Structure and distribution of N-cadherin in developing zebrafish embryos: morphogenetic effects of ectopic over-expression.

N-cadherin cDNA was cloned from a zebrafish embryonic cDNA library. Analysis of the deduced amino acid sequence of this molecule (ZN-cadherin) revealed a high degree of homology to N-cadherins of other species, except that its pre-sequence is considerably shorter. Nevertheless, following transfection into chinese hamster ovary (CHO) cells, the expressed protein was functionally active, namely participated in calcium-dependent intercellular interactions. Moreover, ectopic over-expression of ZN-cadherin, following mRNA microinjection into 2-4 cell embryos, caused microaggregation and uneven segregation of deep cells, resulting in distorted embryos. Developmental Northern and Western blot analyses indicated that both the mRNA and the protein first appear at gastrulation. In-situ hybridization showed that ZN-cadherin mRNA was initially present in all deep cells, and later became restricted to various epithelial and neural tissues. Whole-mount immunostaining indicated that while ZN-cadherin was already present at 50% epiboly, it became associated with cell junctions only 4-5 h later. In developing somites ZN-cadherin expression was prominent but transient. High levels of the protein were detected in epithelial somites and its expression was apparently down regulated concomitantly with the onset of myogenesis.