Endogenous retroviruses

Abstract

Endogenous retroviruses (ERVs) most likely are remnants of ancient retroviral infections. ERVs preserve functions of exogenous retroviruses to a varying extent, and can be parasites, symbionts or more or less neutral genetic 'junk'.Their evolution has two facets, pre- and post-endogenization. Although the two are not clearly separated, the first pertains to retroviral evolution in general and the second to the fate of repetitive DNA and the evolution of the host organism and its genome. The study of ERVs provides much material for the understanding of retroviral evolution. This sequence archive reflects the history of successes and shortcomings of antiviral resistance, but also of strategic evolutionary decisions regarding genome organization and new gene acquisition. This review discusses retroviral evolution illustrated through HERVs, bioinformatic prerequisites for ERV studies, the endogenization process and HERV evolution post-endogenization, including relation to disease. (Part of a multi-author review).

Placenta-specific Expression of the Interleukin-2 (IL-2) Receptor β Subunit from an Endogenous Retroviral Promoter

“…Numerous studies have found that the placenta is generally permissive to transcription initiating from LTRs, and some ERV copies are expressed at higher levels in placenta than other tissues (4,10,11). In fact, ERVs may have been central in the evolution of placental mammals, and domestication of ERV proteins has led to their serving important functions in this tissue (12)(13)(14).…”

Endogenous Retroviral-Like Aspartic Protease, SASPase as a Key Modulator of Skin Moisturization

“…Interestingly, the SASPase gene is only found in the mammalian genome. Although it has not been proven that the SASPase gene in mammals is derived from an ancient retroviral infection into the germline, this molecular mechanism would be the fi rst example of a virus-related element that has contributed to the evolution of vertebrate skin [ 7,70 ] . Therefore, the study of the SASPase physiological function should provide valuable clues that reveal the role of the SC in mammals and how they adapted to life on land.…”

Endogenous retrovirus sequences as a novel class of tumor-specific antigens: an example of HERV-H env encoding strong CTL epitopes

“…HERVs posses a single open reading frame containing the genes gag, pol and env, which are Xanked by LTRs at the 5Ј and 3Ј ends [5,6]. For the most part, the interplay between mutations [3], epigenetic mechanisms and posttranscriptional regulations silence HERV expression [2,7]. Yet, there are some examples of HERVs executing preserved functions as do the proviruses of their exogenous ancestors, making them something between parasites and symbionts.…”

“…The process of endogenization is dependant on the viruses' ability to withstand restrictions common to all cells, their potential to infect reproductive tissues, that is, cells of the germ line and Wnally to proceed to Wxation in the human genome. All these processes must happen without loss of Wtness of the host, thus excluding highly pathogenic ERV [2]. Generally, HERVs are classiWed into three groups: class I (gamma (like) retroviruses), class II (beta (like) retroviruses) and class III (spuma (like) retroviruses) [2,3].…”

“…All these processes must happen without loss of Wtness of the host, thus excluding highly pathogenic ERV [2]. Generally, HERVs are classiWed into three groups: class I (gamma (like) retroviruses), class II (beta (like) retroviruses) and class III (spuma (like) retroviruses) [2,3]. The most common nomenclature utilizes the single-letter amino acid code corresponding to the tRNA primer that is used for reverse transcription of the HERV genome [4].…”