View Program - 2022 Population, Evolutionary, and Quantitative Genetics Conference

The insulin and insulin-like signaling (IIS) network plays an important role in mediating several life-history traits, including growth, reproduction, and senescence. In vertebrates there are two paralogous receptors (IGF1R and INSR) and three paralogous hormones (IGF1, IGF2, and Insulin) that can bind the receptors with varying affinities and these relationships are likely co-evolving across the vertebrate phylogeny. Along with evaluating the sequence variation, evolution of expression patterns are also important for understanding these co-evolutionary relationships. Although IGF1 and IGF2 are both key hormones in the vertebrate IIS network, research on IGF2 in juveniles and adults has been largely neglected because early biomedical research on rodents found negligible IGF2 postnatal expression. Our previous research on gene expression in this system found that lizards express IGF2 throughout life, and IGF1R was expressed at a much lower level than INSR – in stark contrast to biomedical rodents. Here, we challenged these assumptions of IGF2 and IGF1R expression being consistent across the phylogeny. Primarily, we ask to what degree IGF2 is expressed during postnatal life across amniotes (reptiles and mammals) by quantifying the relative gene expression of IGF1 and IGF2 using publicly available RNAseq data for 82 amniote species and quantitative polymerase chain reaction on liver cDNA at embryonic, juvenile and adult stages for two lizard, bird and mouse species. The results we will present indicate that (i) IGF2 is expressed postnatally across amniote species and life stages—often at higher relative expression level than IGF1, contradicting rodent models; (ii) the lack of rodent postnatal IGF2 expression is due to phylogenetic placement, not inbreeding or artificial selection; and (iii) adult IGF2 expression is sex-biased in some species. These results demonstrate that IGF2 expression is typical for amniotes throughout life, suggesting that a comprehensive understanding of the mechanisms mediating variation in life-history traits will require studies that measure both IGFs, since each can bind both receptors (IGF1R and INSR). We are furthering this research in understanding the relative expression patterns of the receptors (IGF1R and INSR) across the amniote phylogeny that will be incorporated into this discussion of the evolution of these hormone receptor relationships across amniotes.

Evolution of gene expression patterns of paralogous hormones (IGF1 and IGF2) and paralogous receptors (IGF1R and INSR) across amniotes.