Evidence of glycan mosaicism in the equine oviduct

We report a lectin histochemical study of oviductal ampulla and isthmus of thirteen mares euthanised at anestrus (1), estrus (5), 1-day post-ovulation (5) or diestrus (2). Staining with a panel of 5 lectins recognizing N-Acetylgalactosamine (GalNAc) residues revealed mosaicism in glycan expression in some specimens of ampulla and isthmus, peaking at estrus and 1-day post-ovulation (ov+1). In the ampulla, this presented as positively stained areas of both ciliated and non-ciliated cells in otherwise negatively-stained ampullae, ranging from small foci (diestrus) to areas up to 200 microns in length or more (estrus and ov+1). No positive clusters were observed in anestrus. In the isthmus, there was 1 specimen at estrus exhibiting discrete areas lacking stain with all five GalNAc-binding lectins which showed strong staining in the rest of the tissue, while at ov+1, another specimen showed unstained areas with 3 of the 5 GalNAc binding lectins. In both isthmus cases, terminal lactosamine (Gal-GlcNAc-) and α2-3-linked sialic acid were present in the unstained foci but were negligible elsewhere. Other glycans did not appear to be affected in this way. Various lectins and pre-treatment to cleave terminal sialic acid residues were used to assess how terminal glycosylation might differ between areas showing mosaicism and other epithelial cells in the respective tissue compartments. We suggest that one explanation for this mosaicism may be that it has resulted from absence or activation of a GalNAc transferase in clones of cells, most likely the blood group A-related enzyme UDP-GalNAc:Fuc α1-2 Gal α1-3GalNAc transferase. These glycosylation patterns may affect the adherence of sperm and/or zygotes to these sites, and more studies are required to evaluate the extent of its occurrence and functional significance.