Adenylation of maternally inherited microRNAs by Wispy

Early development depends heavily on accurate control of maternally inherited mRNAs, and yet it remains unknown how maternal microRNAs (miRNAs) are regulated during maternal to zygotic transition (MZT). We here find that maternal miRNAs are highly adenylated at their 3' ends in mature oocytes and early embryos. Pervasive adenylation is observed in oocytes of fly, sea urchin and mouse, indicating that maternal miRNA adenylation may be widely conserved in animals. We identify Wispy as the enzyme responsible for miRNA adenylation in flies. Wispy is known to be expressed specifically in oocytes and early embryos and function as a noncanonical poly(A) polymerase. Knockout of wispy abrogates miRNA adenylation and induces miRNA accumulation in fly eggs whereas overexpression of Wispy increases adenylation and reduces miRNA levels in S2 cells. Adenylation occurs on both the 5p and 3p miRNAs, indicating that Wispy acts on miRNAs after Dicer processing. We further find that Wispy interacts with Ago1 through protein-protein interaction, which may allow the effective and selective adenylation of miRNAs. Thus, adenylation may contribute to the clearance of maternally deposited miRNAs during MZT. Our work provides the first mechanistic insights into the regulation of maternal miRNAs and illustrates the importance of RNA tailing in development. MiRNA expression and modification profile during early embryo development of fruit fly and zebra fish using high throughput sequencing