Molecular mechanisms of embryonic implantation in mammals: Lessons from the gene manipulation of mice

BACKGROUND: Human infertility has become a serious and social issue all over the world, especially in developed countries. Numerous types of assisted reproductive technology have been developed and are widely used to treat infertility. However, pregnancy outcomes require further improvement. It is essential to understand the cross‐talk between the uterus (mother) and the embryo (fetus) in pregnancy, which is a very complicated event. METHODS: The mammalian uterus requires many physiological and morphological changes for pregnancy‐associated events, including implantation, decidualization, placentation, and parturition, to occur. Here is discussed recent advances in the knowledge of the molecular mechanisms underlying these reproductive events — in particular, embryonic implantation and decidualization — based on original and review articles. MAIN FINDINGS (RESULTS): In mice, embryonic implantation and decidualization are regulated by two steroid hormones: estrogen and progesterone. Along with these hormones, cytokines, cell‐cycle regulators, growth factors, and transcription factors have essential roles in implantation and decidualization in mice. CONCLUSION: Recent studies using the gene manipulation of mice have given considerable insight into the molecular mechanisms underlying embryonic implantation and decidualization. However, as most of the findings are based on mice, comparative research using different mammalian species will be useful for a better understanding of the species‐dependent differences that are associated with reproductive events, including embryonic implantation.