Editorial: Mobile Genetic Elements in Cellular Differentiation, Genome Stability, and Cancer

摘要

The human genome, as well as the genome of most organisms, harbors various types and abundances of transposable element derived repeats (Lander, 2001; Waterston et al., 2002).The topic on: “Mobile Genetic Elements in Cellular Di?erentiation, Genome Stability, and Cancer,” includes a collection of original research articles and reviews, which address the impact of reverse transcriptases, including the ones coded by transposable elements, on both basic biological mechanisms and disease.In 1970, the discovery of reverse transcriptases or RNA-dependent DNA polymerases, was reported by two di?erent laboratories (Baltimore, 1970; Temin and Mizutani, 1970).Since then numerous studies regarding retroviral reverse transcriptases have signi?cantly contributed to the characterization and biology of may di?erent retrovirus and retroelements.These studies continue to be of interest for the prevention and treatment of various retroviral induced human diseases and for the basic understanding of the origin of retroviruses.In addition the knowledge of reverse transcription has been harnessed for basic use in molecular biology and other applications, including recent widely used methods such as RNAseq.Asretrovirusesareconsideredexogenouslyderivedreversetranscriptases,thesubsequentdiscovery in 1987 of telomerase, also considered an endogenous RNA-dependent DNA polymerase, has signi?cantly contributed to the understanding of one of the predominant mechanisms of telomere maintenancethatcontributestomost,butnotallorganismswithlinearchromosomes(Greiderand Blackburn, 1985; Biessmann et al., 1990).Yet, sequences encoding for endogenous RNA-dependent DNA polymerases are not limited to telomerase.The isolation and subsequent genetic, biochemical, and molecular characterization of human full-length non-Long Terminal Repeat (LTR) retrotransposons, termed Long Interspersed Elements (LINE-1) demonstrated thatelements formally encode a reverse transcriptase activity (Dombroski et al., 1991; Mathias et al., 1991; Feng et al., 1996; Moran et al., 1996).Non-LTR retrotransposons are not limited to the human genome, and are present as full-length and/or truncated, rearranged, inactive remnants in many other genomes.In addition, the reverse transcriptase activities encoded by non-LTR retrotransposons share sequence identity with many other reverse transcriptases (Nakamura et al., 1997; Malik et al., 1999).Furthermore, non-LTR retrotransposons rely on the encoded reverse transcriptase for integration, typically by target-primed reverse transcription (TPRT), which was initially biochemically de?ned using the non-LTR retrotransposon R2Bm, from Bombyx mori (Luan et al., 1993).A review by Onozawa and Aplan included in this topic, describes two di?erent types of LINE-1 reverse transcriptase-mediated template sequence insertion polymorphisms (TSIPs), or integration structures that are polymorphic in the human genome (Onozawa and Aplan).