Biogenesis and Functions of PIWI-Interacting RNAs

Small-RNA-mediated gene regulation is a repeated topic in biology. Animal germ cells are characterized by an interesting small RNA mediated gene silencing mechanism known as the PIWI pathway. PIWI-interacting RNAs (piRNAs) are endogenous small noncoding RNAs that act as guardians of the genome, protecting it from invasive transposable elements in the germline. piRNAs are 25 to 33 nt in length, depending on the PIWI protein that they bind to. piRNAs derive from distinct transposons that are referred to as piRNA clusters. It remains unclear how piRNAs are generated, but potential methods have been suggested, and it is certain their biogenesis pathway is distinct from miRNA and siRNA, while rasiRNAs are a piRNA subspecies. The purpose of this review is to highlight piRNA factors, biogenesis, non-gonadal function and role of genomic integrity insights in the piRNA world