Cellular and molecular events in early and mid gestation porcine implantation sites: a review.

Commercial, North American pork breeds (Sus scrofa) experience significant loss of genetically-normal conceptuses during the peri-implantation (attachment) period and at mid-gestation (day 50 to 90 of the 114 day porcine gestation interval). Although exact causes for these losses are not defined, asynchronous in-utero development and deficits in vascularization of the endometrium and placenta appear to be involved. Understanding of normal maternal-fetal dialogue is critical to develop breeding or therapeutic strategies that improve fetal health and overall litter size in commercial pigs. The non-invasive, epitheliochorial porcine placenta permits investigation of maternal or fetal compartments without cross contaminating cells. We developed and use protocols to capture single, homogenous populations of porcine cells (endometrial lymphocytes, dendritic or endothelial cells) from histological sections using laser capture microdissection (LCM), a powerful tool for study of gene expression that reflects the in vivo environment. These data are compared with gene expression in biopsies of endometrium and of trophoblast from the same, attachment sites. Here we review justifications for selection of the genes we have studied and our published and in progress work. These data provide new insights into the roles of the endometrial immune environment in the regulation of the success and failure of porcine conceptuses.