Receptor transporter protein 4 (RTP4) in endometrium, ovary, and peripheral blood leukocytes of pregnant and cyclic ewes.

Interferon-tau (IFNT) is secreted by the conceptus trophoblast and signals pregnancy recognition in ruminants. IFNT regulates expression of genes in the endometrium, peripheral blood leukocytes (PBLs), and corpus luteum (CL). Microarray analysis identified that expression of (chemosensory) receptor transporter protein 4 (RTP4) increased in PBLs during early pregnancy in cows. In the present study, we cloned and characterized RTP4 transcription during early pregnancy in ewes. Endometrium, PBLs, and CL were collected on Days 11, 13, and 15 of the cycle and on Days 11, 13, 15, 17, and 19 of pregnancy. Northern blot analysis revealed an expected 1.6-kb mRNA and an unexpected 2.6-kb mRNA. In endometria, RTP4 mRNA levels in cyclic ewes remained low, whereas RTP4 mRNA increased from Day 11 to Day 17 in pregnant ewes. Levels of RTP4 mRNA also increased from Day 15 to Day 19 in CL and PBL samples from pregnant ewes only. The RTP4 mRNA was located in the glandular epithelium, stratum compactum, and caruncular stroma. Ovine glandular epithelial cells were treated with IFNT to determine if IFNT alone could induce RTP4. IFNT increased RTP4 more than 70-fold at 1.5 h after treatment, with maximal induction of nearly 300-fold above values observed in nontreated controls at 6 h after treatment. These results indicate that RTP4 mRNA levels are induced in the ovine endometrium, PBLs, and CL by IFNT during early pregnancy and in cell culture in response to IFNT. If RTP4 expression affects G protein-coupled receptor function, it may be important for establishment of pregnancy in domestic ruminants.