EVANS, A.E.*; NUNEZ, B.S.; University of Texas Marine Science Institute: Control of the steroidogenic acute regulatory protein (StAR) by osmoregulatory hormones in the euryhaline Atlantic stingray, Dasyatis sabina

Our laboratory is investigating the hormonal control of osmoregulation in the euryhaline elasmobranch Dasyatis sabina (Atlantic stingray). As demonstrated in other vertebrates, it is likely that D. sabina osmoregulatory hormones elicit many of their effects by stimulating the synthesis of the elasmobranch mineralocorticoid (1α-hydroxycorticosterone; 1α-B), which subsequently acts as an antinatriuretic factor. In mammals, steroidogenesis in adrenocortical cells is regulated by the expression and activity of the steroidogenic acute regulatory protein (StAR). StAR facilitates the rapid delivery of cholesterol to side chain cleavage, which converts cholesterol to pregnenolone. To better define the role of StAR in elasmobranch osmoregulation, we used degenerate primers in RT-PCR and RACE to isolate StAR mRNA sequence from the interrenal gland of D. sabina. Total RNA was isolated from a suite of tissues obtained from freshwater (FW) and saltwater (SW) adapted D. sabina to determine the effect of salinity on the tissue-specific expression of the elasmobranch StAR gene. StAR is expressed in the interrenal gland and heart of both FW and SW adapted D. sabina. Preliminary evidence from quantitative PCR suggests that StAR mRNA in the ventricle and interrenal gland is regulated by changes in salinity. Local production of mineralocorticoids (MC) in target tissues has been established in mammals; our research suggests similar MC production in the elasmobranch heart in response to osmotic challenges. Additional experiments examining the in vitro production of 1α-B in D. sabina are currently underway in our laboratory to better define the osmoregulatory role of StAR in the elasmobranch heart and interrenal gland.