The role and regulation of GDF11 in Smad2 activation during tailbud formation in the Xenopus embryo.

A key role for phosphorylation of Smad2 by TGFβ superfamily ligands in the axial patterning of early embryos is well established. The regulation and role of Smad2 signaling in post-neurula embryonic patterning, however, is less well understood. While a variety of TGFβ superfamily ligands are implicated in various stages of anterior-posterior patterning, the ligand GDF11 has been shown to have a particular role in post-gastrula patterning in the mouse. Mouse GDF11 is specifically localized to the developing tail and is essential for normal posterior axial patterning. Mature GDF11 ligand is inhibited by its own prodomain, and extracellular proteolysis of this prodomain is thought to be necessary for GDF11 activity. The contribution of this proteolytic regulatory mechanism to Smad activation during embryogenesis in vivo, and to the development of posterior pattern, has not been characterized. We investigate here the role of Xenopus GDF11 in the activation of Smad2 during the development of tailbud-stage embryos, and the role of this activation in larval development. We also demonstrate that the activity of BMP-1/Tolloid-like proteases is necessary for the normal GDF11-dependent activation of Smad2 phosphorylation during post-gastrula development. These data demonstrate that GDF11 has a central role in the activation of Smad2 phosphorylation in tailbud stage Xenopus embryos, and provide the first evidence that BMP-1/Tolloid-mediated prodomain cleavage is important for activation of GDF11 in vivo.