Meeting Abstract

P3-112   -   Seasonal changes in gene expression of steroidogenic enzymes in the ovary of red-sided garter snakes (Thamnophis sirtalis parietalis) Barlowe, ML*; Lincoln, JM; Rucker, HR; Thomas, RL; Parker, MR; James Madison University; James Madison University; James Madison University, University of Arizona; James Madison University; James Madison University barlowml@dukes.jmu.edu

Sex steroid hormones are vital regulatory signals in vertebrate reproduction, but despite this, the natural variation in steroidogenic enzyme expression is not described for most vertebrates. Many temperate species of vertebrates have shortened breeding seasons, and how steroidogenesis has adapted to temporal constraint can inform predictions of species responses to climate change. The red-sided garter snake (Thamnophis sirtalis parietalis) exhibits a dissociated reproductive pattern where gametogenesis and circulating sex steroid hormone levels are uncoupled. The sexes also have divergent patterns: males have highest circulating androgens in fall while females show increased circulating estradiol primarily in spring for ~24h post-copulation and possibly a slower increase toward summer. To identify the enzymes responsible for the female pattern, we focused on four steroidogenic enzymes: StAR, Cyp17α1, 17βHSD3, and Cyp19α1 (aromatase). We designed primers for each enzyme using the Thamnophis genome in NCBI and validated them via traditional PCR. We will use qPCR to quantify mRNA expression from ovarian tissue collected from females across spring, summer, and fall. We predict aromatase and StAR expression will be elevated in spring and summer. Aromatase is the terminal step in estrogen synthesis and should match when circulating levels are elevated, and the same is true for StAR, the rate-limiting enzyme. Studies on other reptiles found Cyp17α1 and 17βHSD3 expression were generally lower when StAR expression was high, and we thus predict Cyp17α1 and 17βHSD3 will be low in spring and summer. In most wild vertebrates, seasonal shifts in steroid synthesis are inferred based on observations of circulating hormone concentrations, but knowledge of which enzymes are dynamically expressed could reveal evolutionary patterns previously unappreciated.