| The genome of all mammals is colonized by ERVs derived from retroviruses that have invaded the host during evolution, which has led to persistent integration into the host DNA. Repeated retroviral integrations have occurred over many millions of years. The function of ERVs is not clear, but some of them might have biological functions in embryos implantation, cell fusion and placental morphogenesis. Endogenous betaretroviruses (enJSRVs) are present in the genome of sheep and highly related to exogenous jaagsiekte sheep retroviruses (exJSRVs); their exact biological roles are still being researched. Recent studies suggest that enJSRV high expression in gential tract epithelial cells is beneficial to the host. But exJSRV is the originated agent of sheep pulmonary adenocarcinoma (OPA), a contagious neoplastic lung cancer. And the cellular receptor for both exJSRV and enJSRV is hyaluronidase 2 (HYAL2). Little is known about the molecular mechanisms that trophoblast differentiation and multinucleated syncytia formation regulated by enJSRV.In order to study whether enJSRV and its receptor HYAL2 expressed in the uterus and embryos of the Mongolian sheep, we collected the uterus and embryos of the Mongolian sheep on pregnancy days 27, 56, 91 and 107 randomly for detecting by semi-quantitative RT-PCR. Then we designed the specific primers and Taq Man probes to detect enJSRV of its receptor HYAL2 mRNAs in the endometrium, chorine, placenta and embryos of different gestational age (30d, 50d, 70d, 90d, 110d and 130d) of Mongolian sheep by real-time quantitative RT-PCR. And we labeled the digoxigenin probes for localization enJSRV and its receptor HYAL2 mRNAs in the endometrium, chorine, placenta and embryos of different gestational age (30d, 50d and 130d) of Mongolian sheep.The results showed that:(1) Initial RT-PCR analyses first revealed that enJSRV and its receptor HYAL2 mRNAs is expressed in the endometrium, chorine, placenta and embryos of Mongolian sheep.(2) By Real-Time reverse transcription PCR analyses, enJSRV mRNA was found to be expressed greater in the placenta on day 90, in the endometrium on days 30 and 50, as well as in the chorine on days 70 and 110, whereas HYAL2 mRNA was no linear correlation with enJSRV. (3) In situ hybridization was used to determine the location of enJSRV and HYAL2 mRNAs. enJSRV and HYAL2 mRNAs was present in the endometrial luminal epithelium and glandular epithelium, trophoblastic giant binucleate cells, endometrial caruncle, placental cotyledons, stroma, trophectoderm, as well as in multinucleated syncytia of the placenta and blood vessel endothelial cells from all tissues regardless of gestational day. In the negative controls, no tested tissues showed positive signals when the sections were analyzed with DIG-labelled sense probes, thus confirming the specificity of the tests.In this study identification of the expression of enJSRV and its receptor HYAL2 was accomplished by molecular technology, The results of this study provide the directly demonstration of the expression of enJSRV and its receptor HYAL2 with somewhat wider pattern of cellular distribution in the endometrium, chorine, placenta and embryos of the Mongolian sheep. The dynamic and differential expression patterns of enJSRV and HYAL2 during pregnancy indicates that they are involved reciprocally in placental development and uterine remodelling. In mammals, enJSRV and HYAL2 coordinate control in promoting placental morphogenesis and regulate normal uterine development during gestation. Moreover, enJSRV and HYAL2 play a biological role during ontogenesis in the embryos. These novel results provide powerful support for the hypothesis that enJSRV and its receptor HYAL2 might have beneficial physiological roles for the host. In summary, the results make it worthy to evaluate the potential implication of enJSRV. Evidence for the enJSRV within the pregnancy sheep paves the way for further studies on the role of this molecule in placenta function.
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