EFFECTS OF THE ESTROUS-CYCLE AND EARLY-PREGNANCY ON UTERINE EXPRESSION OF MX PROTEIN IN SHEEP (OVIS-ARIES)

Conceptuses of ruminant ungulates produce large amounts of a type I in terferon, interferon-tau (IFN tau), which is the signal for maternal r ecognition of pregnancy. Induction of cellular Mx proteins is an impor tant component of the response to type I interferon in the immune syst em, but Mx regulation and function have not been studied in the uterus , This study examined temporal and spatial alterations in ovine uterin e Mx expression during the cycle and early pregnancy using immunohisto chemistry, in situ hybridization, and Northern and slot-blot analysis. Sheep uterine endometrium expressed a single similar to 2.5-kilobase Mx mRNA transcript that was detectable at all stages of the estrous cy cle and early pregnancy examined. In cyclic ewes, mRNA abundance in en dometrium increased from Day 1 to peak levels at Day 13 and then decli ned to Day 15. In pregnant ewes, steady-state levels of Mx mRNA were f irst detected above the level in cyclic ewes at Day 13 poetmating, wer e greater than 10-fold higher at Day 15, and remained elevated at Day 19. Expression of Mx mRNA in the myometrium did not change during the estrous cycle but increased similar to 23-fold between Days 11 and 15 of pregnancy. Immunohistochemical and in situ hybridization analysis r evealed a similar temporal pattern of Mx expression. In cyclic ewes, M x protein and mRNA were initially localized to the luminal epithelium at Days 1 and 3, increased from Days 5 to 13, especially in the shallo w uterine glands, and then declined at Day 15. pregnancy resulted in u p-regulation of Mx expression in the luminal and glandular epithelium, stroma, and myometrium. Punctate Mx immunostaining and Mx mRNA concen trations were greatest when progesterone production was maximal during the estrous cycle and were strongly upregulated by the conceptus acro ss the entire uterine wall. It is suggested that a cascade of inductio n of Mx gene expression proceeds from the luminal epithelium to the ou ter longitudinal myometrium and that transcriptional activation of the promoter may involve both soluble cytokines (i.e., IFN tau) and stero id hormones (i.e., progesterone).