Repression of the Heat Shock Response Is a Programmed Event at the Onset of Reproduction

Abstract

The heat shock response (HSR) is essential for proteostasis and cellular health. In metazoans, aging is associated with a decline in quality control, thus increasing the risk for protein conformational disease. Here, we show that in C. elegans, the HSR declines precipitously over a 4 hr period in early adulthood coincident with the onset of reproductive maturity. Repression of the HSR occurs due to an increase in H3K27me3 marks at stress gene loci, the timing of which is determined by reduced expression of the H3K27 demethylase jmjd-3.1. This results in a repressed chromatin state that interferes with HSF-1 binding and suppresses transcription initiation in response to stress. The removal of germline stem cells preserves jmjd-3.1 expression, suppresses the accumulation of H3K27me3 at stress gene loci, and maintains the HSR. These findings suggest that competing requirements of the germline and soma dictate organismal stress resistance as animals begin reproduction.

Figure 1. Multiple stress responses collapse within the first 24 hours of adulthood

Stress gene expression relative to rpb-2 and cdc-42 in adult animals maintained at 15°C and subjected to control (c) conditions or (A) heat shock (HS) at 33°C for 30 min, (B) 100 μg/ml tunicamycin (Tun) for 3 hours (C) 200 mM paraquat (para) for 2 hours or (D) 800 μg/ml Ethidium Bromide (EtBr) for 8 hours. Values plotted are the mean of 4 experimental replicates and error bars denote SEM. Statistical significance was calculated using one-way ANOVA with Tukey post analysis comparison of groups.* p < 0.05, ** p < 0.01, *** p < 0.001. Statistical comparisons denote the largest p-value within each treatment group for each gene relative to day 1 treatment. See also figure S1.

Figure 2. The heat shock response and stress resistance decline within a 4 hour window at the onset of egg-laying

(A) Survival of animals at 35°C. (B) Thermorecovery of worms exposed to 33°C heat shock for 6 hours and allowed to recover at 20°C for 48 hours. (C and D) Survival of C. elegans exposed to (C) 200 mM paraquat or (D) 10 mM DTT as day 1 or 2 adults. (E) Schematic of prominent reproductive events spanning the transition from the end of the final larval (L4) stage to peak egg-laying. Time in hours should be multiplied by 1.5 or 0.7 to obtain approximate timing of events at 15°C and 25°C respectively (Hirsh et al., 1976). Values plotted in each panel are the mean of at least 4 experimental replicates. Error bars represent SEM. Statistical significance was calculated using one-way ANOVA with Tukey post analysis comparison of groups (B, F and G) or two-way ANOVA with Bonferroni post analysis comparison (A, C and D). * p<0.05, ** p <0.01, *** p <0.001, not significant (ns) p > 0.05. See also figure S2.

Figure 3. Altered chromatin landscape underlies collapse of the heat shock response

(A) hsf-1 expression relative to rpb-2 and cdc-42. (B) Confocal microscopy of HSF-1::GFP nuclear localization in hypodermal cells of day 1 (L4 + 4 hours) and day 2 (L4 + 28 hours) adults. Triangles and arrow heads highlight the nucleus and nucleolus respectively of select hypodermal cells. Scale bar = 10 μm. (C) HSF-1 gel shift assay using DNA Probes containing intact or mutant versions of the HSF-1 consensus binding motif (HSE). (D) Quantification of HSF-1 gel shift experiments. ChIP-qPCR on HSF-1::GFP worms using (E and F) anti-GFP or (G - I) anti RNA pol-II (ama-1) antibodies. For a schematic of the regions amplified see Fig.S3D. Values plotted are the mean of at least 4 biological replicates except in the case of panel D where means are from 3 independent experiments. Error bars represent SEM. Statistical significance was calculated by one-way ANOVA with Tukey post analysis comparison (A) or two-way ANOVA with Bonferroni post analysis comparison (D-I). * p < 0.05, ** p < 0.01, *** p < 0.001, not significant (ns) p > 0.05. See also figure S3.

Figure 4. Increased H3K27me3 and repression of heat shock gene induction is due to reduced jmjd-3.1 expression

(A) DNase I digestion of chromatin isolated from gon-2(q388ts) animals. Values are plotted as the relative degree of digestion compared to day 1 adults for each genomic region. (B and C) H3K27me3 ChIP-qPCR on gon-2(q388ts) worms. (D–F) H3K27me3 demethylase expression relative to rpb-2 in (D and E) wild type (WT) or (F) gon-2 (q388ts) worms. (G) H3K27me3 ChIP-qPCR in WT and jmjd-3.1(gk384) null mutants. Primers used were the same as those in HSF-1 and RNA pol-2 ChIP-qPCR experiments. Values plotted in panel A are the mean of at least 3 biological replicates. All other values plotted are the mean of at least 4 biological replicates and error bars represent SEM. Statistical significance was calculated by Student's t-test (A-D, F and G) or one-way ANOVA with Tukey post analysis comparison (E) * p <0.05, ** p <0.01, *** p <0.001, ns p > 0.05. TSS = Transcription start site. hsp-70p = promoter of C12C8.1. See also figure S4.

