13-P076 Retinoic acid and FGF signals pattern the LPM in the post-gastrula Xenopus embryo

The axial tissues of the vertebrate embryo is a term that refers collectively to the floor plate (a cell population that lies at the ventral floor of the neural tube) and the notochord (which is a mesodermal rod of cells located immediately ventral to the floor plate). The notochord and floor plate both secrete the morphogen signal Sonic Hedgehog (Shh) that patterns the dorsoventral axis of the neural tube. Moreover the ability of both tissues to induce floor plate differentiation is mediated by Shh. These two tissues are believed to derive from a common progenitor pool which is located in Hensen’s node in the chick embryo. Hensen’s node develops at the anterior tip of the primitive streak. Some of these progenitor cells remain in the node as resident stem cells. It is unclear how the progenitor cells in Hensen’s node become committed to either the notochord or floor plate cell fate. The Notch signalling pathway is a key player in binary cell fate choice in numerous other developmental contexts in the developing vertebrate and invertebrate embryo and we have found this pathway plays a role in the cell fate decision that occurs in the axial tissue precursors in Hensen’s node. We also show that Notch signalling modulates the response of neural cells to the morphogen Shh.