Alpha actinin distribution and extracellular matrix products during somitogenesis and neurulation in the chick embryo

A discrete stage in two different morphogenetic processes has been examined employing fluorescently labelled alpha‐actinin as a probe to localize native alpha‐actinin and antibodies to localize fibronectin and collagen type I. The stage of somitogenesis examined is the transition from the compact mesenchymal somitic mass to the epithelial somitic vesicle (ie, epithelialization of the somite). The stage of neurulation examined is the transition from the relatively flat neuroepithelium to the approximation of the neural folds. Before these morphogenetic movements begin, the neuroepithelium is sitting upon a basal lamina and interstitial collagen, and the somite is surrounded by a meshwork of interstitial collagen. During both of these processes, the cells become narrowed at their apices in the region of the tissue that is becoming concave, and alpha‐actinin is localized in the apices. The localization of intracellular alpha‐actinin and extracellular fibronectin, and the distribution of collagen, suggest that there is a coordinated appearance and distribution of these molecules that is temporally associated with these discrete morphogenetic events.