Murine endogenous retrovirus MuERV-L is the progenitor of the "orphan" epsilon viruslike particles of the early mouse embryo.

Viruslike particles which displayed a peculiar wheellike appearance that distinguished them from A-, B- or C-type particles had previously been described in the early mouse embryo. The maximum expression of these so-called epsilon particles was observed in two-cell-stage embryos, followed by their rapid decline at later stages of development and no particles detected at the zygote one-cell stage. Here, we show that these particles are in fact produced by a newly discovered murine endogenous retrovirus (ERV) belonging to the widespread family of mammalian ERV-L elements and named MuERV-L.

Comprehensive search for intra- and inter-specific sequence polymorphisms among coding envelope genes of retroviral origin found in the human genome: genes and pseudogenes.

Background: The human genome carries a high load of proviral-like sequences, called Human Endogenous Retroviruses (HERVs), which are the genomic traces of ancient infections by active retroviruses. These elements are in most cases defective, but open reading frames can still be found for the retroviral envelope gene, with sixteen such genes identified so far. Several of them are conserved during primate evolution, having possibly been co-opted by their host for a physiological role.

Functional characterization of two newly identified Human Endogenous Retrovirus coding envelope genes.

A recent in silico search for coding sequences of retroviral origin present in the human genome has unraveled two new envelope genes that add to the 16 genes previously identified. A systematic search among the latter for a fusogenic activity had led to the identification of two bona fide genes, named syncytin-1 and syncytin-2, most probably co-opted by primate genomes for a placental function related to the formation of the syncytiotrophoblast by cell-cell fusion. Here, we show that one of the newly identified envelope gene, named envP(b), is fusogenic in an ex vivo assay, but that its expression - as quantified by real-time RT-PCR on a large panel of human tissues - is ubiquitous, albeit with a rather low value in most tissues.

Genomewide screening for fusogenic human endogenous retrovirus envelopes identifies syncytin 2, a gene conserved on primate evolution.

Screening human sequence databases for endogenous retroviral elements with coding envelope genes has revealed 16 candidate genes that we assayed for their fusogenic properties. All 16 genes were cloned in a eukaryotic expression vector and assayed for cell-cell fusion by using a large panel of mammalian cells in transient transfection assays. Fusion was observed for two human endogenous retrovirus (HERV) envelopes, the previously characterized HERV-W envelope, also called syncytin, and a previously uncharacterized gene from the HERV-FRD family.

Survey of human genes of retroviral origin: identification and transcriptome of the genes with coding capacity for complete envelope proteins.

Sequences of retroviral origin occupy approximately 8% of the human genome. Most of these "retroviral" genes have lost their coding capacities since their entry into our ancestral genome millions of years ago, but some reading frames have remained open, suggesting positive selection. The complete sequencing of the human genome allowed a systematic search for retroviral envelope genes containing an open reading frame and resulted in the identification of 16 genes that we have characterized.

The full-length envelope of an HERV-H human endogenous retrovirus has immunosuppressive properties.

We have demonstrated previously that the envelope proteins of a murine retrovirus (Moloney murine leukaemia virus) and a simian retrovirus (Mason-Pfizer monkey virus) have immunosuppressive properties in vivo. This property was manifested by the ability of the proteins, when expressed by tumour cells normally rejected by engrafted mice, to allow the envelope-expressing cells to escape immune rejection and to proliferate. Here, it is shown that this property is not restricted to the envelope of infectious retroviruses, but is also shared by the envelope protein encoded by an endogenous retrovirus of humans belonging to the HERV-H family.