Pre-implantation conceptus and maternal uterine communications: molecular events leading to successful implantation

Abstract

Implantation, a critical step for mammals in establishing pregnancy, requires successful completion of sequential events such as maternal uterine development, conceptus development and attachment, and placental formation. To reach the stage of placental formation, synchronized development of the conceptus and uterus throughout the implantation period is absolutely required. A number of factors expressed at the uterine endometrium and/or conceptus, which are associated with peri-implantation development, have been identified. In addition to a temporal and spatial expression of these factors, their roles in intra- and inter-cellular interactions make it difficult to fully understand physiological roles played during the critical period. This paper focuses on early conceptus development, maternal preparation for implantation and uterine-conceptus communication during the pre-implantation period, rather than the subsequent events such as conceptus attachment to the maternal endometrium. New aspects of pre-implantation processes are evaluated through simultaneous expressions of transcription factors as they possibly regulate the complex processes of implantation events in murine species and ruminant ungulates.