Mutations inhalf baked/E-cadherin block cell behaviors that are necessary for teleost epiboly

Abstract

Epiboly, the spreading of the blastoderm over the large yolk cell, is the first morphogenetic movement of the teleost embryo. Examining this movement as a paradigm of vertebrate morphogenesis, we have focused on the epiboly arrest mutant half baked (hab), which segregates as a recessive lethal, including alleles expressing zygotic-maternal dominant (ZMD) effects. Here we show that hab is a mutation in the zebrafish homolog of the adhesion protein E-cadherin. Whereas exclusively recessive alleles of hab produce truncated proteins, dominant alleles all contain transversions in highly conserved amino acids of the extracellular domains, suggesting these alleles produce dominant-negative effects. Antisense oligonucleotides that create specific splicing defects in the hab mRNA phenocopy the recessive phenotypes and, surprisingly, some of the ZMD phenotypes as well. In situ analyses show that during late epiboly hab is expressed in a radial gradient in the non axial epiblast, from high concentrations in the exterior layer of the epiblast to low concentrations in the interior layer of the epiblast. During epiboly, using an asymmetric variant of radial intercalation, epiblast cells from the interior layer sequentially move into the exterior layer and become restricted to that layer; there they participate in subtle cell shape changes that further expand the blastoderm. In hab mutants, when cells intercalate into the exterior layer, they tend to neither change cell shape nor become restricted, and many of these cells 'de-intercalate' and move back into the interior layer. Cell transplantation showed all these defects to be cell-autonomous. Hence, as for the expansion of the mammalian trophoblast at a similar developmental stage, hab/E-cadherin is necessary for the cell rearrangements that spread the teleost blastoderm over the yolk.

Cdc42 GTPase and Rac1 GTPase act downstream of p120 catenin and require GTP exchange during gastrulation of zebrafish mesoderm

“…This role may underlie their importance in early development, since presomitic mesoderm is surrounded by cadherins. Both zebrafish embryos deficient in E-cadherin (Cdh1, epithelial cadherin) by knockdown with morpholino RNAs (Babb and Marrs, 2004) and the homozygous half baked/Ecadherin mutant embryos (Kane et al, 2005) have mild to severe defects almost identical to those we observed with knockdown of p120 catenin d1 with the AUG start-site MOs (Supp. Fig.…”

Cadherin-based intercellular adhesions organize epithelial cell–matrix traction forces

“…In development, differential adhesion has been shown to play an important role in cell sorting (61)(62)(63), and the reorganization of intercellular forces in this context is entirely unexplored. Furthermore, in wound healing, we expect strong cell-ECM forces to be generated at a wound edge due to the local loss of intercellular adhesion.…”

The zebrafish bcl-2 homologue Nrz controls development during somitogenesis and gastrulation via apoptosis-dependent and -independent mechanisms

“…30,31 Moreover, the knockdown of E-cadherin strongly affects early development in the zebrafish. 32 However, the knockdown of nrz does not seem to affect the expression of E-cadherin in the zebrafish gastrula (results not shown), whereas paraxial protocadherin, another adhesion molecule having a role during gastrulation, 33 is upregulated upon nrz knockdown (see Supplemental data S3). Thus, although the underlying molecular mechanisms remain to be determined, this report supports the idea that, during development, cell movements and adhesion may be controlled by Bcl-2 family members, at least in part via snail-dependent pathways, independently of apoptosis.…”