In the Spotlight

Abstract

Implantation of the embryo is a multistage process crucial to a successful pregnancy that can only occur during a small window of opportunity. During this time, the blastocyst needs to be able to bind and invade the uterine wall. The endometrium, on the other hand, needs to be receptive to the invasion of the trophoblast. It has been estimated that about 75% of all concepti are lost before or at the time of implantation, and inadequate uterine receptivity is believed to account for two-thirds of implantation failures. Endometrium receptivity is therefore a topic of interest to the reproductive endocrinologist community, especially in light of unsuccessful in vitro fertilization cycles following the transfer of good embryos. Research has, therefore, focused on better understanding the molecular mechanisms that play a role at the time of implantation, both from the embryo and the endometrium side. Reproductive Science has recently published several interesting articles on this field. 1,2 In the current issue of Reproductive Sciences, Chen et al 3 take a step further into determining the dynamic players involved in the complicated physiological process of implantation from the endometrium perspective. With the aid of real-time quantitative polymerase chain reaction (PCR) and next-generation sequencing, the authors characterized the profile of messenger RNA (mRNA) and microRNA (miRNA) expression in the endometrium during the prereceptivity, receptivity, and implantation phases. Their results demonstrated that the genes mostly expressed at the implantation site are involved in providing energy for embryo implantation, producing functional protein to support embryo development, and trophoblast invasion. Of importance, the authors also verified that the tight regulation between miRNAs and mRNAs plays a major role in the endometrium receptivity preparation and maintenance of early pregnancy. Hub miRNAs (mmu-miR-96 and mmu-miR200b), in particular, were identified as upstream regulators of Bcl-2, klf13, and PGR.The characterization of the basic pathways involved in implantation leads to a better understanding of the whole process, potentially opening the doors to the discovery of new ways of improving the utero receptivity. Interestingly, however, oftentimes the learning process is turned around, with empirical results also bringing new clues into play. That has been the case with endometrial injury, which has proved to provide benefits to embryo implantation as discussed previously in Reproductive Sciences. 4 The underlying mechanisms to this process have, however, never been completely understood.In this same issue of Reproductive Sciences, Liao and colleagues 5 take a look at this favorable effect on embryo implantation through the establishment of a mouse model. The authors randomly allocated mice to either a control group (normal mating or mating with previous abdominal opening alone) or to an endometrial injury procedure protocol, where the animals were subjected to scratches with a blunt syringe on the right uterine...