Biomedical subjects

Sandra Blaise

Publications and source records attributed to Sandra Blaise.

6 recordsLinked to original sources

PubMed2005

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. RESULTS: To characterize further their status, we presently sequenced 12 of these genes from a panel of 91 Caucasian individuals. Genomic analyses reveal strong sequence conservation (only two non synonymous Single Nucleotide Polymorphisms [SNPs]) for the two HERV-W and HERV-FRD envelope genes, i.e. for the two genes specifically expressed in the placenta and possibly involved in syncytiotrophoblast formation. We further show--using an ex vivo fusion assay for each allelic form--that none of these SNPs impairs the fusogenic function. The other envelope proteins disclose variable polymorphisms, with the occurrence of a stop codon and/or frameshift for most--but not all--of them. Moreover, the sequence conservation analysis of the orthologous genes that can be found in primates shows that three env genes have been maintained in a fully coding state throughout evolution including envW and envFRD. CONCLUSION: Altogether, the present study strongly suggests that some but not all envelope encoding sequences are bona fide genes. It also provides new tools to elucidate the possible role of endogenous envelope proteins as susceptibility factors in a number of pathologies where HERVs have been suspected to be involved.

Alleles↗

PubMed2005

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. Conversely, the second envelope gene, named envV, discloses a placenta-specific expression, but is not fusogenic in any of the cells tested. Altogether, these results suggest that at least one of these env genes may play a role in placentation, but most probably through a process different from that of the two previously identified syncytins.

Animals↗

PubMed2005

Identification of a functional envelope protein from the HERV-K family of human endogenous retroviruses.

Genome-wide screening of sequence databases for human endogenous retroviruses (HERVs) has led to the identification of 18 coding env genes, among which two-the syncytin genes-encode fusogenic ENV proteins possibly involved in placenta physiology. Here we show that a third ENV, originating from the most "recent" HERV-K(HML2) family, is functional. Immunofluorescence analysis of env-transduced cells demonstrates expression of the protein at the cell surface, and we show that the protein confers infectivity to simian immunodeficiency virus pseudotypes. Western blot analysis of the pseudotyped virions further discloses the expected specific cleavage of the ENV precursor protein. This functional ENV could play a role in the amplification--via infection of the germ line--of the HERV-K genomic copies, all the more as coding HERV-K gag and pol genes can similarly be found in the human genome, which could therefore generate infectious virions of a fully endogenous origin.

Endogenous Retroviruses↗

PubMed2004

Identification of an envelope protein from the FRD family of human endogenous retroviruses (HERV-FRD) conferring infectivity and functional conservation among simians.

A member of the HERV-W family of human endogenous retroviruses (HERV) had previously been demonstrated to encode a functional envelope which can form pseudotypes with human immunodeficiency virus type 1 virions and confer infectivity on the resulting retrovirus particles. Here we show that a second envelope protein sorted out by a systematic search for fusogenic proteins that we made among all the HERV coding envelope genes and belonging to the HERV-FRD family can also make pseudotypes and confer infectivity. We further show that the orthologous envelope genes that were isolated from simians-from New World monkeys to humans-are also functional in the infectivity assay, with one singular exception for the gibbon HERV-FRD gene, which is found to be fusogenic in a cell-cell fusion assay, as observed for the other simian envelopes, but which is not infectious. Sequence comparison of the FRD envelopes revealed a limited number of mutations among simians, and one point mutation-located in the TM subunit-was shown to be responsible for the loss of infectivity of the gibbon envelope. The functional characterization of the identified envelopes is strongly indicative of an ancestral retrovirus infection and endogenization, with some of the envelope functions subsequently retained in evolution.

Amino Acid Sequence↗

PubMed2003

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. Cells prone to env-mediated fusion were different for the two envelopes, indicating different receptor usage. A search for the FRDenv gene in primates indicated that the corresponding proviral element is present in all simians, from New World monkeys to humans, being absent only in prosimians. Cloning of the corresponding env genes in simians disclosed conservation of the fully coding status of the gene, and most remarkably, conservation of its fusogenic property. Finally, a Northern blot analysis for the expression of the FRD family among a series of human tissues demonstrated specific expression in the placenta, as previously demonstrated for the other fusogenic human envelope of the HERV-W family. Altogether, the present data have identified a previously uncharacterized envelope (that we propose to name syncytin 2 after renaming syncytin as syncytin 1) with a potential role in placenta formation, and the identification of the complete set of retroviral envelopes with fusogenic properties now allows a definite analysis of the possible role of HERV in this physiological process, via classical genetic approaches.

Amino Acid Sequence↗

PubMed2001

The envelope of Mason-Pfizer monkey virus has immunosuppressive properties.

We have demonstrated previously that the envelope protein of a murine retrovirus, Moloney murine leukaemia virus, has immunosuppressive properties in vivo. This property was manifested by the ability of the protein, when expressed by tumour cells normally rejected by engrafted mice, to allow the env-expressing cells to escape immune rejection and to proliferate. Here, it is shown that this property is not restricted to the envelope of a murine retrovirus, but is also shared by the envelope encoded by a primate retrovirus, Mason-Pfizer monkey virus.

Amino Acid Sequence↗