Smad5 is required for mouse primordial germ cell development

Smad5, together with Smad1 and Smad8, have been implicated as downstream si gnal mediators for several bone morphogenetic proteins (BMPs). Recent studi es have shown that primordial germ cells (PGCs) are absent or greatly reduc ed in Bmp4 or Bmp8b mutant mice. To define the role of Smad5 in PGC develop ment, we examined PGC number in Smad5 mutant mice by Oct4 whole-mount in si tu hybridization and alkaline phosphatase staining. We found ectopic PGC-li ke 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 f actor involved in PGC generation and localization. (C) 2001 Elsevier Scienc e Ireland Ltd. All rights reserved.