Desmosomal cadherins in zebrafish epiboly and gastrulation

We find that zebrafish possess one Dsc, the orthologue of mammalian Dsc1, which we designate zfDsc. Unlike mammalian Dscs, zfDsc exists only as the "a" form since it lacks the alternatively-spliced mini-exon that shortens the cytoplasmic domain to produce the "b" form. Zebrafish possess two Dsgs, designated zfDsgα and zfDsgβ, orthologues of mammalian Dsg2. They show 43.8% amino acid identity and the α form has a 43 amino acid glycine-rich sequence of unknown function in its extracellular domain. Both zfDsc and zfDsgα were present as maternal and zygotic transcripts whereas zfDsgβ was first expressed from 8 hours post-fertilisation (hpf). All three transcripts were present throughout subsequent stages of development. Morpholino knockdown of both zfDsc and zfDsgα expression produced similar defects in epiboly, axis elongation and somite formation, associated with abnormal desmosomes or reduced desmosome numbers.These results demonstrate an important role for DCs and desmosomes in the early morphogenesis of the zebrafish embryo, provide a basis for more detailed analysis of their role and raise interesting questions relating to the evolution and functional significance of DC isoforms.Cell-cell adhesion is a key mechanism that guides and co-ordinates the dynamic rearrangements of cell populations during animal development. Early zebrafish development is characterised by many such cell movements including epiboly, the spreading of the blastoderm over the yolk, ingression or involution at gastrulation, and convergence and extension, which lengthen the embryonic axis during and following gastrulation. Cell adhesion mediated by the Type 1 cadherin E-cadherin has been shown to play an essential co-ordinating role in each of these processes [1-5] and N-cadherin regulates posterior body formation [6-8].Desmocollin (Dsc) and desmoglein (Dsg), the adhesion molecules of the intercellular junctions known as desmosomes, are also members of the cadherin superfamily [9-11]. Desmosome