U6 snRNA pseudogenes: Markers of retrotransposition dynamics in mammals

Transposable elements comprise more than 45% of the human genome and long interspersed nuclear element 1 (LINE-1 or L1) is the only autonomous mobile element remaining acti ve. Since its identification, it has been proposed that L1 contributes to the mobilizati on and amplification of other cellular RNAs and more recently, experimental demonstra- tions of this function has been described for many transcripts such as Alu , a nonautonomous mobile element, cellular mRNAs, or small noncoding RNAs. Detailed examination of th e mobilization of various cellular RNAs revealed distinct pathways by which they could be recruited during retrotransp osition; template choice or template switching. Here, by analyzing genomic structures and retro transposition signatures associated wi th small nuclear RNA (snRNA) sequences, we identified distinct recruiting steps during the L1 retro transposition cycle for the formation of snRNA-processed pseudogenes. Interestingly, some of the identified recruiting steps take place in the nucleus. Moreover, after comparison to other vertebrate genomes, we established that snRNA a mplification by template switching is common to many LINE families from several LINE clades. Finally, we suggest that U6 snRNA copies can serve as markers of L1 retrotransposition dynamics in mammalian genomes. (Résumé d'auteur