SONIC HEDGEHOG IS NOT REQUIRED FOR THE INDUCTION OF MEDIAL FLOOR PLATE CELLS IN THE ZEBRAFISH

Sonic hedgehog (Shh) is a secreted protein that is involved in the org anization and patterning of several tissues in vertebrates. We show th at the zebrafish sonic-you (syu) gene, a member of a group of five gen es required for somite patterning, is encoding Shh, Embryos mutant for a deletion of syu display defects in patterning of the somites, the l ateral floor plate cells, the pectoral fins, the axons of motorneurons and the retinal ganglion cells, In contrast to mouse embryos lacking Shh activity, syu mutant embryos do form medial floor plate cells and motorneurons, Since ectopic overexpression of shh in zebrafish embryos does not induce ectopic medial floor plate cells, we conclude that sh h is neither required nor sufficient to induce this cell type in the z ebrafish.