Dorsal differentiation of neural plate cells induced by BMP-mediated signals from epidermal ectoderm

The segment polarity gene hedgehog (hh) encodes a novel signaling protein that mediates local cell-cell interactions in the developing Drosophila embryo. Here we describe the existence of an hh-related gene family in the zebrafish, Brachydanio rerio. One of these genes, sonic hedgehog (shh), is expressed in the notochord, floor plate, and posterior fin mesoderm, tissues associated with polarizing activities in various vertebrate embryos. The pattern of shh expression in zebra-fish mutants affecting axial structures, together with the consequences of its ectopic expression in normal embryos, is consistent with a role for shh in floor plate induction. By expressing shh in transgenic Drosophila embryos, we also demonstrate a strong functional conservation between the fish and fly hh genes.

Slug, a vertebrate gene encoding a zinc finger protein of the Snail family, is expressed in the neural crest and in mesodermal cells emigrating from the primitive streak. Early chick embryos were incubated with antisense oligonucleotides to chick Slug. These oligonucleotides specifically inhibit the normal change in cell behavior that occurs at the two sites in the emerging body plan in which the gene is expressed. This change, which is the transition from epithelial to mesenchymal character, occurs at the formation of mesoderm during gastrulation and on emigration of the neutral crest from the neural tube.