Tissue interactions in basal regions of the cranial neuroepithelium in the C57BL mouse

Developmental interactions of neuroepithelial cells with mesenchymal cells and with notochordal cells were analyzed in the presumptive hindbrain of C57BL mouse embryos at stages 13 and 14 (8 and 9 days). Basal regions of the neuroepithelium and its basal lamina were also analyzed ultrastructurally by means of lanthanum tracer studies and with tannic acid treatment, and correlations were made with comparable features at the middle spinal cord level. At stage 13 the presumptive hindbrain showed less intercellular space in the basal one-third of the neuroepithelium than in its intermediate one-third, whereas at stage 14 the basal intercellular space increased to an amount roughly equal to that in the intermediate region. Lanthanum tracer penetrated readily from the basal aspect of the cells into the intercellular spaces. Microfilaments were observed in the basal cytoplasm immediately subjacent to the cell membrane. However, in contrast to apical regions, the microfilaments do not span or constrict the basal portion of the cytoplasm, suggesting a different functional role basally than apically. Projections from mesenchymal cells and from notochordal cells were in contact with the neural basal lamina. The notochordal cells, however, showed a closer relationship, including more processes and broader areas of contact, with strands of basal laminar material spanning the gap between notochord and neural tube.