BMP signalling regulates the development of many cell types throughout embryogenesis. Now, Miura and colleagues report that it is required during gastrulation for the development of the paraxial mesoderm, which forms the connective tissues of the back (see ). To investigate BMP signalling during gastrulation, the researchers deleted Bmpr1a (which encodes a receptor for BMP2 and BMP4) in some epiblast cells of mouse embryos. Whereas Bmpr1a-null embryos fail to initiate gastrulation, in these mosaic embryos gastrulation begins normally but then recruitment of prospective paraxial mesoderm to the primitive streak becomes delayed. As a result, cells with paraxial mesoderm character form both in the middle of the streak and at the anterior end where they normally form;strikingly, multiple columns of somites develop as a result. Inhibition of FGF signalling, however, restores the timing of prospective paraxial mesoderm recruitment and partly rescues somite development. The researchers conclude,therefore, that BMP and FGF signalling function antagonistically during the development of paraxial mesoderm.
