CRISPR-Induced Expression of N-Terminally Truncated Dicer in Mouse Cells

RNA interference (RNAi) designates sequence-specific mRNA degradation mediated by small RNAs generated from long double-stranded RNA (dsRNA) by RNase III Dicer. RNAi appears inactive in mammalian cells except for mouse oocytes, where high RNAi activity exists because of an N-terminally truncated Dicer isoform, denoted Dicer(O). Dicer(O) processes dsRNA into small RNAs more efficiently than the full-length Dicer expressed in somatic cells. Dicer(O) is expressed from an oocyte-specific promoter of retrotransposon origin, which is silenced in other cell types. In this work, we evaluated CRISPR-based strategies for epigenetic targeting of the endogenous Dicer gene to restore Dicer(O) expression and, consequently, RNAi. We show that reactivation of Dicer(O) expression can be achieved in mouse embryonic stem cells, but it is not sufficient to establish a robust canonical RNAi response.