Studies on the mechanism of neurulation in the chick: Microfilament‐mediated changes in cell shape during uplifting of neural folds

The organization and properties of microfilaments of developing chick neuroepithelial cells were investigated in an attempt to elucidate the structural basis for the observed changes in cell shape during uplifting of neural folds. Microfilaments in the apical regions of cells are more organized than those along the lateral and basal cell margins and are associated with developing junctions. At the level of the zonula occludens, microfilaments are arranged into a loose meshwork extending just below the luminal surface. At the level of the zonula adherens, microfilaments are organized into several discrete bundles rather than as a single circumferential bundle. The opposite ends of these bundles appear to make contact with the plasma membrane at specialized areas of the junction. Microfilaments in the peripheral cytoplasm of the neck and basal regions form a continuous but sparse meshwork. All of these microfilaments bind heavy meromyosin. The implications of the present findings to the observed changes in cell shape during uplifting of neural folds in the chick is discussed.