PREGNANCY RECOGNITION IN RUMINANTS, PIGS AND HORSES - SIGNALS FROM THE TROPHOBLAST

Interferon tau (IFNtau) , secreted by trophectoderm of sheep, cow and goat conceptuses (embryo and associated membranes) , is the pregnancy recognition signal. The 172 AA mature IFNtau protein with conserved cy steine residues at positions 1, 29, 99 and 139 is a unique and largely uncharacterized subclass of Type I interferon. Interferon tau, the pa racrine antiluteolytic signal, acts on uterine epithelium to prevent p ulsatile release of PGF2alpha and insure maintenance of a functional c orpus luteum. Secretion of IFNtau is limited to early pregnancy, with Days 12-13 for sheep and Days 14-17 for cows and goats being critical for pregnancy recognition. Secretion of ovine (o) IFNtau is stimulated by granulocyte monocyte/macrophage colony stimulating factor (GM-CSF) or insulin-like growth factors I and II combined suggesting that uter ine factors influence IFNtau gene expression. There are few uterine re ceptors for oxytocin (OTR) or estrogen (ER) in early pregnant ewes or after intrauterine injections of oIFNtau, so pulsatile release of PGF required for luteolysis is abrogated. Ovine IFNtau may stabilize proge sterone receptors (PR) to inhibit up-regulation of ER and OTR in uteri ne epithelium to prevent luteolysis; an effect likely mediated by IFN- stimulated response elements in the receptor genomic DNA. Pig conceptu ses secrete both IFNalpha (25%) and IFNgamma (75%) between Days 15 and 21 of gestation, but their roles in early pregnancy are unknown. Inhi bition of secretion of luteolytic PGF in pigs is in response to estrog ens of blastocyst origin which induce upregulation of endometrial rece ptors for prolactin. Effects of prolactin and estrogen may be influenc ed by IFNalpha and/or IFNgamma from pig trophoblast. The equine concep tus may signal pregnancy recognition through secretion of a low molecu lar weight protein, estrogen and/or PGE, but the precise signal and it s mechanism of action have not been elucidated.