Expression of ovarian 20 alpha-hydroxysteroid dehydrogenase in rat thymus

Ovarian 20 alpha -hydroxysteroid dehydrogenase (20 alpha -HSD), which conve rts progesterone to a derivative devoid of biological activity, plays a cru cial role in achieving the short estrous cycle in rats. Although 20 alpha - HSD activity has also been demonstrated in the thymus, its molecular nature , function, and regulation of expression have yet to be determined. In the present study we investigated if 20 alpha -HSD activity in the thymus origi nates in a transcript identical to that expressed in the ovary. RT-PCR anal ysis indicated the expression of 20a-HSD mRNA in rat thymus, and sequencing of the PCR product showed 100% identity to ovarian 20 alpha -HSD cDNA. Imm unohistochemical study using anti-rat ovarian 20 alpha -HSD antibody demons trated the expression of 20 alpha -HSD protein in the thymus. The 20 alpha -HSD-expressing cells in the thymus seemed to be some type of lymphocyte by their morphology. These results suggest that the same molecular species as ovarian 20 alpha -HSD is expressed in thymic lymphocytes. Therefore, 20 al pha -HSD may play a role in T-lymphocyte proliferation and differentiation processes.