PiRNA

RNA silencing

piRNA has a role in RNA silencing via the formation of an RNA-induced silencing complex (RISC). piRNAs interact with piwi proteins that are part of a family of proteins called the Argonautes. These are active in the testes of mammals and are required for germ-cell and stem-cell development in invertebrates. Three piwi subfamily proteins – MIWI, MIWI2, and MILI – have been found to be essential for spermatogenesis in mice. piRNAs direct the piwi proteins to their transposon targets. A decrease or absence of PIWI gene expression is correlated with an increased expression of transposons. Transposons have a high potential to cause deleterious effects on their hosts and, in fact, mutations in piRNA pathways have been found to reduce fertility in D. melanogaster. Further, it is thought that piRNA and endogenoussmall interfering RNA (endo-siRNA) may have comparable and even redundant functionality in transposon control in mammalian oocytes.