GLYCOCONJUGATE EXPRESSION IN THE CHICK EMBRYONIC CHORIOALLANTOIC MEMBRANE - COMPARISONS OF THE CHORIONIC ECTODERM AND ALLANTOIC ENDODERM

Background: The chorioallantoic membrane (CAM) of the chick embryo exp ands during embryogenesis to meet the increased oxygen demands during growth and differentiation. Temporal and spatial glycosylation pattern s of CAM ectodermal and endodermal proteins likely contribute to diffe rentiation of the functional attributes of the CAM. Methods: Using lec tins for light and electron microscopic observations, we studied the p atterns of glycoconjugate expression on the ectoderm and endoderm of t he chorioallantoic membrane (CAM) of the chick at days 4.5, 5.0, 5.5, 6.0, and 10 of morphogenesis. For Light microscopy, samples of unfixed CAM were incubated with the following FITC lectins: Con A, DBA, GSA-I , GSA-II, PNA, SEA, UEA-I, and WGA. Results: All lectins, except GSA-I and -II, gave positive results. The positive lectins, labeled with HR P, served to ultrastructurally localize PNA, SBA, and WGA, but nor, DB A binding to the luminal surface of the endoderm. UEA-I and Con A. bou nd similarly except on day 10 when UEA-I no longer bound. On the ectod ermal surface, only WGA bound at all times studied. PNA and SBA bindin g were present from days 5.0 to 6.0 but absent at days 4.5 and 10. DBA binding occurred through day 5.0 but was absent thereafter. UEA-I bou nd to the ectoderm at days 4.5, 5.0, and 10 but not days 5.5 and 6.0. Con A bound only on days 5.0 and 10. Conclusion: That the ultrastructu rally similar ectoderm and endoderm of the CAM display functional diff erences conforms to the hypothesis that differential expression of gly coconjugate microdomains likely contributes to such functional special ization. (C) 1995 Wiley-Liss, Inc.