Probing Cadherin Interactions in Zebrafish with E- and N-Cadherin Missense Mutants

Abstract

Cadherins are cell adhesion molecules that regulate numerous adhesive interactions during embryonic development and adult life. Consistent with these functions, when their expression goes astray cells lose their normal adhesive properties resulting in defective morphogenesis, disease, and even metastatic cancer. In general, classical cadherins exert their effect by homophilic interactions via their five characteristic extracellular (EC) repeats. The EC1 repeat provides the mechanism for cadherins to dimerize with each other whereas the EC2 repeat may facilitate dimerization. Less is known about the other EC repeats. Here, we show that a zebrafish missense mutation in the EC5 repeat of N-cadherin is a dominant gain-of-function mutation and demonstrate that this mutation alters cell adhesion almost to the same degree as a zebrafish missense mutation in the EC1 repeat of N-cadherin. We also show that zebrafish E-and N-cadherin dominant gain-of-function missense mutations genetically interact. Perturbation of cell adhesion in embryos that are heterozygous mutant at both loci is similar to that observed in single homozygous mutants. Introducing an E-cadherin EC5 missense allele into the homozygous N-cadherin EC1 missense mutant more radically affects morphogenesis, causing synergistic phenotypes consistent with interdependent functions being disrupted. Our studies indicate that a functional EC5 repeat is critical for cadherin-mediated cell affinity, suggesting that its role may be more important than previously thought. These results also suggest the possibility that E-and N-cadherin have heterophilic interactions during early morphogenesis of the embryo; interactions that might help balance the variety of cell affinities needed during embryonic development.

An analysis of contractile and protrusive cell behaviours at the superficial surface of the zebrafish neural plate

“…Here we show the two tissues are in intimate contact, apparently without intervening extracellular matrix, and Cdh1 and Ctnna distributions suggest neural plate and EVL adhere to each other. Our antibody labelling suggest Cdh1 is expressed in membranes of both EVL and plate cells, so EVL/neural plate adhesions could be mediated by homophylic Cdh1 interactions, however since heterophylic interactions between Cdh1 and Cdh2 have been shown in mammalian cells (Straub et al, 2011; Labernadie et al, 2017) and suggested in zebrafish embryos (Warga and Kane, 2018) there may also be heterophylic adhesions between EVL and neural plate. None the less, EVL/neural plate adhesions must be either relatively weak or rapidly dynamic to enable the motile plate to move against the static EVL.…”

“…The protrusions from both layers lie sandwiched in the plane of the interface and do not protrude into the cells of the opposing layer. The distribution of Cdh1 suggests EVL and neural plate cells are likely to adhere to one another through homophylic adhesions and heterophilic Cdh1-Cdh2 adhesions across the tissue interface may also be possible (Ounkomol et al, 2010; Straub et al, 2011; Labernadie et al, 2017; Warga and Kane, 2018).…”