedId":"","doi":"10.1111/j.1474-9726.2012.00811.x"}],"title":"The heat shock factor Cbr-HSF-1 is necessary for lifespan maintenance in C. briggsae
","reviews":[{"reviewer":{"displayName":"Todd Lamitina"},"openAcknowledgement":false,"status":{"submitted":true}}],"curatorReviews":[{"curator":{"displayName":"Gary Craig Schindelman"},"openAcknowledgement":false,"submitted":null}]},{"id":"d80daa15-e92c-4567-b7a3-cc97c57a8a2c","decision":"accept","abstract":"The heat shock response is a conserved mechanism that plays a critical role in organismal survival under thermal stress. Caenorhabditis briggsae is a widely used model organism for comparative studies involving its well-known cousin C. elegans and exhibits increased thermotolerance under heat stress. In C. elegans, the transcription factor HSF-1 has been well characterized for its role in many processes including development, thermotolerance, and lifespan. We recently showed that Cbr-hsf-1 is necessary for fertility and protection against heat stress. Here, we report that Cbr-hsf-1 also plays essential roles during development and adulthood to maintain the lifespan of animals.
","acknowledgements":"","authors":[{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","formalAnalysis","investigation","methodology","writing_originalDraft","writing_reviewEditing"],"email":"bhullh2@mcmaster.ca","firstName":"Harvir","lastName":"Bhullar","submittingAuthor":true,"correspondingAuthor":true,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","formalAnalysis"],"email":"diasj8@mcmaster.ca","firstName":"Jordan","lastName":"Dias","submittingAuthor":false,"correspondingAuthor":false,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","formalAnalysis"],"email":"pastagik@mcmaster.ca","firstName":"Khushi","lastName":"Pastagia","submittingAuthor":false,"correspondingAuthor":false,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","methodology","formalAnalysis","investigation"],"email":"vandew1@mcmaster.ca","firstName":"Wouter","lastName":"van den Berg","submittingAuthor":false,"correspondingAuthor":false,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["conceptualization","fundingAcquisition","methodology","project","resources","supervision","writing_reviewEditing"],"email":"guptab@mcmaster.ca","firstName":"Bhagwati P","lastName":"Gupta","submittingAuthor":false,"correspondingAuthor":true,"equalContribution":false,"WBId":null,"orcid":"0000-0001-8572-7054"}],"awards":[],"conflictsOfInterest":"The authors declare that there are no conflicts of interest present.
","dataTable":{"url":null},"extendedData":[],"funding":"Supported by Natural Sciences and Engineering Research Council (Canada) to Bhagwati P Gupta.
","image":{"url":"https://portal.micropublication.org/uploads/af720d2a3ecbec3dfb62de520d816cf9.png"},"imageCaption":"(A) Schematic of RNAi treatment timelines used for lifespan assays. (B-D) Lifespan plots of animals. Control refers to worms fed with bacteria carrying an empty vector (L4440). RNAi was administered from (B) embryogenesis to Day 1 adulthood at 20°C, (C) from embryogenesis to Day 1 adulthood at 30°C, and (D) from Day 1 adulthood onward at 20°C. Survival curves compare Cbr-hsf-1(RNAi) to control and were analyzed using Kaplan-Meier log-rank (Mantel-Cox) test. (E) Summary table of lifespan metrics corresponding to the data presented in panels B-D. SEM, standard error of the mean; C.I., confidence interval; N, number of animals examined. (F) Transcript levels of CBG19186 in Day 1 control (L4440) and Cbr-hsf-1(RNAi) worms . Data was analyzed using Student's t-test. Data is presented as mean ± SEM. (G,H) Normalized transcript counts of hsf-1 across specific adult stages in (G) C. briggsae and (H) C. elegans, based on previously published datasets (see Methods). Independent biological replicates for each time point are shown. The trend line indicates mean values. The Y-axis is displayed on a log scale. (I) Survival of Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms following heat stress exposure. Statistical significance was assessed using the Mann-Whitney test. Bars represent mean ± SD (standard deviation). Total n = 140-154 per RNAi condition. (J) Survival of Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms following 24-hour ER stress exposure. Statistical significance was assessed using Wilcoxon matched-pairs signed-rank test. Bars represent mean ± SD. Total n = 304-347 per RNAi condition. Dots on bar graphs represent individual biological batches. For lifespan assays (B-D), 6-8 biological batches were performed per condition. For stress survival assays (I, J), 3-6 biological batches were performed per condition. Asterisks indicate statistically significant differences (**p < 0.01, **** p < 0.0001).
