EXPRESSION OF THE GALACTOSE-BINDING LECTINS DURING THE FORMATION OF ORGAN PRIMORDIA IN THE CHICK-EMBRYO

Early chick embryos contain two R-galactoside-binding lectins of 16 kD a and 14 kDa. Using several antisera to these proteins, we have studie d lectin expression at embryonic stages when the segregation and early differentiation of organ primordia are taking place. With antisera to the 16 kDa lectin that display similar immunoreactivity in immunoblot analysis, we show that these antisera exhibit varying immunoreactivit y in embryo sections. One antiserum reacts preferentially with a matri x form of lectin while another detects mainly a cellular form of this protein. During early development, galactoside-binding lectins of the matrix type are expressed in the vitelline membrane, the outer and inn er limiting membranes of the neural tube, the surface of the notochord and the coelomic surf ace of the cardiac rudiments. The cellular form of the lectin occurs in the intracellular yolk of early embryos, in t he primordial germ cells, the myocardium, in the early myotome, and in a cohort of cells which are presumed to belong to the neural crest. O ur results indicate that, although all of the antisera recognize the i ntracellular lectin of the extraembryonic endoderm, some antisera to t he 16 kDa lectin exhibit preferential reactivity with different lectin isoforms. The extracellular matrix form of lectin is transiently expr essed during early development at the stages when the segregation of o rgan primordia is occurring. It's expression could be related to the a cquisition of polarity in developing epithelia. Results also suggest t hat various versions of the same protein may perform distinct developm ental roles in the embryo.