Glycoconjugate expression in the chick embryonic chorioallantoic membrane: comparisons of the chorionic ectoderm and...

The chorioallantoic membrane (CAM) of the chick embryo expands during embryogenesis to meet the increased oxygen demands during growth and differentiation. Temporal and spatial glycosylation patterns of CAM ectodermal and endodermal proteins likely contribute to differentiation of the functional attributes of the CAM.

Using lectins for light and electron microscopic observations, we studied the patterns of glycoconjugate expression on the ectoderm and endoderm of the 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, SBA, UEA-I, and WGA.

All lectins, except GSA-I and -II, gave positive results. The positive lectins, labeled with HRP, served to ultrastructurally localize PNA, SBA, and WGA, but not DBA binding to the luminal surface of the endoderm. UEA-I and Con A bound similarly except on day 10 when UEA-I no longer bound. On the ectodermal surface, only WGA bound at all times studied. PNA and SBA binding 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 bound 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.

That the ultrastructurally similar ectoderm and endoderm of the CAM display functional differences conforms to the hypothesis that differential expression of glycoconjugate microdomains likely contributes to such functional specialization.