The piRNA Pathway Guards the Germline Genome Against Transposable Elements

摘要

Transposable elements (TEs) have the capacity to replicate and insert into new genomic locations. This contributs significantly to evolution of genomes, but can also result in DNA breaks and illegitimate recombination, and therefore poses a significant threat to genomic integrity. Excess damage to the germ cell genome results in sterility. A specific RNA silencing pathway, termed the piRNA pathway operates in germ cells of animals to control TE activity. At the core of the piRNA pathway is a ribonucleoprotein complex consisting of a small RNA, called piRNA, and a protein from the PIWI subfamily of Argonaute nucleases. The piRNA pathway relies on the specificity provided by the piRNA sequence to recognize complementary TE targets, while effector functions are provided by the PIWI protein. PIWI-piRNA complexes silence TEs both at the transcriptional level - by attracting repressive chromatin modifications to genomic targets - and at the posttranscriptional level - by cleaving TE transcripts in the cytoplasm. Impairment of the piRNA pathway leads to overexpression of TEs, significantly compromised genome structure and, invariably, germ cell death and sterility.