Genetic activation of canonical RNA interference in mice [brain]

Canonical RNA interference (RNAi) is sequence-specific mRNA degradation guided by small interfering RNAs (siRNAs) made from long double-stranded RNA (dsRNA) by RNase III Dicer. RNAi has different functions in eukaryotes including gene regulation, antiviral innate immunity or defense against transposable elements. In mammals, RNAi is constrained by inefficient cleavage of dsRNA by Dicer because it is adapted to produce microRNAs, a different class of small RNAs. An exception of the rule is highly active RNAi in mouse oocytes, which employs a truncated Dicer isoform (ΔHEL1). A homozygous mutation of murine Dicer to express only the truncated variant causes major dysregulation of microRNAs and perinatal lethality. Here, we report the phenotype and RNAi activity in DicerΔHEL1/wt mice, which are viable, fertile, slightly smaller, and show minimal miRNome changes. At the same time, endogenous siRNA levels are increased by an order of magnitude in DicerΔHEL1/wt mice. We show that siRNA abundance is limited by available dsRNA but not by the Protein Kinase R, an innate immunity factor shown to limit siRNA biogenesis in cultured cells. Using dsRNA expressed from a transgene, functional RNAi in vivo was successfully induced in the heart. DicerΔHEL1/wt mice thus represent a new model for researching mammalian canonical RNAi in vivo and offer an unprecedented platform for addressing earlier claims about its biological roles. Bulk small RNA-seq of 12 mouse brain samples in four different genotypes: - 3x wt - 3x DicerSOM/wt Pkr–/– Tg(MosIR) - 3x DicerΔHEL1/wt Pkr+/– Tg(MosIR) - 3x DicerΔHEL1/wt Pkr–/– Tg(MosIR)