We characterized the human endogenous retrovirus (HERV-W) family in humans and primates. In silico expression data indicated that 22 complete HERV-W families from human chromosomes 1?3, 5?8, 10?12, 15, 19, and X are randomly expressed in various tissues. Quantitative real-time RT-PCR analysis of the HERV-W env gene derived from human chromosome 7q21.2 indicated predominant expression in the human placenta. Several copies of repeat sequences (SINE, LINE, LTR, simple repeat) were detected within the complete or processed pseudo HERV-W of the human, chimpanzee, and rhesus monkey. Compared to other regions (5?LTR, Gag, Gag-Pol, Env, 3?LTR), the repeat family has been mainly integrated into the region spanning the 5?LTRs of Gag (1398 bp) and Pol (3242 bp). FISH detected the HERV-W probe (fosWE1) derived from a gorilla fosmid library in the metaphase chromosomes of all primates (five hominoids, three Old World monkeys, two New World monkeys, and one prosimian), but not in Tupaia. This finding was supported by molecular clock and phylogeny data using the divergence values of the complete HERV-W LTR elements. The data suggested that the HERV-W family was integrated into the primate genome approximately 63 million years (Myr) ago, and evolved independently during the course of primate radiation.

Keywords: Primates, RT-PCR, FISH, Gene Expression, HERV-W Family, Human Tissues