Abstract
A critical point in mammalian development is when the early embryo implants into its mother's uterus. This event has historically been difficult to study due to the fact that it occurs within the maternal tissue and therefore is hidden from view. In this review, we discuss how the mouse embryo is prepared for implantation and the molecular mechanisms involved in directing and coordinating this crucial event. Prior to implantation, the cells of the embryo are specified as precursors of future embryonic and extra-embryonic lineages. These preimplantation cell fate decisions rely on a combination of factors including cell polarity, position and cell–cell signalling and are influenced by the heterogeneity between early embryo cells. At the point of implantation, signalling events between the embryo and mother, and between the embryonic and extraembryonic compartments of the embryo itself, orchestrate a total reorganization of the embryo, coupled with a burst of cell proliferation. New developments in embryo culture and imaging techniques have recently revealed the growth and morphogenesis of the embryo at the time of implantation, leading to a new model for the blastocyst to egg cylinder transition. In this model, pluripotent cells that will give rise to the fetus self-organize into a polarized three-dimensional rosette-like structure that initiates egg cylinder formation.
Highlights
A critical point in mammalian development is when the early embryo implants into its mother’s uterus
This process results in the formation of a hollow ball of cells, the blastocyst, which is capable of implanting into the maternal uterine wall and comprises the necessary cell types to give rise to both embryonic and extraembryonic tissues in later development
This raises the question—if all cells are the same, how do they know what to do? The most obvious way in which cells can be different from each other is their position within the embryo, with outside cells developing into TE, surface inner cell mass (ICM) cells becoming primitive endoderm (PE) and deep ICM cells becoming pluripotent EPI
Summary
Which the implantation process can occur [80]. The process of implantation can be divided into three phases: apposition, attachment and penetration. The diameter of the uterine lumen becomes reduced to position the floating embryo close to the luminal epithelium (LE). The first contact between the embryo and the mother is mediated by interdigitation of TE and LE microvilli, but this is insufficient for stable attachment. An anti-adhesive glycoprotein layer of mucins covers the uterine surface and serves as a barrier against pathogens. At the time of uterine receptivity, this layer is removed under the control of maternal hormones and actively by the embryo [81,82]. (a) mesometrial blood vessels luminal epithelium anti-mesometrial blastocyst (E4.5) (b)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call