Expression of insulin-like growth factors depends on both mass and resource availability in female green anoles (Anolis carolinensis)

The insulin and insulin-like signaling (IIS) network is an important mediator of cellular growth and metabolism in animals, and is sensitive to environmental conditions such as temperature and resource availability. The two main hormones of the IIS network, insulin-like growth factor 1 (IGF1) and insulin-like growth factor 2 (IGF2), are present in all vertebrates, yet little is known regarding the responsiveness of IGF2 in particular to external stimuli in non-mammalian animals. We manipulated diet (low quantity of food or high quantity of food) in adult green anole (Anolis carolinensis) females to test the effect of energetic state on hepatic gene expression of IGF1 and IGF2. The absolute expression of IGF2 in female green anoles is 100X higher than IGF1 regardless of diet treatment, and IGF1 and IGF2 expression interact with post-treatment body mass and treatment, as do the purported housekeeping genes glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and eukaryotic elongation factor 2 (EEF2). The Low Diet group showed a negative relationship between body mass and gene expression for all genes, whereas the relationships between body mass and gene expression in the High Diet group were either absent (in the case of IGF1) or positive (for all other genes). After accounting for total change in mass the Low Diet group expressed IGF2, GAPDH and EEF2 at higher levels compared to individuals in the High Diet group of similar ▵ mass. These results illustrate that expression of IGF1 and IGF2, and housekeeping genes are affected by energe­tic status in reptiles.