Embryo–epithelium interactions during implantation at a glance

Abstract

At implantation, with the acquisition of a receptive phenotype in the uterine epithelium, an initial tenuous attachment of embryonic trophectoderm initiates reorganisation of epithelial polarity to enable stable embryo attachment and the differentiation of invasive trophoblasts. In this Cell Science at a Glance article, we describe cellular and molecular events during the epithelial phase of implantation in rodent, drawing on morphological studies both in vivo and in vitro, and genetic models. Evidence is emerging for a repertoire of transcription factors downstream of the master steroidal regulators estrogen and progesterone that coordinate alterations in epithelial polarity, delivery of signals to the stroma and epithelial cell death or displacement. We discuss what is known of the cell interactions that occur during implantation, before considering specific adhesion molecules. We compare the rodent data with our much more limited knowledge of the human system, where direct mechanistic evidence is hard to obtain. In the accompanying poster, we represent the embryo-epithelium interactions in humans and laboratory rodents, highlighting similarities and differences, as well as depict some of the key cell biological events that enable interstitial implantation to occur.

Adhesion molecules in gamete transport, fertilization, early embryonic development, and implantation—role in establishing a pregnancy in cattle: A review

“…This is followed by the reduced expression of E‐cadherin by epithelial cells and loosening of cell–cell adhesion within the epithelial layer. The latter allows the infiltration of the trophoblast and commencement of implantation (Aplin & Ruane, 2017; Coutifaris et al, 1991; Kokkinos et al, 2010). The second line of research in humans has proposed that the binding protein L‐selectin is expressed by trophoblasts and interacts with its ligand on uterine epithelia (Feng et al, 2017; Fukuda & Sugihara, 2008; Genbacev et al, 2003; Lai et al, 2005).…”

Direct Cell–Cell Interactions in the Endometrium and in Endometrial Pathophysiology

“…For successful implantation, however, gene expression in the endometrium in addition is regulated by the implanting blastocyst by precisely synchronized embryo-maternal interactions [60,61,62]. Both compartments of the endometrium are involved in this process: on the one hand, the epithelium has to allow adhesion of the embryo and invasion through the epithelium, on the other hand the stromal cells must be transformed to decidua cells which regulate trophoblast invasion and provide the placental blood supply necessary for embryo nutrition.…”

“…Degradation of the luminal epithelium and start of trophoblast invasion is observed from 5.5 dpc (mouse) or 6 dpc (rat) onwards [61,63]. Freeze fraction studies revealed that strands of tight junctions expand during the preimplantation phase of pregnancy on the lateral membrane of the uterine epithelial cells in pregnant rats [64] and in pseudopregnant rabbits [65].…”

Novel function of pregnancy-associated plasma protein A: promotes endometrium receptivity by up-regulating N-fucosylation

“…To establish successful embryo implantation, a normal developmental blastocyst and a receptive endometrium are required, as well as a synchronized conversation at the maternal-fetal interface 2 . During an extremely limited period, which is called the “window of implantation”, uterine endometrium undergoes morphological, biochemical and genetic changes to transform into a receptive status which can accept the blastocyst 3 .…”