EXPRESSION OF SNAIL2, A 2ND MEMBER OF THE ZEBRAFISH SNAIL FAMILY, IN CEPHALIC MESENDODERM AND PRESUMPTIVE NEURAL CREST OF WILD-TYPE AND SPADETAIL MUTANT EMBRYOS

Transcripts of a newly discovered gene called snail2, encoding a zinc finger protein of the Snail family, first appear in rows of cephalic m esendodermal cells in gastrulating zebrafish embryos. At the end of ga strulation, snail2 RNA accumulates in a domain of ectodermal cells tha t mark the border between the epidermal epithelium and the neural plat e and includes precursors of the neural crest. During somitogenesis, s nail2 expression becomes restricted to neural crest. snail2 is thus on e of the earliest genes yet known to be specifically expressed in neur al crest in zebrafish embryos. Since snail2 is expressed in mesendoder m, a tissue layer whose convergence in the trunk is known to be altere d in embryos homozygous for the spadetail mutation, we examined snail2 expression in spadetail embryos. In these mutants, the number of ceph alic mesendodermal cells expressing snail2 is strongly reduced and the distribution of cells containing snail2 and no tail transcripts in th e axial mesoderm is much broader than normal. Moreover, the embryos ar e shorter than normal at the end of gastrulation. This shows that, in addition to the failure of paraxial mesoderm to converge normally in t he trunk during gastrulation, spadetail also affects the elongation of the embryo and the convergence of axial and lateral mesendoderm in bo th trunk and head. (C) 1995 Academic Press, Inc.