Cell surface proteins in the early embryogenesis of Pleurodeles waltlii

Surface proteins in the first embryonic stages (8-32 cells, morula, blastula, early and late gastrula) of Pleurodeles waltlii were selectively labelled by 125I using lactoperoxidase and glucose/glucose oxidase. Iodination was effected either on non-dissociated embryos or after their dissociation with EDTA. On the outer surface of non-dissociated embryos the two-dimensional electrophoresis revealed only three groups of 125I-labelled proteins which did not change during all studied stages. Quite different results were obtained with the cells of dissociated embryos. In addition to the iodinated proteins of the embryonic outer surface seven major iodinated proteins were identified. These proteins originate from the regions of cell-cell contacts in intact embryo. Their two-dimensional pattern in dissociated cells changes between stages 8-32 cells and morula. The next important difference was observed during gastrulation, which corresponds in Pleurodeles waltlii to the first morphogenetic movements. Therefore the outside and inside cell surfaces of embryo are different already at stage 8-32 cells (and probably earlier), before the first step of morphogenesis. The changes of cell surface proteins at early embryonal development take place inside the embryo, in the regions of cell-cell interactions.