Fig. 4.

Transcriptional modules of coregulated genes are associated with muscle phenotype in deer mice. A: histological analyses revealed that the gastrocnemius muscle of high-altitude deer mice has a higher capillary density (top) and a higher areal density of oxidative fibers (bottom) relative to that of low-altitude mice. B: Left: transcripts that are differentially expressed between high- and low-altitude populations of deer mice (n = 68 transcripts) cluster into two discrete modules (P1 and P2). Right: transcripts that are differentially expressed between mice in different rearing environments (wild-caught mice sampled at their native elevations vs. F1 lab-reared mice, n = 658 transcripts) cluster into five modules (T1–T5). C: Left: changes in expression of the P2 module (50 transcripts) are significantly associated with evolved (nonplastic) differences in muscle capillary density between high- and low-altitude deer mice (r² = 0.46, P = 0.001). Right: changes in expression of the T5 module (224 transcripts) are associated with environmentally induced (plastic) changes in the density of oxidative fibers in the gastrocnemius (r² = 0.30, P = 0.007). For each transcriptional module, an index of overall expression is provided by PC1 scores, where PC1 is the first axis of a principal components analysis on the correlation matrix of transcript abundance for all genes in a given module. In both panels, data points for high- and low-altitude mice are denoted as solid and open symbols, respectively. [Adapted with permission from Fig. 1 of Ref. 169: Adaptive modifications of muscle phenotype in high-altitude deer mice are associated with evolved changes in gene regulation. Scott GR, et al., Mol Biol Evol doi:10.1093/molbev/msv076].