Research Note: A Rapid Method for the Detection of the Rous-Associated Endogenous Solitary Long Terminal Repeat, ev 15
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A rapid method has been developed for the detection of the solitary long terminal repeat ev15, a member of the avian leukosis virus (ALV) family of endogenous viral elements (ev genes) in chickens. Detection is accomplished by a polymerase chain reaction (PCR) assay that can be performed on purified genomic DNA samples or crude preparations of partially purified whole blood lysates. The test discriminates unambiguously between birds that are homozygous ev15-, homozygous ev15+, or heterozygous ev15-/ev15+. The incorporation of a modified touchdown amplification profile significantly improved the specificity of the PCR assay. Small-scale screening of birds from a variety of chicken breeds has revealed that ev15 is present in populations of both egg-strain birds and broilers.Keywords:
genomic DNA
Endogenous retrovirus
A new family of avian retroviral endogenous sequences designated ev/J or EAV-HP has been identified recently. Here an additional avian ev/J 4.1 endogenous sequence, ev/J 4.1 Rb, is reported. ev/J 4.1 Rb has the most extensive amino acid identity ever described for an endogenous envelope protein with the ALV-J avian leukosis virus. Here, we also demonstrate that ev/J 4.1 Rb functionally pseudotypes murine leukaemia virions and leads to a complete reciprocal interference with ALV-J envelopes. This is the first demonstration of such a high level of envelope interference between endogenous and exogenous avian retroviruses. Our results provide additional clues on the co-evolution of retroviral sequences among vertebrates.
Endogenous retrovirus
Viral Interference
Envelope (radar)
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Two human endogenous retroviruses of the HERV-W family can act as cofactors triggering multiple sclerosis (MS): MS-associated retrovirus (MSRV) and ERVWE1. Endogenous retroviral elements are believed to have integrated in our ancestors’ DNA millions of years ago. Their involvement in the pathogenesis of various diseases, including neurodegenerative pathologies, has been demonstrated. Numerous studies have shown a correlation between the deterioration of patients’ health and increased expression of endogenous retroviruses. The exact causes and mechanisms of endogenous retroviruses activation remains unknown, which hampers development of therapeutics. In this review, we will summarize the main characteristics of human endogenous W retroviruses and describe the putative mechanisms of activation, including epigenetic mechanisms, humoral factors as well as the role of the exogenous viral infections.
Endogenous retrovirus
Pathogenesis
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Retrovirus genomes exist as endogenous genetic elements in the cells of many species used in biomedical research. Many cell lines spontaneously release virus, and other cells are induced to do so by procedures commonly used in research laboratories. The expression of endogenous retroviruses can affect the results of seemingly unrelated experiments. Some retroviruses endogenous to animals grow avidly in human cells. They are not known to be hazardous to man, but further studies are necessary.
Endogenous retrovirus
Genetically engineered
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A sensitive and quantitative biological assay has been utilized to measure the ability of the exogenous and endogenous avian retroviral long terminal repeats (LTR) to promote gene expression in avian cells. This assay has revealed that the exogenous virus RAV-2 LTR is approximately equal to 10-fold more active than the LTRs of endogenous viruses RAV-0, ev-1, and ev-2. The endogenous viral LTRs show approximately equal activity. Upstream flanking cellular or viral sequences have no significant modulating effect on gene expression in our assay. Unexpectedly, we have detected and localized an additional defect outside of the LTR in the 5' noncoding leader sequence of ev-1 that further decreases gene expression relative to RAV-0 by approximately equal to 10-fold.
Endogenous retrovirus
Viral Interference
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Mammalian genomes have accumulated millions of retrotransposed sequences during evolution. This material can be divided into long terminal repeat (LTR) retrotransposons that include the endogenous retroviruses (ERVs), as well as long and short retrotransposons lacking LTRs, known as LINEs and SINEs, respectively. ERVs are defined as inherited genetic elements closely resembling the proviruses formed following exogenous retrovirus infection. In this chapter we describe the discovery, classification, and origins of ERVs in mammals, consider cellular mechanisms that have evolved to control their expression, and discuss the biological consequences, both positive and negative from the host's standpoint, of ERV inheritance.
Retrotransposon
Endogenous retrovirus
Inheritance
Retroposon
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Retroviruses integrate a reverse transcribed double stranded DNA copy of their viral genome into the chromosomal DNA of cells they infect. Occasionally, exogenous retroviruses infect germ cells and when this happens a profound shift in the virus host dynamic occurs. Retroviruses maintained as hereditable viral genetic material are referred to as endogenous retroviruses (ERVs). After millions of years of co-evolution with their hosts many human ERVs retain some degree of function and a few have even become symbionts. Thousands of copies of endogenous retrovirus long terminal repeats (LTRs) exist in the human genome. There are approximately 3000 to 4000 copies of the ERV-9 LTRs in the human genome and like other solo LTRs, ERV-9 LTRs can exhibit distinct promoter/enhancer activity in different cell lineages. It has been recently reported that a novel transcript of p63, a primordial member of the p53 family, is under the transcriptional control of an ERV-9 LTR [1]. The expression of different p63 transcript isoforms has been previously shown to have an important role in replenishing cutaneous epithelial stem cells and maintaining the fidelity of the female germ line [2]. In this recent report, a novel p63 transcript, designated GTAp63, is described as specifically expressed in healthy human testes and germ cell precursors of human testes but not in testicular cancer cells. The ability of ERV-9 regulatory regions to contribute to the maintenance of male germ line stability is yet another example of how ERVs have evolved to serve an important function in the physiology of their human hosts.
Endogenous retrovirus
Retrotransposon
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Endogenous retrovirus
Subfamily
Transcription
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Endogenous retrovirus
Provirus
Retrotransposon
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Endogenous retrovirus
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Porcine endogenous retroviruses (PERVs) in the pig genome represent a potential risk of infection in pig-to-human transplantation and are transmitted vertically. The solitary long terminal repeat (LTR) elements of the PERVs affect the replication properties of the individual viruses via their repeat sequences and by encoding a set of specific transcription factors. We examined the promoter activities of solitary LTR elements belonging to the PERV-A and -B families of the Korean domestic pig (KDP) using luciferase reporters. Three of the LTR structures (of PERV-A5-KDP, PERV-A7-KDP, PERV-A8-KDP) had different promoter activities in human HCT116 cells and monkey Cos7 cells, and potential negatively and positively acting regions affecting transcription were identified by deletion analysis. These data suggest that specific sequences in the U3 region of a given LTR element can affect the activities of promoter or enhancer elements in the PERV.
Endogenous retrovirus
Xenotransplantation
Transcription
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