Developmental expression of glycocomponents in the chick chorioallantoic membrane

Widespread interest has focused on the research of the chorioallantoic membrane (CAM) and its functional contribution to gaseous exchange, calcium reabsorption, water and electrolyte transport during chick embryogenesis. Nevertheless, very little information is available on the glycoconjugate components of this extra-embryonic structure. In the present study, we investigated by lectin histochemistry, the glycosylation pattern expressed in the CAM epithelia during embryonic development. Occurrence of sialic acid-associated glycoproteins was detailed by either specific lectins, which discriminate alpha2,3 and alpha2,6 sialoderivatives, or sialidase digestion combined with appropriate lectins to identify the sialic acid acceptor sugars. Lectin affinities proved to depend greatly on differentiation of the CAM epithelia which showed highest expression of binding sites during the second half of incubation up to hatching. Differences emerged between the chorionic and the allantoic epithelium, regarding qualitative, quantitative and temporal expression of sugar moieties. A cell type-specific distribution of glycocomponents was found in the chorionic epithelium where lectin binding sites were specifically located in the villus cavity cells. In the allantoic epithelium, high and heterogeneous occurrence of sialoglycoconjugates as well as specific presence of fucose residues were evidenced mostly in the granule cells. We conclude from these findings that various glycoconjugates in the CAM could participate in different physiological functions characteristic of the chorionic and the allantoic epithelium.