User:Amelia1108/sandbox

Hyaluronidase 2
HYAL2 is part of a large hyaluronglucosaminidase family however it exhibits very low hyaluronidase activity, and serves as the cellular receptor cell-surface protein for JSRV entry HYAL2 mRNA is expressed in the binucleate cells and multinucleated syncytia of the sheep placenta, but is not observed in the maternal uterus. In situ hybridization analysis revealed that HYAL2 mRNA was only detected in the binucleate cells and multinucleated syncytial plaques That there is co-expression of enJSRV Env and HYAL2 in the same cell types supports the hypothesis that HYAL2 binds to enJSRVs Env on the binucleate cells and promotes their fusion into multinucleated syncytia

Comparative physiology in humans and mice
Of interest for comparative physiology is that the presence of enJSRV envelope (env) protein expression in the developing sheep placenta is very similar to that observed for syncytin in humans and mouse During the formation of the syncytiotrophoblast of the human placenta by fusion of mononuclear cytotrophoblasts, human syncytins are specifically expressed. The syncytins are fusogenic when expressed in vitro, supporting the hypothesis that they are involved in placental morphogenesis. These observations support the theory that an ancient retroviral infection had important consequences for mammalian evolution. The involvement of the betaretrovirus enJSRV in the sheep conceptus trophoblasts further argues for its involvment in sheep placentation

Future directions and summary
Research surrounding endogenous retroviruses supports the idea that they may play critical roles in conceptus growth, placental differentiation and cell fusion in mammals. The morphological aspecets of binucleate cell differentiation in ruminants such as sheep are well characterised, but the mechanisms are not well defined - though evidence shows that enJSRV RNA and HYAL2 mRNA are co-expressed in the binucleate cell and multinucleated syncytiotrophoblasts throughout gestation