EVIDENCE THAT MOUSE BMP8A (OP2) AND BMP8B ARE DUPLICATED GENES THAT PLAY A ROLE IN SPERMATOGENESIS AND PLACENTAL DEVELOPMENT

We have identified two highly conserved mouse genes encoding bone morp hogenetic protein 8A (BMP8A/OP2) and 8B (BMP8B). The two loci are tigh tly linked on chromosome 4, suggesting that they arose through a recen t gene duplication. Contrary to previous reports, neither gene is expr essed in the early postimplantation mouse embryo (7.5-10.5 days post c oitum) as judged by a variety of sensitive techniques. By contrast, hi gh levels of Bmp8a RNA are found in the decidual cells of the uterus, and both genes are expressed in the trophoblast cells of the labyrinth ine region of the placenta and in the inner root sheath of hair follic les of early postnatal skin. In addition, both Bmp8a and Bmp8b are exp ressed in the testis during specific stages of spermatogenesis, with t he highest levels of RNA in stage 6-8 round spermatids after 3 weeks o f age. Bmp8a and 8b are, therefore, the first members of the transform ing growth factor beta (TGF beta)-related gene family to be found expr essed in the germ cells of the testis, rather than in the somatic Sert oli cells. These results suggest that Bmp8a and 8b are not required fo r development of the embryo proper but regulate aspects of cell prolif eration, survival and/or differentiation during spermatogenesis and pl acentation.