piRNAs: nature, biogenesis, regulation, and their potential clinical utility

RNAs that interact with PIWI (P-element Induced Wimpy) proteins, called piRNAs, were discovered in 2006. Considered the "guardians of the genome," piRNAs were first described in germ cells of Mus musculus and Drosophila melanogaster. Since then, studies have focused on elucidating their origin, biogenesis, and mechanisms of action. Today, we know some of the molecules that participate in these processes, but the nature of the molecular processes that they perform remains largely unknown. However, recent studies have demonstrated that both the piRNAs and their associated proteins are also expressed in somatic cells, suggesting that their scope of action is much greater than initially thought. In addition, their union to PIWI proteins generates a silencing complex that represses the transcriptional and post-transcriptional expression of repeated sequences, including elements known as "transposables". Finally, a recent discovery revealed that this complex could modulate the silencing of specific messenger RNAs (mRNA) necessary for cell regulation. The regulatory function that piRNAs perform in various cellular processes has led to a diversification in their study concerning various diseases, including cancer, where there are indications of their potential function as diagnostic tools, biomarkers for prognoses, and future therapeutic targets. Recently, changes in piRNAs expression have been observed in diseases related to air pollution exposition, such as respiratory diseases.