Intermembrane distances at the feto-maternal interface in epitheliochorial placentation

Karl Klisch,Elisabeth M Schraner

doi:10.1016/j.placenta.2021.04.011

Abstract

IntroductionIn an epitheliochorial placenta, the apical membranes of trophoblast cells and of uterine epithelial cells are in contact to each other (feto-maternal contact). In addition, there are also folds in which the trophoblast membrane is in contact with itself (feto-fetal contact) and areas where apical uterine epithelial membrane is in contact with itself (materno-maternal contact). MethodsWe use transmission electron microscopy of placental samples from pigs.(n = 3), cows (n = 2), sheep (n = 2), goat (n = 2) and roe deer (n = 1) to study the intermembrane distance in these three contact types. ResultsThe measured intermembrane distances vary between 8 and 25 nm. One common feature is that the distance at feto-fetal contact sites is about 6–10 nm wider than at materno-maternal sites and feto-maternal sites show intermediate values. DiscussionThis finding suggests that the membrane distance at feto-maternal contact sites is determined by heterophilic binding of larger fetal to smaller maternal binding molecules. Homophilic binding of smaller maternal or larger fetal molecules lead to the smaller or wider intermembrane distances at materno-maternal or feto-fetal contact sites respectively. The observation that this similar pattern of membrane distances is present in pigs and in ruminants suggest that an evolutionary mechanism is involved in determining the intermembrane distance in epitheliochorial placentas.

Highlights

Intermembrane distances at the feto-maternal interface in epitheliochorial placentation
In an epitheliochorial placenta, the apical membranes of trophoblast cells and of uterine epithelial cells are in contact to each other
This finding suggests that the membrane distance at feto-maternal contact sites is determined by heterophilic binding of larger fetal to smaller maternal binding molecules

Summary

Introduction

The apical membranes of trophoblast cells and of uterine epithelial cells are in contact to each other (feto-maternal contact). Discussion: This finding suggests that the membrane distance at feto-maternal contact sites is determined by heterophilic binding of larger fetal to smaller maternal binding molecules. Homophilic binding of smaller maternal or larger fetal molecules lead to the smaller or wider intermembrane distances at materno-maternal or feto-fetal contact sites respectively. The observation that this similar pattern of membrane distances is present in pigs and in ruminants suggest that an evolutionary mechanism is involved in determining the intermembrane distance in epitheliochorial placentas. During the development of the epitheliochorial placenta, the connection between the trophoblast and the uterine epithelium passes through stages of apposition, adhesion and further into the formation of the definitive placenta, which is typically characterised by membrane attachment between interdigitating fetal and maternal microvilli [1,4]. Roles for adhesion molecules from different groups (e.g. integrins, cadherins) have been identified for these early stages, but the molecular basis of the attachment in later stages is much less well defined

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Results

Conclusion