Abstract
The PIWI-interacting RNA (piRNA) pathway mainly consists of evolutionarily conserved protein factors. Intriguingly, many mutations of piRNA pathway factors lead to meiotic arrest during spermatogenesis. The majority of piRNA factor-knockout animals show arrested meiosis in spermatogenesis, and only a few show post-meiosis male germ cell arrest. It is still unclear whether the majority of piRNA factors expressed in spermatids are involved in long interspersed nuclear element-1 repression after meiosis, but future conditional knockout research is expected to resolve this. In addition, recent hamster knockout studies showed that a piRNA factor is necessary for oocytes—in complete contrast to the findings in mice. This species discrepancy allows researchers to reexamine the function of piRNA in female germ cells. This mini-review focuses on the current knowledge of protein factors derived from mammalian knockout studies and summarizes their roles in the biogenesis and function of piRNAs.
Highlights
PIWI-interacting RNAs are a distinct class of small RNAs [generally 24–31 nucleotides long] that are highly expressed in mouse testes
Reduced GTSF1 protein, which colocalizes with TDRD9 and MIWI2 in piP-bodies, resulted in target RNA remaining unsliced at the cleavage site for MILIdirected secondary PIWI-interacting RNA (piRNA) processing (Yoshimura et al, 2018)
Previous studies using knockout mice have revealed the formation of piRNA in mammals and its role in male germ cells
Summary
The majority of piRNA factor-knockout animals show arrested meiosis in spermatogenesis, and only a few show post-meiosis male germ cell arrest. Recent hamster knockout studies showed that a piRNA factor is necessary for oocytes—in complete contrast to the findings in mice. This species discrepancy allows researchers to reexamine the function of piRNA in female germ cells. This mini-review focuses on the current knowledge of protein factors derived from mammalian knockout studies and summarizes their roles in the biogenesis and function of piRNAs
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