Human trophoblast function during the implantation process
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BioMed Central
Open Access
Review
Human trophoblast function during the implantation process Elsebeth Staun-Ram1,2 and Eliezer Shalev*1,2 Address: 1Laboratory for Research in Reproductive Sciences, Department of Obstetrics and Gynecology, Ha'Emek Medical Center, 18101, Afula, Israel and 2Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel Email: Elsebeth Staun-Ram - [email protected]; Eliezer Shalev* - [email protected] * Corresponding author
Published: 20 October 2005 Reproductive Biology and Endocrinology 2005, 3:56
doi:10.1186/1477-7827-3-56
Received: 01 August 2005 Accepted: 20 October 2005
This article is available from: http://www.rbej.com/content/3/1/56 © 2005 Staun-Ram and Shalev; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract The implantation process involves complex and synchronized molecular and cellular events between the uterus and the implanting embryo. These events are regulated by paracrine and autocrine factors. Trophoblast invasion and migration through the uterine wall is mediated by molecular and cellular interactions, controlled by the trophoblast and the maternal microenvironment. This review is focused on the molecular constituents of the human trophoblast, their actions and interactions, including interrelations with the uterine endometrium.
1. Introduction Successful implantation depends on synchronization between the developmental stages of the embryo itself and the complex series of molecular and cellular events that are induced in the pregnant uterus by paracrine and autocrine regulators [1]. Embryos prepare for implantation during their cleavage stage. Successive cleavages must produce sufficient cells by the time the blastocyst is formed to permit the full formation of inner cell mass and trophectodermal cells. The latter are the origin of the cytotrophoblastic cells which ensue to become either the villous cytotrophoblastic cells which will proliferate and differentiate by fusion to form the syncytiotrophoblast, or they will stream out of the syncytiotrophoblast to form mononuclear multilayered invasive extravillous cytotrophoblastic cells [2]. The process of implantation begins six to seven days following fertilization [3] and consists basically of three stages [4]. Apposition is the first stage denoting the initial, still unstable, adhesion of the blastocyst to the uterine wall. At this stage the pinopodes, which are micro protrusions from the apical uterine epithelium surface, inter-digitate with microvilli on the apical syncytiotrophoblast surface of the blastocyst[5] (Figure 1). The
stable adhesion, which is the next step, reveals an increased physical contact between the blastocyst and the uterine epithelium, while the embryonic pole is oriented toward the epi
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