The sheep genome harbours approximately 20 copies of endogenous beta-retroviruses(enJSRVs),and circumstantial evidence suggests that enJSRVs might play a role in mammalian reproduction,particularly placental morphogenesis.This study was aimed to assess the expression of mRNAs of an enJSRV and its receptor,HYAL2,in the uterus and conceptuses of Mongolian ewes throughout gestation,using real-time reverse transcription polymerase chain reaction and in situ hybridization analysis.The results showed that enJSRV and HYAL2 mRNAs were found to be expressed throughout gestation in the endometrium,chorion,placenta,and conceptus.The enJSRV mRNA was most abundant in the placenta on day 90 of pregnancy,in the endometrium on day 30 and 50,and in the chorion on day 70 and 110.However,HYAL2 mRNA was most abundant in the endometrium on day 30.These differences were all significantly different from each other(P<0.01).In situ hybridization showed that enJSRV and HYAL2 mRNAs were specifically expressed in endometrial luminal epithelium and glandular epithelium,trophoblastic giant binucleated cells(BNCs),endometrial caruncles,placental cotyledons,stroma,trophectoderm,as well as multinucleated syncytia of the placenta and blood vessel endothelial cells.Collectively,little is known about the molecular mechanisms by which trophoblastic differentiation and multinucleated syncytia formation are regulated by enJSRVs.However,the temporal and spatial distributions of enJSRV expression in the uterus and conceptus indicate that differentiation of BNCs and the formation of a multinucleated syncytiotrophoblast involve enJSRV and possibly its cellular receptor,HYAL2.Therefore,enJSRV and HYAL2 appear to play important roles in the female reproductive physiology in this breed of sheep.
Endogenous beta retroviruses (enJSRV) are highly homologous with Jaagsiekte sheep retrovirus (exJSRV),this exogenous retrovirus is the aetiological agent of ovine pulmonary adenocarcinoma (OPA). The aim of this study was to clarify the function of enJSRV and the immunological mechanisms of its corresponding antibody, that is undetectable in JSRV-infected ovine serum. The expression of enJSRV envelope protein and Hyal-2 mRNA in immune organs and lungs of ovine fetuses and lambs were analyzed by Real-Time reverse transcription PCR and In Situ Hybridization using specific probes. In Situ Hybridization results indicated that the enJSRV envelope protein and Hyal-2 mRNA were expressed in thymus, spleen, mesenteric lymph nodes and lungs at different times, while no positive signals were detected in the negative controls. On the other hand, results from Real-Time reverse transcription PCR analysis showed that in 130d fetuses and 3d newborn lambs the enJSRV mRNA levels were much higher in organs associated with the immune system than that in lungs, especially in the thymus and spleen, but levels of Hyal-2 mRNA expression was not significantly different in all collected tissue. These results provided evidence from an immunology point of view to understand why the circulating antibodies against exJSRV are undetectable in JSRV-infected ovine, and will help to unravel the pathogenesis of JSRV-infected ovine.
Endogenous retroviruses(ERVs) are a component of the vertebrate genome and originate from exogenous infections of retroviruses in the germline of the host. ERVs have coevolved with their hosts over millions of years. Envelope glycoproteins of endogenous retroviruses are often expressed in the mammalian placenta, and their potential function has aroused considerable research interest, including the manipulation of maternal physiology to benefit the fetus. In most mammalian species, trophoblast fusion in the placenta is an important event, involving the formation of a multinucleated syncytiotrophoblast layer to fulfill essential fetomaternal exchange functions. The key function in this process derives from the envelope genes of endogenous retroviruses, namely syncytins, which show fusogenic properties and placenta-specific expression. This review discusses the important role of the recognized endogenous retrovirus envelope glycoproteins in the mammalian placenta.
