Requirement of the juxtamembrane domain of the cadherin cytoplasmic tail for morphogenetic cell rearrangement during myotome development

During development, the activity of cadherin cell adhesion molecules is assumed to be regulated to allow for cell rearrangement or translocation. Previous studies suggest that the juxtamembrane (JM) domain of the cadherin cytoplasmic tail, which contains the site for binding to p120^ctn, has a regulatory function in this adhesion system. To study the possible role of JM domain–dependent cadherin regulation in embryonic cell rearrangement, we ectopically expressed a series of N-cadherin mutants in developing somites of chicken embryos. When a JM domain–deficient N-cadherin was expressed, the morphogenetic expansion of the myotome was strongly suppressed. However, a triple alanine substitution in the JM domain, which specifically inhibited the p120^ctn binding, had no effect on myotome development. Furthermore, a dominant negative N-cadherin, which had a deletion at the extracellular domain but maintained the normal cytoplasmic tail, did not affect myotome expansion; although it disrupted intersomite boundaries. Overexpression of p120^ctn also did not affect myotome expansion, but it did perturb myofiber orientation. These and other observations suggest that the JM domain of N-cadherin has a regulatory role in myotome cell rearrangement in which molecules other than p120^ctn are involved. The p120^ctn molecule itself seems to play a critical role in the arrangement of myofibers.