Embryo implantation: A time for recalling and forwarding

Abstract

The success of embryo implantation is a critical step towards further embryo development and pregnancy outcome. The observations and investigations on embryo implantation have been over a century. A huge body of knowledge has been accumulated in anatomy, histology, ultrastructure and hormonal regulation; as well as recently in depth information about molecular signaling pathways got from studies of genomic wide gene screening and specific gene deletion. The knowledge from basic research has also substantially helped to initiate and improve the Artificial Reproductive Technology (ART) in clinical applications. Now we've known that the normal embryo implantation involves the embryo's development into an implantation-competent blastocyst and the synchronized transformation of uteri into a receptive stage. The interdependent relationship between the blastocyst and uterus involves complicated hormonal regulation and local paracrine, juxtacrine interactions. In this paper, we review some important historical findings regarding uterine receptivity and blastocyst activation, as well as some less discussed topics such as embryo spacing, embryo orientation. Further understandings on detailed mechanisms during the process of embryo implantation will help cure women infertility as well as develop new generation of non-steroids contraceptives. embryo implantation, uterine receptivity, blastocyst activation, research history Pregnancy loss is a common pathological condition in human pregnancy, which is often seeded from early pregnancy around embryo implantation. The infertility issue is now drawing increasing public attention due to its worldwide social and economic impact. While the world is facing increasing population, there are still about 15% couples who could not have their children because of infertility. During the past decades, the development and clinical application of in vitro fertilization and embryo transfer (IVF-ET) have conquered many infertility problems and made new hopes for thousands of infertile couples. However, the implantation rate after embryo transfer is still disappointingly low (~30%), most possibly because the transferred embryo is not synchronized with the development of uterus (or the uterus is in the nonreceptive stage) [1] . Recently, evidence from both animal models and clinical survey supports a novel concept that the success of embryo im-plantation could no longer be simply judged by "implantation or not implantation". It is now recognized that the timing of implantation is also crucial to the ongoing embryo development and final pregnancy outcome. A short delay of implantation beyond the normal implantation window would result in subsequently increased pregnancy loss [2][3][4][5] . It is the quality of embryo implantation that determines the quality of ongoing pregnancy and fetal development. In this regard, in depth researches about detailed molecular mechanisms during embryo implantation are necessary to help us conquer two worldwide problems, infertility and development of novel contrac...

Oxidative stress and DNA damage in utero and embryo implantation of mice exposed to carbon disulfide at peri-implantation

“…18 If the condition of maternal uterus was disturbed, the loss of embryos would happen. 19 In our previous studies, CS 2 exposure at peri-implantation disturbed expression of MMP(metalloproteinase)-2, MMP-9, 20 leukemia inhibitory factor, 21 adhesion molecule fibronectin and its ligand, and integrin β1 in the uterus of gestational mice, 22 all these are related to implantation failure. Therefore, we speculated that CS 2 exposure might affect the environment of the uterus and disturb the development of the implantation window to disturb the process of embryo implantation.…”

The Effective Mechanism of Heat Stress on Mouse Embryo Implantation

“…Estrogen and progesterone regulate the expression of VGEF and their receptor on embryo preimplantation in various ways, and then uterine vascular permeability and angiogenesis were influenced. Progesterone participated in positive regulation of expression of HOXa-10 in uterine stroma [8,14].…”

Periostin and implantation: a new biomarker of embryo-endometrial cross talk

“…AKT, Wnt, SOX), regulates not only the embryogenesis but also the subsequent embryo migration, adhesion and development (20,21). Previous studies have suggested that embryos, via EMT activation, may influence endometrial receptivity too (22)(23)(24). In particular, it has been shown that human blastocyst before to implant releases, in vitro, soluble factors that differentially modify human endometrial epithelial cell adhesion and EMT gene expression (15,25).…”