","imageTitle":"Survival and stress response of C. briggsae following hsf-1 RNAi knockdown
","methods":"Worm maintenance and RNAi
Worms were cultured on nematode growth medium (NGM) agar plates seeded with Escherichia coli OP50 using standard methods. An RNAi-sensitive C. briggsae strain (JU1018 mfIs42[Cel-sid-2(+); Cel-myo-2::DsRed]) expressing the C. elegans sid-2 transgene was used for all experiments (Seetharaman, et al. 2010). RNAi was performed by feeding worms E. coli HT115 bacteria that carried double-stranded RNA targeting Cbr-hsf-1 (Jhaveri, et al. 2025). HT115 bacteria harboring the empty vector (L4440) served as RNAi controls.
Lifespan
Embryos were obtained by allowing gravid JU1018 adults to lay eggs for 2-3 hours on the appropriate plates. For developmental knockdown, worms were exposed to RNAi from the embryonic stage and maintained at either 20°C or 30°C until Day 1 of adulthood, after which they were transferred to OP50 seeded NGM plates and maintained at 20°C. For adult-specific knockdown, worms were grown on OP50 plates until Day 1 of adulthood and then transferred to RNAi plates, remaining at 20°C for the duration of the experiment. Animals were scored for survival every 1-2 days by gentle prodding with a platinum wire. Individuals that failed to respond were scored as dead. Worms were transferred to fresh plates as needed.
RT-qPCR
Approximately 6-8 JU1018 gravid hermaphrodites were placed on RNAi plates seeded with the appropriate bacteria and allowed to lay eggs for 2-3 hours. The adults were then removed, and the progeny were allowed to develop to the Day 1 adult stage. Worms were collected by washing them off plates with M9 buffer and immediately frozen in RNAzol RT (Molecular Research Center, catalog number: RNN190) for RNA extraction. Following RNA extraction, cDNA was synthesized using the LunaScript RT SuperMix Kit (New England Biolabs, catalog number: M3010L), and gene expression was quantified by RT-qPCR using the Bio-Rad cycler CFX 96 and the SensiFAST SYBR No-ROX Kit (FroggaBio, catalog number: BIO-98005). Three independent biological replicates were performed, and results from all replicates were combined for statistical analysis.
Cbr-iscu-1 was used as the housekeeping gene for normalization. Primer sequences for each gene are listed below.
GL1406 (Cbr-iscu-1) FP: GCTTCAAATCAGTCTCGCTGC; GL1407 (Cbr-iscu-1) RP: GTGCCGACGTTCTTGTCGTTT;
GL1701 (CBG19186) FP: TGGAATTGATCTTCCTTGGACTGC; GL1702 (CBG19186) RP: CGCGCTTTCTCCTTTGTTGTTG
Stress assays
Synchronized populations were generated by allowing gravid JU1018 adults to lay eggs for 2 hours on OP50 seeded NGM plates. Adults were removed after egg laying, and progeny were maintained at 20°C until Day 1 of adulthood.
For heat shock, we followed the previously published protocol from our group (Jhaveri, et al. 2025). Briefly, Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms were transferred to OP50 seeded NGM plates equilibrated at room temperature (20°C). Plates were then transferred to a 35°C incubator for 8 or 10 hours. After heat treatment, plates were returned to a 20°C incubator, and worms were allowed to recover for 24 hours before survival was scored.
For ER stress, Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms were exposed to 50 ng/µL tunicamycin (Sigma-Aldrich, catalog number: T7765) in 24-well plates for 24 hours. Following exposure, worms were scored for survival. Animals unresponsive to touch and exhibiting a rigid, rod-like morphology were scored as dead.
hsf-1 expression
Gene expression data for C. briggsae and C. elegans were obtained from published datasets and processed using RNA STAR for alignment and featureCounts for quantification (Schmeisser, et al. 2013; van den Berg and Gupta 2025). Counts from biological replicates for each time point (C. briggsae: days 1, 3, 6, 9; C. elegans: days 1, 5, 10 of adulthood) were plotted.
Statistical analysis
Lifespan data were analyzed using OASIS 2 (Han, et al. 2016). RT-qPCR data was analyzed using Bio-Rad CFX Maestro 3.1 software. All other analyses were performed using GraphPad Prism version 10.6.1. All figures were generated using GraphPad Prism. Statistical tests for each experiment are indicated in the figure legend.
","reagents":"","patternDescription":"The nematode C. briggsae is commonly used in comparative biological studies alongside its close relative C. elegans. We and others have shown that C. briggsae exhibits increased thermotolerance relative to C. elegans, suggesting that these two species may differ in the mechanisms that regulate stress resistance at elevated temperatures (Felix and Duveau 2012; Jhaveri, et al. 2025; Prasad, et al. 2011).
