AN ANDROGEN-REGULATED HOMEOBOX GENE EXPRESSED IN RAT TESTIS AND EPIDIDYMIS

Homeobox genes encode DNA-binding proteins that regulate the transcrip tion of subordinate downstream genes. In this study, we show that the Pem homeobox gene is expressed and regulated in a unique manner in neo natal and adult rats. Pem gene expression was primarily confined to re productive tissue: epididymis, testis, ovary, and placenta. In the epi didymis, Pem transcripts were localized by in situ hybridization analy sis to the proximal cauda region, a site where spermatozoa gain fertil ization competence. Pem mRNA levels dramatically increased between Day s 21 and 26 postpartum in the epididymis, coincident with the inductio n of genes known to be responsive to testosterone (T), but in contrast to that of other genes examined, including the Hoxc-8 homeobox gene. Pem expression was shown to be T-dependent on the basis of an absence of Pem transcripts in the epididymides of hypophysectomized rats and r estoration of normal Pem mRNA levels after administration of T. In the testis, Pem mRNA levels were elevated earlier (between Days 12 and 15 postpartum) and less dramatically than in epididymis. Pem gene expres sion in the testis was depressed after hypophysectomy, but normal leve ls of Pem expression were not restored by T treatment under the same c onditions that permitted normal Pem expression in the epididymis. To o ur knowledge Pem is the first reported putative transcription factor t hat has been demonstrated to depend on androgens for expression in the epididymis, and thus Pem is a candidate as a regulator of androgen-de pendent events in this tissue.