The gastrulating chick blastoderm contains 16-kDa and 14-kDa galactose-binding lectins possibly associated with an apolipoportein

Extracts from chick blastoderms were subjected to affinity chromatography on lactoside-Sepharose. Lactose-eluted fractions were examined by gradient SDS-PAGE with silver staining, as well as by immunoblot analysis using antibodies to the chicken galactose-binding lectins of 14 kDa and 16 kDa and to an apolipoprotein of chicken very low density lipoprotein (Apo-VLDL-II). Fractions containing the highest lectin activity contained four main bands. One, unidentified, comigrated with albumin; two bands were identified by immunoblotting as the 14-kDa and 16-kDa lectins. The fourth band comigrated with Apo-VLDL-II and in immunoblot analysis reacted with antibodies to this apolipoprotein. In our electrophoretic system this protein migrates close to bovine trypsin inhibitor and has an apparent molecular weight of 6500 ± 500. The present studies establish the identity of this previously described 6.5 kDa protein (Zalik et al. J. Cell. Sci. 88, 483, 1987) as Apo-VLDL-II. While the 16-kDa lectin was present consistently in all the affinity-purified preparations, the relative frequencies of the 14-kDa lectin and Apo-VLDL-II varied. In sections of primitive streak blastoderms, lectin immunofluorescence was present in the lowest, most ventral area of the primitive groove and in the cells emerging laterally from the groove to form the endoderm. Cells of the extraembryonic endoderm also displayed high lectin immunoreactivity. The localization of the lectins is similar to the one described previously for Apo-VLDL-II. Double immunofluorescence staining indicates that Apo-VLDL-II and the lectin(s) colocalize. The copurification and colocalization of Apo-VLDL-II and the lectins in the chick blastoderm suggest that this apolipoprotein may associate with the galactose-binding lectins or may display lectin activity.