In C. elegans, the heat shock response is regulated by the transcription factor HSF-1, whose function has been extensively characterized (Morton and Lamitina 2013). Two well described hsf-1 mutant alleles (ok600 and sy441) highlight the essential role of the gene in development and stress regulation. Strong loss of hsf-1 function (ok600) causes severe developmental defects that include arrest at the L2-L3 larval stages (Morton and Lamitina 2013). The partial loss-of-function allele (sy441) and RNAi-mediated knockdown have revealed additional roles in lifespan regulation and stress physiology (Garigan, et al. 2002; Hajdu-Cronin, et al. 2004; Hsu, et al. 2003; Morley and Morimoto 2004; Morton and Lamitina 2013; Volovik, et al. 2012).
Studies on HSF-1's role in C. elegans thermotolerance have reported variable results, which may be in part due to context dependent contribution of the gene to stress resistance. Depending on the age of the animals, the extent of HSF-1 depletion, and assay conditions used, reduced HSF-1 activity has been reported to lower thermotolerance (Finger, et al. 2021; Prahlad, et al. 2008; Steinkraus, et al. 2008), enhance thermotolerance (Golden, et al. 2020), have no effect (Kourtis, et al. 2012; McColl, et al. 2010), reduce thermotolerance after heat pre-treatment (Kourtis, et al. 2012; McColl, et al. 2010), or even enhance survival in young adults immediately after heat shock, with thermotolerance declining with age (Kovacs, et al. 2024). Recent studies have also linked HSF-1 to endoplasmic reticulum (ER) stress responses and survival on tunicamycin, indicating its function extends beyond the canonical heat shock response (Ahmed, et al. 2026; Alcala, et al. 2026; Kovacs, et al. 2024). Together, these findings raise the question of whether the C. briggsae hsf-1 ortholog, Cbr-hsf-1 plays similar roles in C. briggsae.
We recently found that RNAi knockdown of Cbr-hsf-1 from embryogenesis to Day 1 adult stage caused no obvious phenotype at 20°C but resulted in sterility at 30°C (Jhaveri, et al. 2025). To further investigate the role of Cbr-hsf-1, we performed lifespan assays following RNAi-mediated knockdown initiated either during development or adulthood (Figure 1A). The developmental knockdown at 20°C caused a significant reduction in lifespan of animals (Figure 1A, B, E). To determine whether elevated temperature would further compromise survival, the experiment was repeated at 30°C. While the reduction in mean lifespan was similar (27% lower at 20°C and 24% lower at 30°C, compared to controls), population decline was faster at 30°C, as shown by a greater reduction in time to reach 90% mortality (33% at 30°C vs. 17% at 20°C, relative to controls) (Figure 1E).
To assess the post-developmental requirements of Cbr-hsf-1, RNAi was initiated at 20°C on Day 1 of adulthood. Adult-specific knockdown also significantly shortened the lifespan of animals (Figure 1D, E), indicating that Cbr-hsf-1 is required during adulthood for normal lifespan maintenance. Consistent with this, hsf-1 is expressed in both C. briggsae and C. elegans adults (Figure 1G, H). Overall, these results suggest that Cbr-hsf-1 is required during both development and adulthood for normal lifespan of C. briggsae animals.
To verify the effectiveness of Cbr-hsf-1 RNAi knockdown at 20°C, we measured transcript levels of CBG19186, the closest C. briggsae ortholog of a small heat shock protein hsp-16.2 that is a known target of HSF-1 in C. elegans (Jhaveri, et al. 2025; Hajdu-Cronin, et al. 2004; Jones, et al. 1986). Expression of CBG19186 was significantly reduced in Cbr-hsf-1(RNAi) animals relative to controls (Figure 1F), consistent with reduced HSF-1 activity. RNAi efficacy at 30°C was supported by the sterility phenotype previously reported for Cbr-hsf-1(RNAi) animals (Jhaveri, et al. 2025).
We next assessed Cbr-hsf-1's contribution to acute stress resistance. Following heat shock at 35°C for 8 or 10 hours, or after 24 hours of exposure to tunicamycin, Cbr-hsf-1(RNAi) animals exhibited survival comparable to controls (Figure 1I, J), suggesting that Cbr-hsf-1 is not required for survival under these assay conditions.
