The gastrulating chick blastoderm contains lectin activity specific for beta-D-galactoside groups. The galactose-binding lectin isolated by affinity chromatography on rho-aminophenyl-beta-D-lactoside separates into two bands when studied by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. One of these LII has a relative molecular mass of 70 (+/− 2) X 10(3) while the other LI is a polypeptide that migrates with the dye front in 10% gels. We have prepared an antiserum against this lectin preparation and have affinity-purified antibodies against LI. When embryos at stages 3–7 were examined by immunofluorescence using the affinity-purified antibodies, lectin was expressed in cells at the lowest portions of the primitive streak as well as in cells migrating laterally from this region to form the endoderm. Lectin was also expressed by the cells of the extra-embryonic endoderm and the primordial germ cells of the proximal area opaca. In transfers of gradient gels stained with affinity-purified antibodies against LI, this lectin had an approximate molecular weight of 6.5 X 10(3). Our results indicate that this lectin is expressed in areas that are undergoing cell spreading.

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