STRUCTURE OF THE ZEBRAFISH SNAIL1 GENE AND ITS EXPRESSION IN WILD-TYPE, SPADETAIL AND NO TAIL MUTANT EMBRYOS

Mesoderm formation is critical for the establishment of the animal bod y plan and in Drosophila requires the snail gene. This report concerns the cloning and expression pattern of the structurally similar gene s nail1 from zebrafish. In situ hybridization shows that the quantity of snail1 RNA increases at the margin of the blastoderm in cells that in volute during gastrulation. As gastrulation begins, snail1 RNA disappe ars from the dorsal axial mesoderm and becomes restricted to the parax ial mesoderm and the tail bud. snail1 RNA increases in cells that defi ne the posterior border of each somite and then disappears when somiti c cells differentiate. Later in development, expression appears in cep halic neural crest derivatives. Many snail1-expressing cells were miss ing from mutant spadetail embryos and the quantity of snail1 RNA was g reatly reduced in mutant no tail embryos. The work presented here sugg ests that snail1 is involved in morphogenetic events during gastrulati on, somitogenesis and development of the cephalic neural crest, and th at no tail may act as a positive regulator of snail1.