Cooperation of endoderm-derived BMP2 and extraembryonic ectoderm-derived BMP4 in primordial germ cell generation in the mouse

The primordial germ cells (PGCs) of the mouse are derived from proximal epi blast cells that are adjacent to the extraembryonic ectoderm during gastrul ation. Previous studies have demonstrated that extraembryonic ectoderm-deri ved BMP4 and BMP8B are both required for PGC generation. Here we show that Bmp2, a member of the Dpp class of the Bmp superfamily, also plays a role i n PGC generation. PGC number is significantly reduced in Bmp2 heterozygous and homozygous embryos at the N2 generation onto C57BL/6, background. Bmp2 homozygous embryos also have a short allantois and about 50% of them do not undergo normal chorioallantoic fusion. Using whole-mount in situ hybridiza tion, we show that Bmp2 is primarily expressed in the endoderm of mouse pre gastrula and gastrula embryos. Using a genetic approach, we further show th at Bmp2 and Bmp4, but not Bmp2 and Bmp8b, have an additive effect on PGC ge neration. These results suggest that PGC generation in the mouse embryo is regulated not only by extraembryonic ectoderm-derived BMP4 and BMP8B, but a lso by endoderm-derived BMP2. (C) 2001 Academic Press.