The ontogenesis of cranial neuromeres in the rat embryo. II. A transmission electron microscope study.

The morphogenesis of rhombomeres (neuromeres) caudal to the preotic sulcus during neurulation in rat embryos is described. A model is proposed to explain the development of the characteristic neuromeric sulci and interneuromeric gyri based on the cytoskeletal elements and the kinetic behaviour of the neural epithelium. Evidence obtained from a study of control, cytochalasin D-treated and colchicine-treated embryos, at the electron microscopic level, supports the proposed model. The longitudinally expanding cranial neural epithelium bulges between microtubule blocks present within the interneuromeric gyri, causing a bulge to develop along the line of least resistance, away from the microfilament-rich luminal border of the neuromeric sulcus region.