Oviductal, endometrial and embryonic gene expression patterns as molecular clues for pregnancy establishment

In higher animals, the beginning of new life and transfer of genetic material to the next generation occurs in the oviduct when two distinct gametes cells unite resulting in the formation of a zygote. The zygote then undergoes serial developmental processes in the oviduct and enters into the uterus where it faces challenges and scrutiny from the endometrial ecosystem. Thus, embryos that are able to establish an appropriate embryo–maternal dialogue are capable of developing to term whereas the incompetent ones can perish any time during the gestation period. Although several lines of evidences indicated that pregnancy loss is a multi-factorial phenomenon, the biochemical composition of the embryo and maternal environment are the main players to determine pregnancy outcome. Indeed, expression patterns of the genes are the driving forces that induce biochemical composition changes in embryo, oviduct and uterine environment. Thus, examining the molecular signals that are associated with oviductal or endometrial receptivity and embryo implantation is essential for establishing strategies to improve pregnancy success. Therefore, this review focuses on the contribution of oviduct and its transcriptome profile on early stage embryo development and the impact of endometrium and its transcriptome changes on peri and post embryo implantation. In addition, this paper integrates established facts about hormonal and molecular signatures associated with endometrial receptivity. Finally, the blastocyst and pre-conception endometrial gene expression profiles have been discussed in relation to the pregnancy outcome to highlight the potentials of blastocyst and pre-transfer endometrial transcriptome profile approach for selecting appropriate recipient and developmentally competent embryo.