Functional analysis of autocrine and paracrine signalling at the uterine-conceptus interface in pigs.

The complexity of implantation necessitates intimate dialogue between conceptus and maternal cells, and precise coordination of maternal and conceptus signalling events. Maternal and conceptus-derived steroid hormones, growth factors and cytokines, as well as integrins and their ligands, have important and inter-related roles in mediating adhesion between apical aspects of conceptus trophectoderm and maternal uterine luminal epithelium that leads to formation of an epitheliochorial placenta. Integrin receptors appear to play fundamental roles in the implantation cascade and may interact with extracellular matrix molecules and other ligands to transduce cellular signals through autocrine and paracrine mechanisms. Functional in vitro analyses can be used to monitor individual contributions of specific integrin receptors and ligands to the signalling cascades of the maternal-conceptus interface. Integrative studies of implantation in pigs, using in vivo and in vitro approaches, are required to understand conceptus attachment and implantation in this species, and provide valuable opportunities to understand the fundamental mechanisms of implantation in all species.