The closely related POU family transcription factors Brn-3a and Brn-3b areexpressed in distinct cell types in the testis

Although the Brn-3a and Brn-3b POU family transcription factors were origin ally identified in neuronal cells, their expression in some non neuronal ce ll types has previously been reported. Here we report that Brn-3a and Brn-3 b are also expressed in the testis with expression of each factor being obs erved at distinct stages of germ cell development. Thus, Brn-3a is expresse d in spermatogonia whereas Brn-3b expression is observed in post-meiotic sp ermatids. In agreement with this, Brn-3a expression is detectable much earl ier than that of Brn-3b in testes derived from sexually immature postnatal animals. Similarly, Brn-3b expression is absent in knock out mice lacking a functional CREM transcription factor in which the later stages of germ cel l development do not occur, whereas Brn-3a expression is observed at simila r levels in the testes of these knock out mice. Interestingly, the cellular pattern of Brn-3a expression during germ cell development coincides with t hat of the BRCA-1 anti-oncogene. Consistent with the possibility that Brn-3 a may regulate expression of BRCA-1 in the testis, we have shown that Brn-3 a can strongly activate the BRCA-1 promoter in co-transfection experiments whereas Brn-3b does not have this effect. Hence, as observed in neuronal ce lls, Brn-3a and Brn-3b may play distinct and important functional roles in the regulation of gene expression during germ cell development. (C) 2001 El sevier Science Ltd. All rights reserved.