Adenylation of Maternally Inherited MicroRNAs by Wispy

• Maternally inherited miRNAs are highly adenylated in oocytes and early embryos
• Adenylation of maternal miRNAs is conserved in fly, sea urchin, and mouse
• Wispy catalyzes miRNA adenylation and reduces miRNA abundance in fly
• Adenylation may contribute to the clearance of maternal miRNAs in early embryos

SummaryEarly development depends heavily on accurate control of maternally inherited mRNAs, and yet it remains unknown how maternal microRNAs are regulated during maternal-to-zygotic transition (MZT). We here find that maternal microRNAs are highly adenylated at their 3′ ends in mature oocytes and early embryos. Maternal microRNA adenylation is widely conserved in fly, sea urchin, and mouse. We identify Wispy, a noncanonical poly(A) polymerase, as the enzyme responsible for microRNA adenylation in flies. Knockout of wispy abrogates adenylation and results in microRNA accumulation in eggs, whereas overexpression of Wispy increases adenylation and reduces microRNA levels in S2 cells. Wispy interacts with Ago1 through protein-protein interaction, which may allow the effective and selective adenylation of microRNAs. Thus, adenylation may contribute to the clearance of maternally deposited microRNAs during MZT. Our work provides mechanistic insights into the regulation of maternal microRNAs and illustrates the importance of RNA tailing in development.

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