A HEMEOBOX GENE ESSENTIAL FOR ZEBRAFISH NOTOCHORD DEVELOPMENT

The notochord is a midline mesodermal structure with an essential patt erning function in all vertebrate embryos. Zebrafish floating head (fl h) mutants lack a notochord, but develop with prechordal plate and oth er mesodermal derivatives, indicating that flh functions specifically in notochord development. We show that floating head Is the zebrafish homologue of Xnot, a homeobox gene expressed In the amphibian organize r and notochord. We propose that flh regulates notochord precursor cel l fate.