Surface glycoproteins bearing alpha-GalNAc terminated chains accompany pyriform cell differentiation in lizards

The present investigation demonstrates that in squamate reptiles, as alread y reported for Podarcis sicula (Andreuccetti et al., 2001), the differentia tion of pyriform cells from small, stem follicle cells is characterized by the progressive appearance on the cell surface of glycoproteins bearing alp ha -GalNAc terminated O-linked side chains. Using a lectin panel (WGA, GSI- A4, GSI-B4, PSA UEA-I, PNA, Con-A, DBA, LCA, BPA, SBA), we demonstrated tha t, during previtellogenesis, the pattern of distribution of DBA binding sit es over the follicular epithelium dramatically changes. In fact, binding si tes first appear in follicular epithelium at the time that small cells begi n to differentiate; in such follicles, labeling is evident on the cell surf aces of small and intermediate cells. Later on, as the differentiation prog resses, the binding sites also become evident on the cell surface of pyrifo rm cells. Once differentiated, the pattern of the distribution of DBA bindi ng sites over the follicular epithelium does not change. By contrast, durin g the phase of intermediate and pyriform cell regression, DBA binding sites gradually decrease, so that the monolayered follicular epithelium of vitel logenic follicles, constituted only by small cells, shows no binding sites for DBA. It is noteworthy that binding sites for DBA are present on small c ells located in contact with the oocyte membrane, but not on those located under the basal lamina or among pyriform cells, and therefore not engaged i n the differentiation into pyriform cells. This finding demonstrates that, in squamates, the pattern of distribution of alpha -N-GalNAc containing gly coproteins significantly changes during previtellogenesis, and that these m odifications are probably related to the differentiation of small stem cell s into highly specialized pyriforms. J. Exp. Zool. 290:769-776, 2001. (C) 2 001 Wiley-Liss, Inc.