Insights into Conceptus-Reproductive Tract Interactions in the Pig

Abstract

A better understanding of the mechanisms mediating conceptus-reproductive tract interactions in pigs has important implications for breeding herd productivity and for understanding the effects of selection for reproductive merit on patterns of prenatal loss and associated changes in the uniformity and growth potential of offspring. Nutrition and metabolic state have an important impact on embryonic and fetal development, and there is extensive evidence for both direct and indirect effects of nutrition on the reproductive tract of pigs. Changes in progesterone status can be a key mediator of indirect effects on early embryonic development. Using the cyclic, unilaterally ovariectomized gilt model, we have initially confirmed steroid-dependent changes in the secretion of oviduct proteins (POSP 1–3) as one possible component of this effect. The identification of other genes that are differentially expressed in the oviduct in the peri-implantation period is progressing, using the DD-RT-PCR approach. At the uterine level, the study of the pattern of expression of matrix metalloproteinases (MMP) and their regulators during the peri-implantation period has contributed to our understanding of the regulation of the noninvasive type placental development in pigs. A failure of the blastocyst to express MMP-9 may be a key factor and seems to be dependent on local inhibitory regulation within the uterus. The coexpression of MMP-2, tissue inhibitor of MMP-2, and MMP-14 may be linked to the morphological development of the extraembryonic tissues. Changes in plasminogen activator expression are consistent with an estrogen-modulated role in tissue remodeling during embryogenesis. Studies of the integrin family of adhesion molecules also revealed key mediators of the adhesion and attachment process that is fundamental to the development of the diffuse, epitheliochorial placenta of pigs. The lack of the αv subunits on the apical surface of the trophoblast, associated with uterine epithelial expression of both αvβ1 and αvβ3, suggests that attachment is directed from the maternal side. From the perspective of the trophoblast, the low expression of the αvβ1 subunit is consistent with noninvasive placentation. The temporal expression of other integrins is consistent with a role in the migation of both extraembryonic endoderm and mesoderm during embryogenesis.