engleski

A retrotransposon-driven Dicer isoform directs endogenous siRNA production in mouse oocytes

In mammals, a single Dicer participates in biogenesis of small RNAs in microRNA (miRNA) and RNA interference (RNAi) pathways. In mice, endogenous RNAi is highly active in oocytes but not in somatic cells, which we ascribe here to an oocyte-specific Dicer isoform (DicerO). DicerO lacks N-terminal DExD helicase domain and has higher cleavage activity than the fulllength Dicer in somatic cells (DicerS). Unlike DicerS, DicerO efficiently produces small RNAs from long dsRNA substrates. Expression of DicerO isoform is driven by an intronic MT-C retrotransposon promoter, deletion of which causes loss of DicerO and female sterility. Oocytes from females lacking the MT-C element show meiotic spindle defects and increased levels of endo-siRNA, copying the maternal Dicer null phenotype. The alternative Dicer isoform, whose phylogenetic origin demonstrates evolutionary plasticity of RNA silencing pathways, is the main determinant of endogenous RNAi activity in the mouse female germline.

oocyte development; retrotransposon; RNA-Seq; Dicer

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