RESUMO
In the dog, oocyte maturation, fertilization, and early embryo development take place within the oviduct in the presence of increasing circulating progesterone (P4) levels. Expression of the oviduct-specific glycoprotein 1 (OVGP1), known in other species to be estrogen-dependent, was explored by real-time quantitative reverse-transcriptase PCR, Western blotting, and immunohistochemistry in oviducts from adult Beagle bitches during anestrus and at five specific time periods around ovulation: during pro-estrus before the luteinizing hormone (LH) peak (Pre-LH); after the LH peak and before ovulation (Pre-ov); and at Days 1, 4, and 7 after ovulation (n = 6 bitches per stage). Plasma estradiol-17ß (E2) and P4 were assayed at all stages. The expression of canine OVGP1 (cOVGP1) was undetectable during anestrus, increased significantly from Pre-LH to Day 1 in parallel with a decrease in plasma E2-to-P4 levels, remained high at Day 4, then decreased at Day 7 in parallel with an increase in plasma P4 levels. In contrast to other mammals, the expression of cOVGP1 was higher in the isthmus than in the ampulla at all stages. In order to explore the potential regulation of cOVGP1 expression by steroids, the 5'-flanking region of the corresponding gene was analyzed for the presence of estrogen- (ERE) and P4-response-element (PRE). An imperfect ERE and three half-ERE were found in this region, but no PREs. In conclusion, cOVGP1 is highly expressed at the time and site of oocyte maturation and fertilization, and is probably under E2 regulation. Further studies are needed to identify the potential roles of cOVGP1 in each process.