Cell Constriction: Contractile Role of Microfilaments in Division and Development

The role of microfilaments in causing cell constrictions is discussed from a comparative point of view. Morphologically similar microfilaments occur in the contractile ring of dividing cells and in the apices of neural plate cells during neurulation. New evidence is presented regarding the distribution and orientation of apical microfilaments in neural plates of chicks and salamander embryos. These findings complement what is known about neurulation in frogs and cell cleavage in a variety of cells. In all cases, cell constriction occurs precisely and exclusively at those planes in which circular arrays of microfilaments are found. A sliding mechanism of microfilament contractility is discussed, as are possible mechanisms involved in filament alignment. Attention is given to the cell surface as a substratum for microfilament assembly. New evidence is presented regarding the early morphological determination of the neural plate in Xenopus , even before microfilaments are clearly evident or invagination begins.