Cadherins are a large family of cell-cell adhesion receptors, but despite intense research into their functions, many aspects of their activity remain somewhat elusive. Two papers in this issue of Development now shed new light on the significance of both cell-type specific cadherin expression and their subcellular localisation for their roles in development.
In the first study (), Christopher Wylie and co-workers report that, in Xenopus ectoderm, distinct morphogenetic movements result from actin assembly mediated by differential cadherin expression. The authors show that the Type I sub-family members C-, E- and N-cadherin all assemble cortical actin. They then analysed the localisation of these three cadherins in the developing ectoderm, which separates into two parts (neural and non-neural). The cadherins, they find, are temporally and spatially differentially expressed in the neural and non-neural ectoderm; where expression domains overlap, the cadherins are predominantly found in different subcellular locations. In addition, whereas N-cadherin depletion affects actin assembly in, and the morphogenetic movements of, neural ectoderm, E-cadherin depletion has similar effects in the non-neural ectoderm. The two cadherins, however,cannot replace each other in rescue experiments. Thus, the researchers propose, cadherins are important for actin assembly during morphogenesis, and their differential expression is crucial for generating distinct morphogenetic movements.
In the second study, Mahendra Sonawane, Christiane Nüsslein-Volhard and colleagues investigate cellular junction assembly in zebrafish and report that E-cadherin is involved in regulating this process(). The authors find that during the formation of hemidesmosomes, a type of cell junction that links the basal domain of epithelial cells to the extracellular matrix,E-cadherin and the polarity regulator Lgl2 localise to the lateral domain of epithelial cells. By contrast, the hemidesmosome component Integrin alpha 6(Itga6) localises to both the lateral and the basal domain. The authors then demonstrate that Lgl2 promotes the targeting of Itga6 to the basal membrane during hemidesmosome formation, whereas E-cadherin negatively regulates this process. Thus, two proteins localised to the lateral domain act antagonistically to regulate basal hemidesmosome formation. Together, these two studies highlight the context-dependent nature of cadherin interactions and indicate that their function might be influenced by their subcellular localisation.
