Expression of interferon regulatory factors one and two in the ovine endometrium: effects of pregnancy and ovine interferon tau.
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Availble evidence suggests that interferon tau (IFNtau), the signal for pregnancy recognition in ruminants, suppresses transcription of the estrogen receptor (ER) gene in the endometrial lumenal epithelium (LE) and superficial glandular epithelium (sGE) to prevent oxytocin receptor (OTR) expression and pulsatile release of luteolytic prostaglandin F2alpha. The IFN regulatory factors one (IRF-1) and two (IRF-2) are transcription factors induced by type I IFNs that activate and silence gene expression, respectively. The objectives of these studies were to determine effects of pregnancy and IFNtau on expression of immunoreactive IRF-1 and IRF-2 proteins in the ovine endometrium. In study one, IRF-1 and IRF-2 were not detected in the LE or sGE of cyclic ewes. In pregnant ewes, IRF-1 expression was detected transiently in the LE and sGE only on Days 11 and 13, and IRF-2 was detected in these same epithelia on Days 13, 15, 17, and 20. In study two, 36 ewes were fitted with uterine catheters on Day 5 of the estrous cycle, and one uterine horn was double-ligated at the base. Uterine horns of each ewe received twice-daily injections of either recombinant ovine IFNtau or control proteins beginning on Day 11 until hysterectomy at 1, 3, 6, 12, 24, 48, 72, 96, or 120 h after initial injection. The IRF-1 was detected transiently in the endometrial LE and sGE only at 12 and 24 h in the uterine horn receiving IFNtau but not in those tissues receiving control proteins. The IRF-2 was expressed in the LE and sGE at 24 h and thereafter in the IFNtau-treated, but not control uterine horns. In control uterine horns, ER and OTR were first detected in the LE at 48 h and 72 h, respectively, and remained abundant thereafter. In horns receiving IFNtau, ER and OTR expression was not detected in the endometrial LE and sGE. Results suggest that IFNtau acts directly on the LE and sGE during pregnancy to sequentially induce IRF-1 and then IRF-2 gene expression, which is correlated temporally with an absence of ER and OTR. The ovine ER gene may contain an IFNtau-responsive element(s) that binds negative-acting, IFNtau-inducible transcription factors, such as IRF-2, which silences transcription of the ER gene in the endometrial epithelium during maternal recognition of pregnancy.
