Uterine glands: biological roles in conceptus implantation, uterine receptivity and decidualization

All mammalian uteri contain glands in the endometrium that synthesize or transport and secrete substances essential for survival and development of the conceptus (embryo/fetus and associated extraembryonic membranes). This review summarizes information related to the biological roles of uterine glands and their secretions in uterine receptivity, blastocyst/conceptus survival and implantation, and stromal cell decidualization. Studies with the ovine uterine gland knockout (UGKO) model support a primary role for uterine glands and, by inference, their secretions present in uterine luminal fluid histrotroph for conceptus survival and development. In rodents, studies with mutant and progesterone-induced UGKO mice found that uterine glands and their secretions are unequivocally required for establishment of uterine receptivity and blastocyst implantation and also may influence blastocyst trophectoderm activation and stromal cell decidualization in the uterus. Similarly in humans, histotroph from uterine glands appears critical for blastocyst implantation, uterine receptivity, and conceptus nutrition during the first trimester and uterine glands likely have a role in stromal cell decidualization. An increased understanding of uterine gland biology is important for diagnosis, prevention and treatment of fertility problems, particularly infertility and recurrent pregnancy loss, in domestic animals and humans.