Membrane changes in neural target cells studied with fluorescent lectin probes.

The competent ectoderm of Pleurodeles waltl comprises two cell layers with characteristic differences in their morphology, their composition and the molecular arrangement of the various constituents. The use of labelled lectin probes for observations of ectoderm tissue in vitro with u.v. microscopy (epi-illumination) and the quantification of the results show the following: Differences in labelling according to the nature of the lectins (SBA, PSA, LCA and Con A). These differences provide information on the nature of the carbohydrates which are present at this stage and on the number of receptors. Differences in fluorescence intensity of the surfaces studied. The internal surface of the ectoderm is labelled more densely than the external surface. Rearrangement of the lectin receptors with a new molecular configuration, stressing the fluidity of the membrane (by the mobility of the receptors throughout the membrane) and its importance for the occurrence of neural induction. Existence of membrane glycoconjugate turnover. A difference in behavioural characteristics between the internal and the external surfaces with respect to the lectins and the formation of an extracellular matrix on the internal surface alone. The extracellular matrix seems to have a role in morphogenetic movements.