ABSTRACT
Objective: To review recent research findings on the specific expression of endogenous retroviral sequences (ERVS) in reproductive tissues and their possible physiological roles. ERVS have been implicated in several biological events such as induction of resistance to exogenous retrovirus invasion; involvement in placental trophoblast formation; sperm maturation and differentiation; and stimulation of local immunosuppression to protect the foetus from immunological attack. Data sources: Critical review of relevant articles and abstracts cited in international and local journals; literature searches on Medline and Medchem up to 2005. Data synthesis: Retroviruses have been implicated in the induction of tumour and immunological disorders. Over the years; endogenous retroviruses (ERVs) and retroviral elements have been detected in the genome of many vertebrate species; including primates. The evidence for the presence of retroviruses in the primate tissues such as the placenta; ovary; breast; testis and epididymis has been documented using electron microscopic studies. Retrovirus-like particles were found budding from the basal membrane of lyncytiotrophoblasts; as well as in tumour cell lines in embryonic carcinoma or teratocarcinomas. Apart from their pathological effects; recent evidence suggests that these ERVs may play useful roles in normal physiological events. Results: Recent studies indicate the expression of endogenous retroviruses in the testis; epididymis; placenta and breast. However; limited data exist on the detection of ERVs in the ovary. Overall; the precise functions for ERVs in these tissues are not well understood. In the testis and epididymis; speculative functions may include among others spermatogenesis and/or sperm maturation (differentiation) whereas in placenta they are possibly associated with trophoblast fusion and locally induced immunosuppression to protect the foetus from immunological attack. Experiments in our laboratory have indicated restricted expression of retroviral antigens including baboon endogenous retroviral proteins (BERV); ERV-3; HIV-1 gp41 and HERV-K env in the baboon ovary. Conclusion: ERVs are specifically expressed in different mammalian reproductive tissues and may have unique physiological roles
Subject(s)
Retroviridae , Tumor Lysis SyndromeABSTRACT
The human genome comprises of abundant DNA sequences related to endogenous retroviruses (ERV) and a variety of solitary long terminal repeats (LTRs). Substantial numbers of intact retroviral particles have been detected by electron microscopy in normal human placental villous tissue particularly in syncytiotrophoblast. Understanding the molecular structure; organisation and distribution of these ERV sequences may lead to elucidation of their possible dual function at the foetal-maternal interface; proliferation and differentiation of cytotrophoblast and induction of local pregnancy-associated immune suppression thus allowing survival of the foetal allograft. In this study; antibody probes were used to screen a human placental expression library and cDNA clones isolated were characterized by polymerase chain reaction; Southern blot hybridisation; DNA cloning and partial nucleotide sequencing. A specific 1.7kb-cDNA clone was isolated from a human placental expression library. Further characterisation showed this clone represents a single copy gene; approximately 9-10kb and did not hybridise to the env region of ERV3 human endogenous retrovirus. The 1.7kb-cDNA clone may represent a provirus co-expressed with cellular sequences