Glycosylation at the fetomaternal interface in hemomonochorial placentae from five widely separated species of mammal: is there evidence for convergent evolution?

Hemomonochorial placentation occurs in diverse species. We have examined placental glycosylation in five widely separated mammals with this type of placentation – lesser hedgehog tenrec (Echinops telfairi), spotted hyena (Crocuta crocuta), nine-banded armadillo (Dasypus novemcinctus), human (Homo sapiens) and guinea pig (Cavia porcellus) – in order to assess whether evolutionary convergence to the hemomonochorial state is accompanied by a similar convergence of glycan expression. Placentae from 2 E. telfairi, 3 C. crocuta, 1 D. novemcinctus, 4 womenand 1 C. porcellus were fixed and processed into epoxy resin. Binding of twenty-three lectins was assessed using a semiquantitative ranking system. The trophoblast apical/microvillous membrane of all five species showed marked similarities in glycosylation. In the N-linked series, there were abundant bi/tri-antennary complex chains, while the non-bisected variants were much scarcer. All species had plentiful N-acetyl lactosamine sequences; at chain termini, binding to Galβ1,4GlcNAc and Galβ1,3GalNAc sequences was greatly enhanced after neuraminidase treatment. In all species, terminal NeuNAcα2,3 residues were detected. The tenrec had unusually abundant terminal N-acetyl galactosamine. The basal plasma membrane/basal lamina showed glycosylation patterns distinct from the microvillous membrane in each case, indicating chemical diversity of the two opposite faces of trophoblast. Similar classes of glycan at the hemochorial interface suggest conservation of function. The observed lectin binding patterns suggest broad similarities of glycosylation that may have arisen by convergent evolution.