Structural and developmental relationship between capsular glycoproteins of the horse (Equus caballus) and the donkey (Equus asinus)

Abstract

Summary In the present study, we have investigated the molecular structure and biosynthesis during development of the donkey capsule, which replaces the zona pellucida and envelops the conceptus during the 2nd and 3rd weeks of gestation, before uterine attachment, and compared it with that of the horse. Amino acid analysis of capsules from accurately aged donkey conceptuses indicated that the polypeptide backbone of the constituent glycoproteins was very similar in both species. Carbohydrate analysis and lectin histochemical staining showed that, as in the horse, the major sugars present were sialic acid, N‐acetylgalactosamine and galactose. However, the donkey capsule contained substantially lower amounts of sialic acid. Removal of the covalently‐bound O‐linked carbohydrate by β‐elimination indicated that the donkey capsule resembles that of the horse in being O‐glycosylated mainly on threonine residues. The dry masses of donkey capsules remained low between Days 8.5 and 11.5, and increased rapidly with blastocyst expansion up to Day 17.5, as in the horse. However, the maximum capsular weight attained in the donkey (2.5 mg) was only half that of the horse and the decline in capsule weight up to Day 22.5, shortly before its disappearance, was steeper and occurred earlier. A monoclonal antibody (OC‐1), which reacts with a developmentally regulated epitope in the horse capsule, cross‐reacted strongly with both the capsule and trophoblast in frozen sections of donkey conceptuses. The differences in OC‐1‐reactive antigen expression in the donkey trophoblast mirrored those observed for the increase in capsular dry mass. The biochemical and developmental similarities observed between the capsule of the donkey and the horse suggest that this structure has been highly conserved in equids.

Markers of equine placental differentiation: insights from gene expression studies

“…Indeed, it is a commonly held view across species that the placenta expresses very few placental-specific genes as they would be a target for immunological attack by the mother's immune system. A anti-trophoblast antibody (102.1) that labels equine allantochorion and chorionic girdle trophoblast cells between day 12 and term has been widely utilized by researchers since the initial report (Oriol et al 1993). The antibody labels an unknown antigen, with the original study suggesting it may be trophoblast specific as the antibody failed to label other cells in day 8 embryos as well as all 18 adult and 6 non-placental fetal tissues assessed (Oriol et al 1993).…”

“…A anti-trophoblast antibody (102.1) that labels equine allantochorion and chorionic girdle trophoblast cells between day 12 and term has been widely utilized by researchers since the initial report (Oriol et al 1993). The antibody labels an unknown antigen, with the original study suggesting it may be trophoblast specific as the antibody failed to label other cells in day 8 embryos as well as all 18 adult and 6 non-placental fetal tissues assessed (Oriol et al 1993). There were two transcripts in our metanalysis that had an expression profile across placental and non-placental tissues that best matched this antigen distribution: Claudin 1 (CLDN1) and Iroquois-class homeodomain protein 4 (IRX4).…”

Nutrition of Broodmares

“…days post-ovulation 58 . At this time and for the next 20-25 days, the embryo is surrounded by a capsule composed of glycoproteins which regulates the assimilation of uterine secretions 4,59 .…”