Together, these data show that Cbr-hsf-1 plays an important role in lifespan maintenance in C. briggsae, while having little or no detectable contribution to survival in the acute stress assays tested here. Similar differences between lifespan regulation and acute stress resistance have been reported in C. elegans, where reduced HSF-1 activity consistently shortens lifespan but has variable effects on thermotolerance depending on experimental conditions, developmental stage, and degree of knockdown (Morley and Morimoto 2004; Volovik, et al. 2012; Hsu, et al. 2003; Finger et al. 2021; Golden et al. 2020; Kourtis et al. 2012; McColl et al. 2010; Kovacs et al. 2024).
Our results in C. briggsae suggest that HSF-1's role in lifespan maintenance in both species may be at least partially separable from its role in acute stress survival. Because RNAi may not fully deplete Cbr-hsf-1 activity, it remains possible that stronger loss-of-function approaches could reveal a role in acute stress survival. Further studies using genetic null or strong hypomorphic alleles of Cbr-hsf-1 will be needed to more comprehensively study its role in C. briggsae.
","references":[{"reference":"Ahmed S, Kovács Dn, Kovács Mr, Kosztelnik Mn, Hotzi B, Sigmond Tm, et al., Barna. 2026. Heat shock factor-1 alleviates ER-stress in Caenorhabditis elegans. Scientific Reports 16: 10.1038/s41598-026-43060-3.
","pubmedId":"","doi":"10.1038/s41598-026-43060-3"},{"reference":"Alcala A, Castro Torres T, Aviles Barahona R, Frankino PA, Higuchi-Sanabria R, Garcia G. 2026. A non-canonical role for UPR\n ER\n during heat stress in\n C. elegans. : 10.64898/2026.01.08.698479.
","pubmedId":"","doi":" 10.64898/2026.01.08.698479"},{"reference":"Félix MA, Duveau F. 2012. Population dynamics and habitat sharing of natural populations of Caenorhabditis elegans and C. briggsae. BMC Biology 10: 10.1186/1741-7007-10-59.
","pubmedId":"","doi":"10.1186/1741-7007-10-59"},{"reference":"Finger F, Ottens F, Hoppe T. 2021. The Argonaute Proteins ALG-1 and ALG-2 Are Linked to Stress Resistance and Proteostasis. MicroPubl Biol 2021: 10.17912/micropub.biology.000457.
","pubmedId":"34723149","doi":"10.17912/micropub.biology.000457"},{"reference":"Garigan D, Hsu AL, Fraser AG, Kamath RS, Ahringer J, Kenyon C. 2002. Genetic Analysis of Tissue Aging in Caenorhabditis elegans: A Role for Heat-Shock Factor and Bacterial Proliferation. Genetics 161: 1101-1112.
","pubmedId":"","doi":"10.1093/genetics/161.3.1101"},{"reference":"Golden NL, Plagens RN, Kim Guisbert KS, Guisbert E. 2020. Standardized Methods for Measuring Induction of the Heat Shock Response in <em>Caenorhabditis elegans</em>. Journal of Visualized Experiments : 10.3791/61030.
","pubmedId":"","doi":"10.3791/61030"},{"reference":"Hajdu-Cronin YM, Chen WJ, Sternberg PW. 2004. The L-type cyclin CYL-1 and the heat-shock-factor HSF-1 are required for heat-shock-induced protein expression in Caenorhabditis elegans. Genetics 168(4): 1937-49.
","pubmedId":"15611166","doi":""},{"reference":"Han SK, Lee D, Lee H, Kim D, Son HG, Yang JS, Lee SJV, Kim S. 2016. OASIS 2: online application for survival analysis 2 with features for the analysis of maximal lifespan and healthspan in aging research. Oncotarget 7: 56147-56152.
","pubmedId":"","doi":"10.18632/oncotarget.11269"},{"reference":"Hsu AL, Murphy CT, Kenyon C. 2003. Regulation of Aging and Age-Related Disease by DAF-16 and Heat-Shock Factor. Science 300: 1142-1145.
","pubmedId":"","doi":"10.1126/science.1083701"},{"reference":"Jhaveri N, Bhullar H, Sternberg PW, Gupta BP. 2025. Heat tolerance and genetic adaptations in Caenorhabditis briggsae: insights from comparative studies with Caenorhabditis elegans. GENETICS 230: 10.1093/genetics/iyaf061.
","pubmedId":"","doi":"10.1093/genetics/iyaf061"},{"reference":"Jones D, Russnak RH, Kay RJ, Candido EP. 1986. Structure, expression, and evolution of a heat shock gene locus in Caenorhabditis elegans that is flanked by repetitive elements. J Biol Chem 261(26): 12006-15.
","pubmedId":"3017958","doi":""},{"reference":"Kourtis N, Nikoletopoulou V, Tavernarakis N. 2012. Small heat-shock proteins protect from heat-stroke-associated neurodegeneration. Nature 490: 213-218.
