Polarized distribution of vinculin epitopes in Xenopus laevis embryos

Vinculin is a 130 kDa cytoskeletal protein which plays a central role in stabilizing the association between actin microfilaments and membrane adhesion receptors. We made use of two anti-vinculin monoclonal antibodies to study the distribution of different epitopes of this molecule during early development of Xenopus laevis. In a previous study we found that one of these antibodies recognized an isoform of vinculin characterized by a specific state of phosphorylation. We show here, that although vinculin protein is uniformly distributed throughout the embryo, this specific isoform of vinculin is only present in the animal pole of the cleavage stage embryo. This asymmetry persists in the blastula where only the blastocoel roof and cells of the marginal zone are stained by the antibody. During gastrulation and neurulation the invaginating mesoderm and neuro-ectoderm are the only positive structures, while the endoderm is negative. During later development the staining gradually disappears from the nervous system and from skeletal muscles to persist only in cardiac and smooth muscles. The asymmetric distribution of isoforms of a structural protein, important in the control of cell adhesion and motility, during the establishment of the axial polarities of the embryo, may play a crucial role in the control of early morphogenetic events.