CYTOSKELETON GRADIENTS IN 3 DIMENSIONS DURING NEURULATION IN THE RABBIT

Morphogenetic movements leading to the formation of the neural tube an d cellular differentiation leading to neuronal and glial cell lineages are both part of early development of the vertebrate nervous system. In order to analyze the degree of overlap between these processes, cel lular differentiation during the shaping of the neural plate is invest igated immunohistochemically by using monoclonal intermediate filament protein antibodies and the 7.5-8.0-day-old rabbit embryo as a model. Western blotting is used to confirm the specificity of the antibodies, which include a new monoclonal vimentin antibody suitable for double- labeling in combination with monoclonal cytokeratin (and fibronectin) antibodies. Starting in the early somite embryo and concomitant with n eural plate folding, a gradual loss of cytokeratin 8 (and 18) expressi on in the neuroepithelium is mirrored by a gain in vimentin expression with partial coexpression of both proteins. At the prospective rhombe ncephalic and spinocaudal levels, vimentin expression, in particular, changes (i.e., increases) along gradients in three dimensions: along t he longitudinal axis of each neuroepithelial cell from basal to apical , in the transverse plane of the embryo from dorsolateral to ventromed ial and along the craniocaudal axis from prospective rhombencephalic t oward spinocaudal levels of the neural plate. At the prospective mes- and prosencephalic levels, the expression change also proceeds from ba sal to apical within each neuroepithelial cell, but along the other ax es described here, the progress in expression change is more complex. Although the functional meaning of these highly ordered expression cha nges is at present unclear, the gradients suggest a novel pattern of n euroepithelial differentiation which may be functionally related to th e process of interkinetic nuclear migration (Sauer [1935] J. Comp. Neu rol. 62:377-402) and which partially coincides with the morphogenetic movements involved in the shaping of the neural plate. (C) 1995 Wiley- Liss, Inc.