[Molecular mechanisms of genetic transposition inhibition by piRNA].

Transposable elements (TEs) are DNA elements that can change their position within or between chromosomes. Most active TEs are retrotransposons, which transpose through a RNA intermediate. Since retrotransposons comprise high proportions in cell genomes, their frequent transposition may cause deleterious effects on the structure and function of the host cell genomes, thus causing serious genetic diseases such as cancer. Host cells therefore developed defense strategies to restrict these mobile elements. piRNA, which belongs to non-coding interfering RNAs, can efficiently decrease the level of retrotransposon RNA intermediates at transcriptional or post-transcriptional stages. In this review, we summarize the progress in mechanisms of piRNA-mediated retrotransposon inhibition. We hope that this review may shed light on the research of transposon and genome regulation.

The function of LINE-1-encoded reverse transcriptase in tumorigenesis.

The retrotransposon LINE-1 is the largest transposon family of humans with an estimated 500 000 copies representing 17% of the human genome. Meanwhile, it is also the sole autonomous transposon in humans. The reverse transcriptase encoded by LINE-1 is the key component required for its transposition process. Recent evidence suggests that the LINE-1-encoded reverse transcriptase is involved in many important physiological and pathological processes including tumorigenesis. The inhibition of LINE-1-encoded reverse transcriptase inhibits tumor progression, restores cancer cell differentiation and reprograms global transcription profiles. In this review, we summarize newly emerged evidence, and conclude that the LINE-1-encoded reverse transcriptase influences tumorigenesis by shaping the non-coding RNA transcriptomic profile. We hope that this review may shed light on clinical diagnosis and drug development against cancer.