Figure 5. The timing of stress response decline and loss of stress resistance is controlled by jmjd-3.1

(A) hsp-70 (C12C8.1) and (B) hsp-16.11 expression in wild type (WT), jmjd-3.1 null and jmjd-3.1 over-expressing (o/e) worms exposed to control (c) or HS (33°C, 30 min) conditions. (C) Survival of day 1/day 2 WT (blue/orange), jmjd-3.1 null (red/purple) and jmjd-3.1 o/e (green/black) worms at 35°C. Day 2 WT vs day 2 jmjd-3.1 oe, p = 0.0022; day 1 WT vs day 1 jmjd-3.1 null, p = 0.0096. (D) Thermorecovery of WT, jmjd-3.1 null and jmjd-3.1 o/e animals. (E) hsp-4, (F) gcs-1 and (G) hsp-6 expression in WT, jmjd-3.1 null and jmjd-3.1 o/e worms exposed to control (c) conditions, 33°C heat shock (HS) for 30 min or 200 mM paraquat (para) for 2 hours. (H) Lifespan analysis at 20°C. WT (blue line), jmjd-3.1 null (red line) and jmjd-3.1 o/e (green line). WT vs jmjd-3.1 o/e, p = 0.0006. See table S1 and table S2 for all statistical comparisons. Values plotted are the mean of at least 4 independent experiments and bars represent SEM. Statistical significance was calculated by two-way ANOVA with Bonferroni post analysis comparison except in panel H where log-rank test was used. * p < 0.05, ** p < 0.01, *** p < 0.001. See also figure S5.

Figure 6. Removal of germ line stem cells maintains jmjd-3.1 expression, suppresses accumulation of H3K27me3 and restores transcription at heat shock genes

Expression of (A) hsp-70 (C12C8.1) and (B) hsp-16.11 in wild type, glp-1 (e2141ts) and glp-4 (bn2ts) mutants maintained at 25°C and exposed to control (c) or heat shock (HS) conditions during early adulthood. (C) Expression of jmjd-3.1 at different days of adulthood in wild type, glp-1 and glp-4 worms maintained at 25°C. (D) RNA pol-II (ama-1) or (E) H3K27me3 ChIP-qPCR in gon-2 and glp-1 animals maintained at 25°C. Values plotted are the mean of at least 4 biological replicates and error bars represent SEM. Statistical significance was calculated by one-way ANOVA (A-C) with Tukey post analysis comparison or two-way ANOVA with Bonferroni post analysis comparison (D and E). * p < 0.05, ** p < 0.01, *** p < 0.001. See also figure S6.

Figure 7. glp-1 mutants maintain the HSR, enhance stress resistance and increase lifespan through jmjd-3.1

(A) ChIP-qPCR of H3K27me3 at stress gene loci in day 2 adult glp-1(e2141ts) and glp-1(e2141ts);jmjd-3.1(gk384) animals. (B) HS gene expression in glp-1 and glp-1;jmjd-3.1 double mutant animals exposed to control or heat shock conditions at day 2 of adulthood. (C) Thermorecovery (at day 2 of adulthood), (D) thermotolerance (at day 2 of adulthood) and (E) lifespan analysis of wild type (N2) (blue line), glp-1 (red line) and glp-1;jmjd-3.1 (green line) worms raised at 25°C. For (D): glp-1 vs glp-1;jmjd-3.1, p = 0.0013; N2 vs jmjd-3.1(gk384), p = 0.081. For (E): Mean lifespan in days were N2, 12.67 +/− 0.35; glp-1, 15.61 +/− 0.46 and glp-1;jmjd-3.1, 14.2 +/− 0.28; glp-1 vs glp-1;jmjd-3.1(gk384), p = 0.0001. For all statistical comparisons see Tables S1 and S2. Values plotted are the mean of at least 3 independent experiments and error bars represent SEM. Statistical significance was calculated using Student's t-test (A and B), one-way ANOVA (C), two-way ANOVA (D) or log-rank test (E). * p < 0.05, ** p < 0.01, *** p < 0.001, ns p > 0.05. (F) Proposed model for programmed repression of the HSR. Thickness of blue arrows represents relative levels of transcription and intensity of circles represents relative protein levels. Cylinder (nucleosome) proximity represents chromatin accessibility. HSE = heat shock element, sHSP = small heat shock protein. See also figure S7.