Characterization of the expression of XPR1 in ovine utero-placental tissues

Phosphate is an essential regulator of conceptus development, but there is limited understanding of mechanisms regulating phosphate availability in utero-placental tissues. These experiments characterized the expression of xenotropic and polytropic retrovirus receptor 1 (XPR1), a phosphate exporter, in ovine utero-placental tissues. In Experiment 1, ewes were hysterectomized on day 1, 9, or 14 of the estrous cycle or day 30, 50, 70, 110, or 125 of pregnancy. Day of the estrous cycle did not affect XPR1 mRNA expression or protein localization. Expression of XPR1 mRNA decreased with day of gestation in placentomes, while XPR1 protein was detectable in uterine epithelia, blood vessels, endometrial stromal cells, myometrium, caruncular stroma, and syncytium of the placentome. In Experiment 2, ewes received daily injections of either corn oil vehicle (CO) or 25 mg progesterone (P4) in vehicle for the first 8 days of pregnancy and were hysterectomized on either day 9, 12, or 125. Endometrial stroma from P4-treated ewes had greater XPR1 immunoreactivity than CO-treated ewes on day 9. On day 125, endometria from P4-treated ewes had decreased expression of XPR1 mRNA compared to CO-treated ewes. Greater XPR1 protein immunoreactivity was present in uterine epithelia and stratum compactum stroma of P4-treated than CO-treated ewes. P4-treated ewes with a singleton fetus tended to have greater expression of XPR1 mRNA in placentomes than CO-treated ewes with a singleton fetus. Collectively, these results suggest a potential role of XPR1 in the regulation of phosphate availability in utero-placental tissues in ruminants.