Conceptus-derived interferon-tau (IFN-tau) has been implicated in the process of maternal recognition of pregnancy in the bovine. This type I IFN interacts with a uterine receptor complex to elicit secondary maternal responses, one of which is secretion of uterine proteins. We investigated the effects of pregnancy and recombinant (r) bovine (bo) IFN-tau (10(7) antiviral units/mg) on secreted proteins by cultured bovine endometrial explants. Explants were cultured for 24 h with [3H]leucine and dialyzed medium analyzed by one- and two-dimensional SDS polyacrylamide gel electrophoresis (PAGE) and fluorography. In one-dimensional PAGE experiments, endometrium representing early pregnancy (days 16-21) and the estrous cycle (days 16-19) was cultured in the presence of 5 nM rboIFN-tau and showed an increase (two- to five-fold) in secretion of 12- and 28-kD proteins. Further examination of these proteins by using two-dimensional PAGE indicated that the 12-kD protein was basic (pI > or = 7.5), whereas the 28-kD protein was acidic (pI approximately 5.0). Isoelectric focusing in the acidic range revealed that the 28-kD protein was composed of several isoelectric variants (pI 4.5-5.5). Although the functions of these secretory proteins are currently unknown, they serve as useful markers for IFN action and may act as secondary signals to protect the early developing conceptus.
We studied the biosynthesis of two proteins, p70 (Mr 70,000; pI 4.0) and p15 (Mr 15,000; pI 5.7), by endometrial tissues from ewes between Days 12 and 24 of pregnancy and between Days 12 and 16 of the oestrous cycle to determine whether production of the two was correlated with the period of biosynthesis of ovine trophoblast protein-1 (oTP-1) by the conceptus. We also compared the protein synthetic activities of endometrium from gravid and non-gravid horns of pregnant ewes at Days 14, 16 and 18 in which the conceptus had been confined to one uterine horn. Proteins p70 and p15 were produced maximally between Days 14 and 20 of pregnancy, but synthesis by endometrial cultures from cyclic ewes was low or absent. Furthermore, synthesis of Protein p70 in particular was much greater by the gravid than non-gravid horn of unilaterally pregnant ewes. We conclude that synthesis of Proteins p70 and p15 by the uterus of sheep coincides with the time of oTP-1 production by the conceptus.
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