Physiology and Endocrinology Symposium: biological role of interferon tau in endometrial function and conceptus elongation.

This review integrates established and new information on the biological role of ovarian progesterone (P4) and interferon tau as well as conceptus- and endometrial-derived factors, PG and cortisol, in endometrial function and conceptus elongation during the periimplantation period of pregnancy in ruminants. Interferon tau is the maternal recognition of pregnancy signal that inhibits production of luteolytic pulses of PGF2α by the endometrium to maintain corpora lutea and their production of P4, the unequivocal hormone of pregnancy. Conceptus-endometrial interactions in ruminants are complex and involve carefully orchestrated temporal and spatial alterations in endometrial gene expression during pregnancy. Available results from studies in sheep support the idea that the individual, interactive, and coordinated actions of P4, interferon tau, PG, and cortisol regulate expression of elongation- and implantation-related genes in the endometrial epithelia and that P4 and PG are essential regulators of conceptus elongation. The outcome of these gene expression changes is alterations in endometrial secretions that govern conceptus elongation via effects on trophectoderm proliferation, migration, attachment, and adhesion. An increased knowledge of conceptus-endometrial interactions during early pregnancy in ruminants is necessary to understand and elucidate the causes of recurrent pregnancy loss and to provide a basis for new strategies to improve pregnancy outcome and reproductive efficiency.