Expression profiles of endogenous retroviruses in Old World monkeys.

Human endogenous retroviruses (HERVs) are a major component of the human genome and an active part of the transcriptome. Some HERVs play vital biological roles, while others potentially contribute to diseases. Many HERVs are relatively new in the primate genome, having entered or expanded after the lineages leading to the platyrrhines (New World monkeys) and catarrhines (Old World monkeys and apes) separated. Most HERVs are active in at least some tissues, though tissue specificity is common for most elements. We analyzed multiple tissues from several Old World monkeys using retroviral pol-based DNA microarrays and quantitative PCR methods to determine their ERV expression profiles. The results demonstrate that while many ERVs are active in nonhuman primates, overall the tissue expression specificity is unique to each species. Most striking is that while the majority of HERVs analyzed in this study are expressed in human brain, almost none are expressed in Old World monkey brains or are only weakly expressed.