","pubmedId":"","doi":"10.1038/nature11417"},{"reference":"Kovács Dn, Biró JnBs, Ahmed S, Kovács Mr, Sigmond Tm, Hotzi B, et al., Barna. 2024. Age‐dependent heat shock hormesis to
McColl G, Rogers AN, Alavez S, Hubbard AE, Melov S, Link CD, et al., Lithgow. 2010. Insulin-like Signaling Determines Survival during Stress via Posttranscriptional Mechanisms in C. elegans. Cell Metabolism 12: 260-272.
","pubmedId":"","doi":"10.1016/j.cmet.2010.08.004"},{"reference":"Morley JF, Morimoto RI. 2004. Regulation of Longevity inCaenorhabditis elegansby Heat Shock Factor and Molecular Chaperones. Molecular Biology of the Cell 15: 657-664.
","pubmedId":"","doi":"10.1091/mbc.e03-07-0532"},{"reference":"Morton EA, Lamitina T. 2012. Caenorhabditis elegans
Prahlad V, Cornelius T, Morimoto RI. 2008. Regulation of the Cellular Heat Shock Response in\n Caenorhabditis elegans\n by Thermosensory Neurons. Science 320: 811-814.
","pubmedId":"","doi":"10.1126/science.1156093"},{"reference":"Prasad A, Croydon-Sugarman MJF, Murray RL, Cutter AD. 2010. TEMPERATURE-DEPENDENT FECUNDITY ASSOCIATES WITH LATITUDE IN CAENORHABDITIS BRIGGSAE. Evolution 65: 52-63.
","pubmedId":"","doi":"10.1111/j.1558-5646.2010.01110.x"},{"reference":"Schmeisser S, Priebe S, Groth M, Monajembashi S, Hemmerich P, Guthke R, Platzer M, Ristow M. 2013. Neuronal ROS signaling rather than AMPK/sirtuin-mediated energy sensing links dietary restriction to lifespan extension. Molecular Metabolism 2: 92-102.
","pubmedId":"","doi":"10.1016/j.molmet.2013.02.002"},{"reference":"Seetharaman A, Cumbo P, Bojanala N, Gupta BP. 2010. Conserved mechanism of Wnt signaling function in the specification of vulval precursor fates in C. elegans and C. briggsae. Developmental Biology 346: 128-139.
","pubmedId":"","doi":"10.1016/j.ydbio.2010.07.003"},{"reference":"Steinkraus KA, Smith ED, Davis C, Carr D, Pendergrass WR, Sutphin GL, Kennedy BK, Kaeberlein M. 2008. Dietary restriction suppresses proteotoxicity and enhances longevity by an\n hsf‐1\n ‐dependent mechanism in\n Caenorhabditis elegans. Aging Cell 7: 394-404.
","pubmedId":"","doi":"10.1111/j.1474-9726.2008.00385.x"},{"reference":"van den Berg W, Gupta BP. 2025. Genome-Wide Temporal Gene Expression Reveals a Post-Reproductive Shift in the Nematode Caenorhabditis briggsae. Genome Biology and Evolution 17: 10.1093/gbe/evaf057.
","pubmedId":"","doi":"10.1093/gbe/evaf057"},{"reference":"Volovik Y, Maman M, Dubnikov T, Bejerano‐Sagie M, Joyce D, Kapernick EA, Cohen E, Dillin A. 2012. Temporal requirements of heat shock factor‐1 for longevity assurance. Aging Cell 11: 491-499.
","pubmedId":"","doi":"10.1111/j.1474-9726.2012.00811.x"}],"title":"The heat shock factor Cbr-HSF-1 is necessary for lifespan maintenance in C. briggsae
","reviews":[],"curatorReviews":[{"curator":{"displayName":"Gary Craig Schindelman"},"openAcknowledgement":false,"submitted":"1782438984630"}]},{"id":"d45c5abe-e11c-43ea-8f2f-49d6ae30f6d0","decision":"publish","abstract":"The heat shock response is a conserved mechanism that plays a critical role in organismal survival under thermal stress. Caenorhabditis briggsae is a widely used model organism for comparative studies involving its well-known cousin C. elegans and exhibits increased thermotolerance under heat stress. In C. elegans, the transcription factor HSF-1 has been well characterized for its role in many processes including development, thermotolerance, and lifespan. We recently showed that Cbr-hsf-1 is necessary for fertility and protection against heat stress. Here, we report that Cbr-hsf-1 also plays essential roles during development and adulthood to maintain the lifespan of animals.
