A potential role for spectrin during neurulation.

An actin-myosin complex located in apical regions of the neurectoderm has been postulated to play a role in neurulation. Numerous studies have documented the presence of microfilaments in this area and confirmed their composition as actin. By necessity, if such a contractile system is to exert a force, these filaments must be anchored in some way to the cell membrane. In this study, the presence of the actin-binding protein, spectrin (fodrin), is demonstrated in the neurectoderm of neurulating mouse embryos using antispectrin antibodies and indirect immunofluorescent techniques. The patterns of spectrin localization correlate with the previously reported regions of increased numbers of microfilaments and also with the morphology of the neural folds. Thus, during the initial stages of cranial fold elevation, a process reportedly dependent on increased glycosaminoglycan synthesis, little spectrin is present in the neuroepithelial cells. Later as the folds begin to converge toward the midline, deposition of the protein, as demonstrated by the intensity of fluorescence, is increased in the apices of these cells, and is most prominent in regions of greatest bending in the neural folds. Caudal neural fold regions show a similar pattern of staining. Thus, the hypothesis that a cytoskeletal system assists in neurulation is supported by these results, which for the first time demonstrate the presence of a putative actin-membrane attachment protein in a morphogenetically active system.