Human endogenous retrovirus K14C drove genomic diversification of the Y chromosome during primate evolution.

The male-specific region of Y chromosome (MSY) has accumulated a higher density of human endogenous retroviruses (HERVs) and related sequences when compared with other regions of the human genome. Here, we focused on one HERV family, HERV-K14C that seemed to integrate preferentially into the Y chromosome in humans. To identify every copies of HERV-K14C in the human genome, we applied computational screening to map precisely the locus of individual HERV-K14C copies. Interestingly, 29 of all 146 copies were located in Y chromosome, and these 29 copies were mostly dispersed in the palindromic region. Three distinct HERV-K14C-related transcripts were found and were exclusively expressed in human testis tissue. Based on our phylogenetic analysis of the solitary LTRs derived from HERV-K14C on the Y chromosome we suggested that these sequences were generated as pairs of identical sequences. Specifically, analysis of HERV-K14C-related sequences in the palindromic region demonstrated that the Y chromosomal amplicons existed in our common ancestors and the duplicated pairs arose after divergence of great apes approximately 8-10 million years ago. Taken together, our observation suggested that HERV-K14C-related sequences contributed to genomic diversification of Y chromosome during speciation of great ape lineage.

Insertional polymorphisms of endogenous feline leukemia viruses.

The number, chromosomal distribution, and insertional polymorphisms of endogenous feline leukemia viruses (enFeLVs) were determined in four domestic cats (Burmese, Egyptian Mau, Persian, and nonbreed) using fluorescent in situ hybridization and radiation hybrid mapping. Twenty-nine distinct enFeLV loci were detected across 12 of the 18 autosomes. Each cat carried enFeLV at only 9 to 16 of the loci, and many loci were heterozygous for presence of the provirus. Thus, an average of 19 autosomal copies of enFeLV were present per cat diploid genome. Only five of the autosomal enFeLV sites were present in all four cats, and at only one autosomal locus, B4q15, was enFeLV present in both homologues of all four cats. A single enFeLV occurred in the X chromosome of the Burmese cat, while three to five enFeLV proviruses occurred in each Y chromosome. The X chromosome and nine autosomal enFeLV loci were telomeric, suggesting that ectopic recombination between nonhomologous subtelomeres may contribute to enFeLV distribution. Since endogenous FeLVs may affect the infectiousness or pathogenicity of exogenous FeLVs, genomic variation in enFeLVs represents a candidate for genetic influences on FeLV leukemogenesis in cats.

Dynamics of a human interparalog gene conversion hotspot.

Gene conversion between paralogs can alter their patterns of sequence identity, thus obscuring their evolutionary relationships and affecting their propensity to sponsor genomic rearrangements. The details of this important process are poorly understood in the human genome because allelic diversity complicates the interpretation of interparalog sequence differences. Here we exploit the haploid nature of the Y chromosome, which obviates complicating interallelic processes, together with its known phylogeny, to understand the dynamics of conversion between two directly repeated HERVs flanking the 780-kb AZFa region on Yq. Sequence analysis of a 787-bp segment of each of the HERVs in 36 Y chromosomes revealed one of the highest nucleotide diversities in the human genome, as well as evidence of a complex patchwork of highly directional gene conversion events. The rate of proximal-to-distal conversion events was estimated as 2.4 x 10(-4) to 1.2 x 10(-3) per generation (3.9 x 10(-7) to 1.9 x 10(-6) per base per generation), and the distal-to-proximal rate as about one-twentieth of this. Minimum observed conversion tract lengths ranged from 1 to 158 bp and maximum lengths from 19 to 1365 bp, with an estimated mean of 31 bp. Analysis of great ape homologs shows that conversion in this hotspot has a deep evolutionary history.

The Y chromosome: a graveyard for endogenous retroviruses.

We have isolated 20 different human endogenous retroviruses (ERV) related to ERV3, Hsrirt and Humer 4-1. Phylogeny and the presence of these ERV among different primates were determined by computer and Southern blot analyses. Preferential localization of ERV to the human, chimpanzee and orangutan Y chromosomes among the low-copy-number ERV is demonstrated. The reason for this accumulation of ERV on the strongly heterochromatic Y chromosome is probably mediated by (i) the absence of recombination of the Y chromosome that makes it more difficult for sequences to be lost, and (ii) integration of retroviruses in heterochromatic regions is less harmful to the organism. If ERV located on the Y chromosome are transcribed and translated to peptides, such peptides could be potential HY-antigens.