","acknowledgements":"","authors":[{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","formalAnalysis","investigation","methodology","writing_originalDraft","writing_reviewEditing"],"email":"bhullh2@mcmaster.ca","firstName":"Harvir","lastName":"Bhullar","submittingAuthor":true,"correspondingAuthor":true,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","formalAnalysis"],"email":"diasj8@mcmaster.ca","firstName":"Jordan","lastName":"Dias","submittingAuthor":false,"correspondingAuthor":false,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","formalAnalysis"],"email":"pastagik@mcmaster.ca","firstName":"Khushi","lastName":"Pastagia","submittingAuthor":false,"correspondingAuthor":false,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["dataCuration","methodology","formalAnalysis","investigation"],"email":"vandew1@mcmaster.ca","firstName":"Wouter","lastName":"van den Berg","submittingAuthor":false,"correspondingAuthor":false,"equalContribution":false,"WBId":null,"orcid":null},{"affiliations":["McMaster University, Hamilton, ON, CA"],"departments":["Biology"],"credit":["conceptualization","fundingAcquisition","methodology","project","resources","supervision","writing_reviewEditing"],"email":"guptab@mcmaster.ca","firstName":"Bhagwati P","lastName":"Gupta","submittingAuthor":false,"correspondingAuthor":true,"equalContribution":false,"WBId":null,"orcid":"0000-0001-8572-7054"}],"awards":[],"conflictsOfInterest":"The authors declare that there are no conflicts of interest present.
","dataTable":{"url":null},"extendedData":[],"funding":"Supported by Natural Sciences and Engineering Research Council (Canada) to Bhagwati P Gupta.
","image":{"url":"https://portal.micropublication.org/uploads/af720d2a3ecbec3dfb62de520d816cf9.png"},"imageCaption":"(A) Schematic of RNAi treatment timelines used for lifespan assays. (B-D) Lifespan curves of animals. Control animals were fed bacteria carrying an empty vector (L4440). RNAi was administered from (B) embryogenesis to Day 1 adulthood at 20°C, (C) from embryogenesis to Day 1 adulthood at 30°C, and (D) from Day 1 adulthood onward at 20°C. Survival curves compare Cbr-hsf-1(RNAi) to control and were analyzed using the Kaplan-Meier log-rank (Mantel-Cox) test. (E) Summary table of lifespan metrics corresponding to the data presented in panels B-D. SEM, standard error of the mean; C.I., confidence interval; n, number of animals examined. (F) Transcript levels of CBG19186 in Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms . Data was analyzed using Student's t-test. Data is presented as mean ± SEM. (G,H) Normalized transcript counts of hsf-1 across specific adult stages in (G) C. briggsae and (H) C. elegans, based on previously published datasets (see Methods). Independent biological replicates for each time point are shown. The trend line indicates mean values. The Y-axis is displayed on a log scale. (I) Survival of Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms following heat stress exposure. Statistical significance was assessed using the Mann-Whitney test. Bars represent mean ± SD (standard deviation). Total n = 140-154 animals per RNAi condition. (J) Survival of Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms following 24-hour ER stress exposure. Statistical significance was assessed using the Wilcoxon matched-pairs signed-rank test. Bars represent mean ± SD. Total n = 304-347 animals per RNAi condition. Dots on bar graphs represent individual biological batches. For lifespan assays (B-D), 6-8 biological batches were performed per condition. For stress survival assays (I, J), 3-6 biological batches were performed per condition. Asterisks indicate statistically significant differences (**p < 0.01, **** p < 0.0001).
","imageTitle":"Survival and stress response of C. briggsae following hsf-1 RNAi knockdown
","methods":"Worm maintenance and RNAi
Worms were cultured on nematode growth medium (NGM) agar plates seeded with Escherichia coli OP50 using standard methods. An RNAi-sensitive C. briggsae strain (JU1018 mfIs42[Cel-sid-2(+); Cel-myo-2::DsRed]) expressing the C. elegans sid-2 transgene was used for all experiments (Seetharaman, et al. 2010). RNAi was performed by feeding worms E. coli HT115 bacteria that carried double-stranded RNA targeting Cbr-hsf-1 (Jhaveri, et al. 2025). HT115 bacteria harboring the empty vector (L4440) served as RNAi controls.
Lifespan
Embryos were obtained by allowing gravid JU1018 adults to lay eggs for 2-3 hours on the appropriate plates. For developmental knockdown, worms were exposed to RNAi from the embryonic stage and maintained at either 20°C or 30°C until Day 1 of adulthood, after which they were transferred to OP50 seeded NGM plates and maintained at 20°C. For adult-specific knockdown, worms were grown on OP50 plates until Day 1 of adulthood and then transferred to RNAi plates, remaining at 20°C for the duration of the experiment. Animals were scored for survival every 1-2 days by gentle prodding with a platinum wire. Animals that failed to respond were scored as dead. Worms were transferred to fresh plates as needed.
