Involvement of a neutral glycolipid in differential cell adhesion in the Xenopus blastula

Many different molecular species mediate cell adhesion during embryonic development. These can have either protein or carbohydrate functional groups, which can act in either a homophilic or a heterophilic manner, and often in concert. We report here that a monoclonal antibody, M4B, raised against Xenopus blastomere membranes, inhibits the calcium-dependent adhesion of dissociated blastomeres. M4B maintains its inhibitory effect on adhesion when converted into univalent fragments, and specifically affects calcium-dependent adhesion. The antigen is regulated in both space and time during early development. It is found on cell surfaces throughout the egg to blastula stages, but is more concentrated on cells in the animal and marginal zones of the blastula. It is dramatically downregulated during gastrulation, and becomes largely restricted to gut epithelium by the larval stages. We show also that M4B function is spatially differentiated at the blastula stage, since it inhibits the aggregation of dissociated animal cells to a greater extent than vegetal cells. This membrane antigen may therefore play a role in the differential adhesion observed between different regions of the blastula, and which we presume to underlie the segregation of the primary germ layers during gastrulation. M4B recognizes a complex of plasma membrane glycolipids. Periodate treatment destroys the ability of these glycolipids to react with the antibody, indicating that the epitope resides in the carbohydrate moiety of the glycolipids. Chemical characterization shows that it is a neutral glycolipid, and that the major component is of the glycoglycerolipid, rather than the more common glycosphingolipid class. Blocking experiments with oligosaccharides of defined structure, and antibody crossreactivity show that the M4B antibody does not recognize several known embryonic carbohydrate antigens. These results demonstrate that M4B antibody recognizes a novel group of developmentally regulated glycolipids which function in calcium-dependent cell--cell adhesion in the Xenopus blastula.