Distribution of human endogenous retroviral RTVL-H2 LTR sequences among human chromosomes

Retroviruses and primate evolution

Human endogenous retroviruses (HERVs), probably representing footprints of ancient germ-cell retroviral infections, occupy about 1% of the human genome. HERVs can influence genome regulation through expression of retroviral genes, either via genomic rearrangements following HERV integrations or through the involvement of HERV LTRs in the regulation of gene expression. Some HERVs emerged in the genome over 30 MYr ago, while others have appeared rather recently, at about the time of hominid and ape lineages divergence. HERVs might have conferred antiviral resistance on early human ancestors, thus helping them to survive. Furthermore, newly integrated HERVs could have changed the pattern of gene expression and therefore played a significant role in the evolution and divergence of Hominoidea superfamily. Comparative analysis of HERVs, HERV LTRs, neighboring genes, and their regulatory interplay in the human and ape genomes will help us to understand the possible impact of HERVs on evolution and genome regulation in the primates. BioEssays 22:161-171, 2000.

Identification and phylogenetic analysis of novel human endogenous retroviral sequences belonging to the HERV-H family on human X and Y chromosomes

HERV-H, a family of endogenous retroviral elements that has undergone successive expansions in the human genome, includes sequences that are expressed in placenta and T cells. With a PCR approach to the HERV-H using human monochromosomal somatic cell hybrid DNA, we identified 8 new HERV-H sequences on the X chromosome, and one novel HERV-H element, HY-1, the first reported such element on the Y chromosome, and compared these with sequences in the nucleotide sequence database. Phylogenetic analysis indicated that clone HX-1 and BAC clone 523A23 on the X chromosome were found to be in close relationship to the sequences of DJ088A21 on the human chromosome 7q31. This finding allows us to speculate that HERV-H elements may have evolved by intra-chromosomal spread. Our data may relevant to an understanding of human genomic plasticity.

Perpetually mobile footprints of ancient infections in human genome

Up to 1% of the human genome is represented by human endogenous retroviruses (HERVs) and their fragments that are likely footprints of ancient primate germ-cell infections by retroviruses that occurred 10-60 million years ago. HERV solitary long terminal repeats (LTRs) can be often met in close vicinity to functional genes. The LTRs comprise a set of regulatory sequences like promoters, enhancers, hormone responsive elements and polyadenylation signals that might come out as new regulatory signals to resident genes and thus change their regulation in evolution. Moreover, the LTRs have a potential for chromatin remodeling that can also modulate gene expression. This review describes the integration specificity and distribution of the HERVs and LTRs in the human genome and discusses possible functional consequences of their integration in the vicinity of genes.