Drosophila YBX1 homolog YPS promotes ovarian germ line stem cell development by preferentially recognizing 5-methylcytosine RNAs

Significance 5-Methylcytosine (m5C) is one of the most abundant RNA modifications, but its function in adult stem cell development remains poorly defined. This study shows that Ypsilon schachtel (YPS) promotes germ line stem cell (GSC) maintenance, proliferation, and differentiation in the adult Drosophila ovary by preferentially binding to m5C-containing RNAs. Highly conserved cold-shock domains (CSDs) of YPS and its human homolog Y box binding protein 1 (YBX1) exhibit preferential binding to m5C-containing RNAs through hydrophobic interactions. Human YBX1 can functionally replace YPS to promote GSC development in the Drosophila ovary, and overexpressing RNA-binding–defective YBX1 and YPS mutant proteins disrupts normal GSC development. Thus, this study provides insight into the importance of m5C RNA modification in adult stem cell development. 5-Methylcytosine (m5C) is a RNA modification that exists in tRNAs and rRNAs and was recently found in mRNAs. Although it has been suggested to regulate diverse biological functions, whether m5C RNA modification influences adult stem cell development remains undetermined. In this study, we show that Ypsilon schachtel (YPS), a homolog of human Y box binding protein 1 (YBX1), promotes germ line stem cell (GSC) maintenance, proliferation, and differentiation in the Drosophila ovary by preferentially binding to m5C-containing RNAs. YPS is genetically demonstrated to function intrinsically for GSC maintenance, proliferation, and progeny differentiation in the Drosophila ovary, and human YBX1 can functionally replace YPS to support normal GSC development. Highly conserved cold-shock domains (CSDs) of YPS and YBX1 preferentially bind to m5C RNA in vitro. Moreover, YPS also preferentially binds to m5C-containing RNAs, including mRNAs, in germ cells. The crystal structure of the YBX1 CSD-RNA complex reveals that both hydrophobic stacking and hydrogen bonds are critical for m5C binding. Overexpression of RNA-binding–defective YPS and YBX1 proteins disrupts GSC development. Taken together, our findings show that m5C RNA modification plays an important role in adult stem cell development.

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