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

Abstract

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.

Development of male-larger sexual size dimorphism in a lizard: IGF1 peak long after sexual maturity overlaps with pronounced growth in males

“…The liver was chosen as the target tissue because estrogen and testosterone metabolize in the organ while gonads were too small. Furthermore, the liver was also chosen as it had a higher expression of IGF1 and IGF2 than other tissues in several reptiles ( Reding et al, 2016 ; Duncan et al, 2020 ; Marks et al, 2021 ), and differences in the expression of IGF1R/IGF2R in the liver were found between fast versus slow-growing sexually dimorphic snake ( Reding et al, 2016 ). After dissection, the liver samples were quickly cut into small pieces and stored in RNA later (Sigma-Aldrich Inc., Missouri, United States) at −20°C until used for RNA extraction.…”

“…We selected four reference genes based on previous experimental work. Glyceraldehyde 3-phosphate dehydrogenase ( GAPDH ) has been used in mammals and reptiles ( Coulson et al, 2008 ; Sanger et al, 2014 ) with limits under caloric restrictions ( Gong et al, 2016 ; Marks et al, 2021 ). The 18S ribosomal RNA genes ( 18S ) had a primer pair already validated previously in reptiles ( Plot et al, 2012 ; Rollings et al, 2017 ).…”

“…IGF1 and its counterpart IGF2 have roles in cell growth and proliferation as they are mediators of the growth hormone action ( Schwartz and Bronikowski, 2016 ). The role of IGF1 and IGF2 in the growth of reptiles has been well documented ( Reding et al, 2016 ; Beatty and Schwartz, 2020 ; Duncan et al, 2020 ; Marks et al, 2021 ). IGF1 has been assumed to be a postnatal growth factor and IGF2 to be a prenatal growth factor, but this assumption has been challenged in reptiles ( Beatty and Schwartz, 2020 ).…”

“…IGF1 and IGF2 compete to bind to insulin receptors and IGF1R which have a role in cell proliferation and growth ( Denley et al, 2005 ; Schwartz and Bronikowski, 2016 ). IGF1 plasma levels have also been associated with reproduction ( Guillette et al, 1996 ; Sparkman et al, 2010 ), and its gene expression is affected by nutrition in reptiles ( Duncan et al, 2015 ; Marks et al, 2021 ). The role of IGF1 in growth in humans and mice is best transcribed in its role in postnatal bone elongation.…”

Conserved and convergent mechanisms underlying performance–life-history trade-offs

“…Despite the emphasis placed on homology with regard to ILS, it is noteworthy that our understanding of various functional aspects of IGF signaling (and IGFBPs in particular) is derived primarily from work on humans, mice or rats, despite important interspecific variation in the action of key components of ILS. For example, IGF-2 is both paternally imprinted and not produced post-natally in mice (Carter et al, 2002); however, the IGF2 gene is not only expressed in adult reptiles without imprinting (Schwartz and Bronikowski, 2016), but in green anole females it is also expressed at higher levels in calorie-restricted animals compared with controls (Marks et al, 2021). The implications for performance are currently unknown, and we still have much to learn about the action of these important signaling molecules that might affect investment in growth and reproduction versus survival in different species.…”