BMP's repress WNT signaling to maintain stable stem cell populations. BMPR1A null mice died at embyonic day 8.0 without mesoderm specification, demonstrating its vital role in gastrulation. It has been demonstrated in experiments using dominant negative BMPR1A chick embryos that BMPR1A plays a role in apoptosis and adipocyte development. Using constitutively active forms of BMR1A it has been shown that it plays a role in cell differentiation. Signals tranduced by the BMPR1A receptor are not essential for osteoblast formation or proliferation; however, BMPR1A is necessary for the extracellular matrix depostition by osteoblasts. In the chick embryo, BMPR1A receptors are found in low levels in limb bud mesenchyme, a differing location to BMPR1B, supporting the differing roles they play in osteogenesis.