Requirement of Bmp8b for the generation of primordial germ cells in the mouse

Smad5 is required for mouse primordial germ cell development

Smad5, together with Smad1 and Smad8, have been implicated as downstream signal mediators for several bone morphogenetic proteins (BMPs). Recent studies have shown that primordial germ cells (PGCs) are absent or greatly reduced in Bmp4 or Bmp8b mutant mice. To define the role of Smad5 in PGC development, we examined PGC number in Smad5 mutant mice by Oct4 whole-mount in situ hybridization and alkaline phosphatase staining. We found ectopic PGC-like cells in the amnion of some Smad5 mutant mice, however, the total number of PGCs was greatly reduced or completely absent in Smad5 mutant embryos, similar to Bmp4 or Bmp8b mutant embryos. Therefore, Smad5 is an important factor involved in PGC generation and localization.

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 epiblast cells that are adjacent to the extraembryonic ectoderm during gastrulation. Previous studies have demonstrated that extraembryonic ectoderm-derived 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 in 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 hybridization, we show that Bmp2 is primarily expressed in the endoderm of mouse pregastrula and gastrula embryos. Using a genetic approach, we further show that Bmp2 and Bmp4, but not Bmp2 and Bmp8b, have an additive effect on PGC generation. These results suggest that PGC generation in the mouse embryo is regulated not only by extraembryonic ectoderm-derived BMP4 and BMP8B, but also by endoderm-derived BMP2.

Detection of multiple bone morphogenetic protein messenger ribonucleic acids and their signal transducer, Smad1, during mouse decidualization

Decidualization is a process characterized by morphological and functional changes in the uterine stromal cells. In addition to steroid hormones, growth factors are implicated in this process. Using in situ hybridization, we found that mRNAs for several bone morphogenetic proteins (BMPs) were detected in the decidual and vascular endothelial cells. The Bmp7 mRNA was detected in the decidualizing stromal cells surrounding the blastocyst and distributed in a gradient, with the highest levels occurring near the uterine epithelium at 4.5 days post-coitus (dpc). With the progression of decidualization, Bmp7 signals in the deciduum at the antimesometrial side decreased, but strong signals were retained in the decidual area at the mesometrial side at 7.0 dpc. In contrast, Bmp8a transcripts increased from 5.5 to 7.0 dpc in the decidual tissue, with the highest levels occurring in the secondary decidual zone at the antimesometrial side. The Bmp2, Bmp4, and Smad1 transcripts were found in the secondary decidual zone, especially at the mesometrial side. The Bmp2 signals were primarily detected in decidual cells, whereas Bmp4 and Smad1 transcripts were mainly detected in vascular endothelial cells, suggesting that they may be involved in decidual angiogenesis.