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. 2017 Feb 22;72(8):1033–1037. doi: 10.1093/gerona/glx017

Figure 1.

Figure 1.

Interindividual variation in gene expression and life span as a function of temperature. This figure shows that the amount of interindividual variation in three kinds of reporter gene expression, including a life-span biomarker, decreases at 25°C (B); interestingly, the amount of interindividual variation in life span also decreased at 25°C (D). Top graphs (A, B) depict mean ± SEM; bottom graphs (C, D) depict 95% confidence intervals (CI). To determine statistical significance, two-way analysis of variance (ANOVA) followed by the Holm–Sidak test for multiple comparisons was used for comparing the effects of temperature and strain on mean or CV, unless otherwise stated. CV is the coefficient of variation (SD/mean); CV is displayed as a whole-number percentage. Five independent trials consisting of approximately 500 individuals of each strain (one per reporter) at each temperature were used to generate the graphs of reporter gene expression. Fluorescence levels for animals expressing Pgpd-2::gfp are divided by 10 for plotting purposes; actual values are shown in Supplementary Table S1. (A) All reporters were significantly different in expression level from one another within each temperature. All p values from two-way ANOVA followed by Holm–Sidak testing for effects of strain and temperature on mean expression are shown in Supplementary File F1. Measured Pgpd-2::gfp expression was significantly different between 16°C and 20°C (p = .001) and 16°C and 25°C (p = .0003). Pvit-2::gfp was significantly different between 16°C and 20°C (p = .007). No significant differences were detected in induced Phsp-16.2::gfp expression between any temperatures; constitutive Phsp-16.2::gfp expression at 25°C was significantly different from all other gene expression levels at 25°C (p = .02, one-way repeated measures ANOVA, Student–Newman–Keuls test). Temperature had a significant effect on mean expression between 16°C and 20°C and between 16°C and 25°C, when the entire profile of reporters is considered (p = .00009 for 16°C vs 25°C and 16°C vs 20°C). Also, see Table 1. (B) Pvit-2::gfp CV was significantly greater than Phsp-16.2::gfp CV at 16°C (p = .011). Pgpd-2::gfp CV significantly changed between 20°C and 25°C (p = .0003). Pvit-2::gfp CV significantly changed between 16°C and 25°C (p = .008). CV measured for 25°C Phsp-16.2::gfp expression was significantly higher than for the 35°C -induced expression of Phsp-16.2::gfp (p = .02, paired t test). Temperature has a significant effect on CV of the analyzed reporters between 16°C and 25°C (p = .00028) and between 20°C and 25°C (p = .019); increasing temperature decreased worm-to-worm variation in gene expression. Explicit p values for every comparison from the two-way ANOVA followed by Holm–Sidak testing for effects of temperature and strain on CV are detailed in Supplementary File F2. Also, see Table 1. (C) Mean life span significantly decreased with increasing temperature; 95% CI shown. Fifty independent life-span experiments at various temperatures comprised the Life span × Temperature data set. Also, see Table 2. (D) Interindividual variation in life span significantly decreased at 25°C; 95% CI shown. Also, see Table 2. Raw data for life spans and individual life-span trial CVs is available in Supplementary File F3.