Time of appearance and tissue distribution of a cell surface antigen in early chick development.

The distribution of the antigen defined by monoclonal antibody 224-1A6-A1 in the early chick embryo was studied. The antigen is unequivocally present in the rudimentary neural tube as early as the 12 somite stage (approximately 40 h of incubation). The antigen appears on some but not all derivatives of the ectoderm and mesoderm, but appears to be absent on endodermal derivatives. Monoclonal antibody 224-1A6-A1 therefore serves as a marker for early events in the developmental sequence leading toward the formation of the nervous system.