Roles and mechanisms of piRNAs in self-renewal and differentiation of germline stem cells

Abstract

piRNAs are considered to be plentiful and heterogeneous non-coding RNAs, playing a significant role in embryonic patterning and stem cells. In recent research, scientists have explored how piRNAs contribute to both biological processes and roles in stem cells. Their regulatory action is essential for enabling stem cells to both renew themselves and differentiate into specialized types. piRNAs mediate transposable element (TE) silencing to ensure gene integrity via epigenetic repression mechanisms, ‘ping-pong’ mechanism, and splicing. Recent findings reveal that piRNAs are involved in silencing TE and regulating protein-coding mRNAs. This regulation suppresses the target mRNAs either via cleavage mediated by PIWI proteins or through recruiting the CCR4-NOT complex. Thereby the processes of stem cell self-renewal and differentiation have been lightened. piRNAs together with PIWI proteins contribute to controlling the translation of factors. As biological translation regulators, piRNAs in germline stem cells (GSCs) can trigger cell fate by specific regulation of mRNA targets. This role of piRNAs in regulating translation appears to be conserved across stem cells and is likely essential for maintaining stem cell balance. Furthermore, piRNAs along with PIWI proteins can be the biomarkers of stem cells. This review concentrates on recent findings that explore the developmental and biological functions of piRNAs, with a particular emphasis on their contributions to early embryonic organization and the regulation of stem cell behavior.