RT-qPCR
Approximately 6-8 JU1018 gravid hermaphrodites were placed on RNAi plates seeded with the appropriate bacteria and allowed to lay eggs for 2-3 hours. The adults were then removed, and the progeny were allowed to develop to the Day 1 adult stage. Worms were collected by washing them off plates with M9 buffer and immediately frozen in RNAzol RT (Molecular Research Center, catalog number: RNN190) for RNA extraction. Following RNA extraction, cDNA was synthesized using the LunaScript RT SuperMix Kit (New England Biolabs, catalog number: M3010L), and gene expression was quantified by RT-qPCR using the Bio-Rad cycler CFX 96 and the SensiFAST SYBR No-ROX Kit (FroggaBio, catalog number: BIO-98005). Three independent biological replicates were performed, and results from all replicates were combined for statistical analysis.
Cbr-iscu-1 was used as the housekeeping gene for normalization. Primer sequences for each gene are listed below.
GL1406 (Cbr-iscu-1) FP: GCTTCAAATCAGTCTCGCTGC
GL1407 (Cbr-iscu-1) RP: GTGCCGACGTTCTTGTCGTTT
GL1701 (CBG19186) FP: CCGTCCAAGACCATTCTCTGT
GL1702 (CBG19186) RP: ACTGGGAGACGTTGAGGTTG
Stress assays
Synchronized populations were generated by allowing gravid JU1018 adults to lay eggs for 2 hours on OP50 seeded NGM plates. Adults were removed after egg laying, and progeny were maintained at 20°C until Day 1 of adulthood.
For heat shock, we followed the previously published protocol from our group (Jhaveri, et al. 2025). Briefly, Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms were transferred to OP50 seeded NGM plates equilibrated at room temperature (20°C). Plates were then transferred to a 35°C incubator for 8 or 10 hours. After heat treatment, plates were returned to a 20°C incubator, and worms were allowed to recover for 24 hours before survival was scored.
For ER stress, Day 1 adult control (L4440) and Cbr-hsf-1(RNAi) worms were exposed to 50 ng/µL tunicamycin (Sigma-Aldrich, catalog number: T7765) in 24-well plates for 24 hours. Following exposure, worms were scored for survival. Animals unresponsive to touch and exhibiting a rigid, rod-like morphology were scored as dead.
hsf-1 expression
Gene expression data for C. briggsae and C. elegans were obtained from published datasets and processed using RNA STAR for alignment and featureCounts for quantification (Schmeisser, et al. 2013; van den Berg and Gupta 2025). Gene counts were normalized in R using DESeq2, and normalized hsf-1 expression values were extracted for adult time points (C. briggsae: days 1, 3, 6, 9; C. elegans: days 1, 5, 10 of adulthood).
Statistical analysis
Lifespan data were analyzed using OASIS 2 (Han, et al. 2016). RT-qPCR data was analyzed using Bio-Rad CFX Maestro 3.1 software. All other analyses were performed using GraphPad Prism version 10.6.1. All figures were generated using GraphPad Prism. Statistical tests for each experiment are indicated in the figure legend.
","reagents":"","patternDescription":"The nematode C. briggsae is commonly used in comparative biological studies alongside its close relative C. elegans. We and others have shown that C. briggsae exhibits increased thermotolerance relative to C. elegans, suggesting that these two species may differ in the mechanisms that regulate stress resistance at elevated temperatures (Felix and Duveau 2012; Jhaveri, et al. 2025; Prasad, et al. 2011).
In C. elegans, the heat shock response is regulated by the transcription factor HSF-1, whose function has been extensively characterized (Morton and Lamitina 2013). Two well described hsf-1 mutant alleles (ok600 and sy441) highlight the essential role of the gene in development and stress regulation. Strong loss of hsf-1 function (ok600) causes severe developmental defects that include arrest at the L2-L3 larval stages (Morton and Lamitina 2013). The partial loss-of-function allele (sy441) and RNAi-mediated knockdown have revealed additional roles in lifespan regulation and stress physiology (Garigan, et al. 2002; Hajdu-Cronin, et al. 2004; Hsu, et al. 2003; Morley and Morimoto 2004; Morton and Lamitina 2013; Volovik, et al. 2012).
