We wanted to know whether regulation was conserved across evolution. Specifically, we wanted to know if a gene that was found to be age regulated in one species was also age regulated in other species. To investigate this, we compared patterns of gene expression in aging time course data from C. elegans (Lund et al. 2002) and D. melanogaster (Pletcher et al. 2002) to the data in the human kidney. In order to ascertain whether aging proceeds similarly across species, we first needed to identify orthologous sets of genes in worms, flies and humans. Our criterion for an ortholog pair is that they exhibit best reciprocal BLAST hits between species. Beginning with the set of 447 age-regulated genes in the human kidney, we identified 119 worm and 142 fly orthologs. From the set of 167 age-regulated genes in the worm, we identified 60 human orthologs, and similarly, from 1264 age-regulated genes in the fly, we identified 465 human orthologs.
We plotted the regression coefficients for the ortholog pairs in the human and worm aging time courses in a scatter plot. Similarly, we plotted the regression coefficients for the ortholog pairs in the human and fly time courses (Sup. Figs. 2A,2B). We then calculated Pearson correlations for the set of ortholog pairs. Overall, we saw no correlation between age-regulation of gene expression between human and either fly or worm. Specifically, the age-regulated human genes paired with fly orthologs show a Pearson correlation of r = -0.05 (p = 0.27). The age-regulated fly genes paired with human orthologs show a Pearson correlation of r = -0.05 (p = 0.12). The age-regulated human genes paired with worm orthologs show a Pearson correlation of r = 0.05 (p=0.54). The age-regulated worm genes paired with human orthologs show a Pearson correlation of r= -0.01 (p = 0.08). These results show no evidence for overlap in the aging process between different species.