EVIDENCE THAT MOTHERS-AGAINST-DPP-RELATED-1 (MADR1) PLAYS A ROLE IN THE INITIATION AND MAINTENANCE OF SPERMATOGENESIS IN THE MOUSE

We have cloned a mouse cDNA encoding a Mothers-against-dpp (MAD)-relat ed protein, MADR1. Madr1 is ubiquitously expressed in the mouse embryo , indicating a broad function in a variety of tissues during embryogen esis, potentially relaying signals of numerous BMPs. However, its expr ession in the testis is strictly germ cell-specific and developmentall y regulated. Testicular Madr1 expression starts in some seminiferous t ubules at 2 weeks of age. After mid-puberty, a stage-specific Madr1 ex pression is established. During the cycling of the seminiferous epithe lium, Madr1 expression initiates in the pachytene spermatocytes of sta ge V seminiferous tubules, peaks at stage X, then decreases as pachyte ne spermatocytes differentiate into secondary spermatocytes and then r ound spermatids. In the testis of adult Bmp8b homozygous mutant males, the Madr1-expressing pachytene spermatocytes are the first cell popul ation to show increased apoptosis. These data suggest that MADR1 serve s as a downstream component of the BMP8 signaling pathway during the d ifferentiation of meiotic male germ cells. (C) 1997 Elsevier Science i reland Ltd.