Xmc mediates Xctr1‐independent morphogenesis in Xenopus laevis

In the frog, Xenopus laevis , fibroblast growth factor (FGF) signaling is required for both mesoderm formation and the morphogenetic movements that drive the elongation of the notochord, a dorsal mesodermal derivative; the coordination of these distinct roles is mediated by the Xenopus Ctr1 (Xctr1) protein: maternal Xctr1 is required for mesodermal differentiation, while the subsequent loss of Xctr1 promotes morphogenesis. The signaling cascade activated by FGF in the presence of Ctr1 has been well characterized; however, the Xctr1‐independent, FGF‐responsive network remains poorly defined. We have identified Xenopus Marginal Coil ( Xmc ) as a gene whose expression is highly enriched following Xctr1 knockdown. Zygotic initiation of Xmc expression in vivo coincides with a decrease in maternal Xctr1 transcripts; moreover, Xmc loss‐of‐function inhibits Xctr1 knockdown‐mediated elongation of FGF‐treated animal cap explants, implicating Xmc as a key effector of Xctr1‐independent gastrular morphogenesis. Developmental Dynamics 238:2382–2400, 2009. © 2009 Wiley‐Liss, Inc.