Studies on HSF-1's role in C. elegans thermotolerance have reported variable results, which may be in part due to context dependent contribution of the gene to stress resistance. Depending on the age of the animals, the extent of HSF-1 depletion, and assay conditions used, reduced HSF-1 activity has been reported to lower thermotolerance (Finger, et al. 2021; Prahlad, et al. 2008; Steinkraus, et al. 2008), enhance thermotolerance (Golden, et al. 2020), have no effect (Kourtis, et al. 2012; McColl, et al. 2010), reduce thermotolerance after heat pre-treatment (Kourtis, et al. 2012; McColl, et al. 2010), or even enhance survival in young adults immediately after heat shock, with thermotolerance declining with age (Kovacs, et al. 2024). Recent studies have also linked HSF-1 to endoplasmic reticulum (ER) stress responses and survival on tunicamycin, indicating its function extends beyond the canonical heat shock response (Ahmed, et al. 2026; Alcala, et al. 2026; Kovacs, et al. 2024). Together, these findings raise the question of whether the C. briggsae hsf-1 ortholog, Cbr-hsf-1 plays similar roles in C. briggsae.
We recently found that RNAi knockdown of Cbr-hsf-1 from embryogenesis to Day 1 adult stage caused no obvious phenotype at 20°C but resulted in sterility at 30°C (Jhaveri, et al. 2025). To further investigate the role of Cbr-hsf-1, we performed lifespan assays following RNAi-mediated knockdown initiated either during development or adulthood (Figure 1A). The developmental knockdown at 20°C caused a significant reduction in lifespan of animals (Figure 1A, B, E). To determine whether elevated temperature would further compromise survival, the experiment was repeated at 30°C. While the reduction in mean lifespan was similar (27% lower at 20°C and 24% lower at 30°C, compared to controls), population decline was faster at 30°C, as shown by a greater reduction in time to reach 90% mortality (33% at 30°C vs. 17% at 20°C, relative to controls) (Figure 1E).
To assess the post-developmental requirements of Cbr-hsf-1, RNAi was initiated at 20°C on Day 1 of adulthood. Adult-specific knockdown also significantly shortened the lifespan of animals (Figure 1D, E), indicating that Cbr-hsf-1 is required during adulthood for normal lifespan maintenance. Consistent with this, hsf-1 is expressed in both C. briggsae and C. elegans adults (Figure 1G, H). Overall, these results suggest that Cbr-hsf-1 is required during both development and adulthood for normal lifespan of C. briggsae animals.
To verify the effectiveness of Cbr-hsf-1 RNAi knockdown at 20°C, we measured transcript levels of CBG19186, the closest C. briggsae ortholog of a small heat shock protein hsp-16.2 that is a known target of HSF-1 in C. elegans (Jhaveri, et al. 2025; Hajdu-Cronin, et al. 2004; Jones, et al. 1986). Expression of CBG19186 was significantly reduced in Cbr-hsf-1(RNAi) animals relative to controls (Figure 1F), consistent with reduced HSF-1 activity. RNAi efficacy at 30°C was supported by the sterility phenotype previously reported for Cbr-hsf-1(RNAi) animals (Jhaveri, et al. 2025).
We next assessed Cbr-hsf-1's contribution to acute stress resistance. Following heat shock at 35°C for 8 or 10 hours, or after 24 hours of exposure to tunicamycin, Cbr-hsf-1(RNAi) animals exhibited survival comparable to controls (Figure 1I, J), suggesting that Cbr-hsf-1 is not required for survival under these assay conditions.
Together, these data show that Cbr-hsf-1 plays an important role in lifespan maintenance in C. briggsae, while having little or no detectable contribution to survival in the acute stress assays tested here. Similar differences between lifespan regulation and acute stress resistance have been reported in C. elegans, where reduced HSF-1 activity consistently shortens lifespan but has variable effects on thermotolerance depending on experimental conditions, developmental stage, and degree of knockdown (Morley and Morimoto 2004; Volovik, et al. 2012; Hsu, et al. 2003; Finger et al. 2021; Golden et al. 2020; Kourtis et al. 2012; McColl et al. 2010; Kovacs et al. 2024).
Our results in C. briggsae suggest that HSF-1's role in lifespan maintenance in both species may be at least partially separable from its role in acute stress survival. Because RNAi may not fully deplete Cbr-hsf-1 activity, it remains possible that stronger loss-of-function approaches could reveal a role in acute stress survival. Further studies using genetic null or strong hypomorphic alleles of Cbr-hsf-1 will be needed to more comprehensively study its role in C. briggsae.
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","pubmedId":"","doi":"10.1111/j.1474-9726.2012.00811.x"}],"title":"The heat shock factor Cbr-HSF-1 is necessary for lifespan maintenance in C. briggsae
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