Epithelial involution and basement membrane loss during early rhombencephalic tectoria lamina development

Extracellular material molecules play a key role in the regulation of morphogenesis and differentiation of a large number of organs including the central nervous system. However, the role of the neural basement membrane in the growth of different parts of the neural tube has yet to been delineated. Here, the structural and compositional modifications of the basement membrane (BM) of rhombencephalic tectoria lamina anlage (RTLA) have been examined during the process of RTLA epithelial attenuation. Between stages 10 to 11-the presumptive RTLA epithelium showed a structure, thickness and cell-proliferating capacity similar to those observed in other zones of the rhombencephalic walls. Moreover, the rhombencephalic vesicles were surrounded by a continuous BM that was heterogeneous both ultrastructurally and with regard to ruthenium red, laminin and tenascin distribution. After stage 11, the RTLA epithelium underwent a rapid process of attenuation and change to a stratified flattened epithelium. During this remodelling process, apoptosis and inhibition of both PCNA expression and 3H-thymidine uptake occurred in the RTLA epithelium. The BM of the RTLA underwent a process of degration at the beginning of the remodelling, and apoptosis and cell proliferation inhibition of RTLA epithelium were also observed. The loss of the biochemical signals encoded within the BM could lead to cell shape changes, cell proliferation inhibition and to the anoikis type of cell death. Our findings support the idea that the BM surrounding the neural tube plays a key role in controlling both the structure and growth of the CNS during the early developmental stages.