Isolation of novel human endogenous retrovirus HC2-like elements in human chromosomes

Long terminal repeats of porcine endogenous retroviruses in Sus scrofa

Using PCR, sequencing, and bioinformatic approaches with the genomic DNAs of Korean pigs (domestic, wild, and hybrid with Yorkshire), twelve solitary PERV long terminal repeat elements were identified and analyzed. Structure analysis of the LTR elements indicated that they have different repeat sequences in the U3 region. The PERV-A6-KWP1 and -KWP2 elements bear seven and eight 39-bp repeats, respectively. The R region of the PERV LTR elements was highly conserved in pig and mouse genomes, suggesting that they seem to have originated from a common exogenous viral element and then evolved independently throughout the course of mammalian evolution.

Expression and phylogenetic analyses of human endogenous retrovirus HC2 belonging to the HERV-T family in human tissues and cancer cells

Recently, a new HERV-T family, representative of the HERV-S71 and HERV-HC2 family, was identified using a screen for envelope genes and a computer-assisted database search. Here, we investigate expression of pol fragments of HERV-HC2 belonging to the HERV-T family in various human tissues and cancer cells. The pol gene was expressed in nearly all human tissues examined and in all cancer cell lines. Expression analyses suggest that the pol gene of HERV-HC2 family is more actively transcribed in human cancer cells than in normal tissues, suggesting a functional role during carcinogenesis. Phylogenetic analysis of the HERV-HC2 pol family revealed three groups (I, II, and III) generated through evolutionary divergence during primate evolution, indicating that they were integrated into primate genomes approximately 56 million years (MY) ago and have evolved at a rate of 0.2% nucleotide differences per MY. Our data might contribute to an understanding of the information on the transcriptional and pathological potential of the HERV-T family in human disease, including cancer.

Endogenous retrovirus HERV-I LTR family in primates: sequences, phylogeny, and evolution

A human endogenous retrovirus (HERV-I; RTVL-I) has been located within the first intron of a haptoglobin-related gene. Two members of the HERV-I family were identified in proximal Yq11.2 and caused AZFa microdeletions as a result of intra-chromosomal recombination events in azoospermic patients. Using PCR25 and the sequencing approach with the genomic DNAs of primates, hominoids, Old and New World monkeys, and prosimians, the HERV-I LTR elements were identified and analysed. The LTR elements were detected only in the hominoids and the Old World monkeys, indicating that the HERV-I LTR elements were inserted into the primate genome after the split of the New World monkeys in the Oligocene era, about 33 million years ago. Nineteen members of the HERV-I LTR elements from the hominoids and the Old World monkeys showed multiple insertions or deletions. They showed a 78.6-97.4% sequence similarity to that of Hu-15 (accession no. AF290422; HERV-I LTR on human Yq11.2). The evolutionary relationships within the HERV-I LTR family among hominoids and Old World monkeys showed a random cluster, indicating that HERV-I LTR elements have evolved independently in primate evolution.

Development of broadly targeted human endogenous gammaretroviral pol-based real time PCRs Quantitation of RNA expression in human tissues

Endogenous retroviral sequences (ERVs) are dynamic genomic components with profound influences on gene expression and genomic structure. Their extent of expression is not well known. Several broadly targeted real-time reverse transcription PCR (QPCRs) systems for surveillance of RNA expression of the major groups of human gammaretroviral ERVs were constructed. The highly conserved reverse transcriptase (RT) and integrase (IN) domains of the pol gene were used as targets for the PCRs, which were both probe-based (TaqMan) and probe-less (SYBR Green). Different levels of primer and probe degeneracy, with or without inosine, were tested. Several of the PCRs had sensitivities of a few HERV nucleic acid copies per PCR reaction. Specificities were approximately as expected from the fit of primers and probes. Gammaretroviral HERV RNA expression was studied in different human tissues. Each HERV group had a specific pattern of expression. HERV-E was highly expressed in testis, HERV-I/T in brain and testis, HERV-H in brain and testis, while HERV-W was highly expressed in placenta. Gammaretroviral RNA was not detected in plasma from 50 blood donors in saliva from 20 persons. In conclusion, a set of tools for investigation of gammaretroviral HERV RNA expression was created.

Isolation and phylogeny of new endogenous retroviral sequences belonging to the HERV-F family

A new human endogenous retroviral family (HERV-F) has been identified from human chromosome 7q31.1-q31.3 that was identical to the XA34 cDNA clone isolated from a human glioma cDNA library with an ERV-9 env probe. We investigated pol gene sequences of the HERV-F family from a human monochromosomal DNA panel and analyzed these with HERV-F. The pol gene sequences of the HERV-F family were detected on chromosomes 3, 6, 7, 10, 11, 14, 19, 20, X, and Y as examined by PCR. Thirty-six pol gene sequences identified from the human chromosomes have a high degree of sequence similarity (80-99%) with that of the HERV-F. Phylogenetic analysis of pol gene sequences distinctively showed four groups, indicating that the HERV-F family could be amplified at least four times after the original integration into the human genome or represent integration events separately during hominid evolution. One clone (HFY-3) on chromosome Y shared 100% sequence identity with a clone (HF19-2) on chromosome 19, and a clone (HF20-6) on chromosome 20 suggests either a recent retrotransposition or a chromosomal translocation. The history of endogenous retroviral sequences may contribute to an understanding of evolutionary change in human genomes.

Isolation and phylogeny of endogenous retrovirus sequences belonging to the HERV-W family in primates

An investigation was undertaken of primate pol gene sequences from a novel endogenous retrovirus family, ERV-W, related to a new human endogenous retrovirus family (HERV-W) that includes multiple sclerosis-associated retrovirus (MSRV) sequences identified in particles recovered from monocyte cultures from patients with multiple sclerosis. The pol gene sequences of the ERV-W family were detected in hominoids and Old World monkeys, but not in New World monkeys, whereas ERV-W long terminal repeat-like elements were detected in all primates (hominoids, Old World monkeys and New World monkeys). Thirty-two pol gene sequences from hominoids and Old World monkeys showed a high degree of sequence identity to MSRV and other HERV-W sequences. Phylogenetic analysis indicated close relationships of pol gene sequences across primate species. The analysis suggests that the ERV-W family has evolved independently but in constrained patterns ('parallel evolution') in different primate species, including man. The ratio of synonymous to non-synonymous substitutions indicated that negative selective pressure is acting on CHW1-1 from chimpanzee, HBW6-6 from baboon and HWX5 from man, sequences that have no disruption by point mutation or insertions/deletions. Therefore, these pol gene sequences could be associated with an active provirus in primates. The findings indicate that the ERV-W family has continued to evolve in the course of the primate radiation and may include members with a capacity to influence gene function and possibly cause disease.