Seasonal regulation of steroidogenic enzyme expression within the green anole lizard (Anolis carolinensis) brain and gonad

Steroid hormones, such as testosterone and estradiol, are necessary for reproductive behavior. Seasonally breeding animals have increased sex steroid hormone levels during the breeding compared to non-breeding season, with increased reproductive behaviors and altered brain morphology in breeding individuals. Similar to other seasonally breeding animals, green anole lizards (Anolis carolinensis) have high sex steroid hormone levels and increased reproductive behaviors in the breeding season. Relatively less is known regarding the regulation of steroidogenesis in reptiles and this experiment examined whether enzymes involved in sex steroid hormone synthesis vary seasonally within the brain and gonads in wild-caught anole lizards. Specifically, we examined mRNA expression of steroidogenic acute regulatory protein (StAR), P450 17α-hydroxylase/C17-20lyase (Cyp17α1), 17 beta-hydroxysteroid dehydrogenase type 3 (17βHSD 3), and aromatase (Cyp19α1). We found that the mRNA for each of these genes was expressed in the lizard brain. Interestingly, Cyp19α1 mRNA expression in the brain was increased during the non-breeding season, potentially revealing a role for aromatase expression in the non-breeding brain. In the anole gonads, StAR mRNA expression levels were increased in both males and females during the breeding season, while the mRNA expression levels of CYP17α1 and 17βHSD 3 are increased when StAR mRNA expression was decreased, suggesting that the enzymes in the steroidogenic pathway are potentially regulated independently of StAR. This work reveals the seasonal regulation of steroidogenesis in the reptilian brain and gonad, although more work is necessary to determine the regulatory mechanisms that control these expression patterns.