Abstract: 485

SEASONAL CHANGES IN HEPATIC PROGESTERONE RECEPTOR mRNA AND VITELLOGENIN mRNA IN THE FRESH WATER TURTLE, Chrysemys picta.

Noemi Custodia¹ , Ian Callard^{1 *}
Boston University, Boston, MA ¹

Here we investigate the tissue expression and regulation of progesterone receptor and vitellogenin mRNA in the liver. Previous studies in the fresh water turtle Chrysemys picta have demonstrated that progesterone inhibits estradiol-induced vitellogenin secretion in this species. The action is probably direct, as we have also identified both PRA and PRB in the liver of this species. Further, there is evidence for the differential expression of PRA and PRB protein in the liver and oviduct during the turtle seasonal cycle. These changes correlate with the regulation of physiological events such as hepatic vitellogenesis and oviduct processing of fertilized eggs. Using turtle PR and Vtg cDNAs, we report seasonal changes in PR mRNA and vitellogenin (Vtg) mRNA in the liver. PR mRNA (4.5 Kb) is always present, but varies during the annual cycle, being highest when vitellogenesis is inhibited (winter/summer). Vtg mRNA is not present during winter, is highest during vitellogenesis in the spring, cannot be detected in summer and reappears during the fall period of vitellogenesis and ovarian recrudescence. These changes correspond well with previously reported vitellogenin protein levels as determined in this laboratory by homologous radioimmunoassay. These studies are supportive of a role for P in the seasonal regulation of hepatic vitellogenesis. Since a smaller PR gene transcription product (3.7Kb) representing PRA was not found, and both PRB and PRA have been identified in the turtle liver, it appears that the ratio of PRB/PRA is controlled at the translational level in the turtle, as in bird. Supported by NIH grants #RR06633 and #ES07381 to IPC.

    This abstract is being presented on Tuesday, August 3 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.