The Role of Dicer in Post-mitotic Dopaminoceptive Neurons and Turnover of Dicer

In this work, we explored the role of Dicer, an RNase III enzyme that is central to the production of mature microRNAs (miRNAs), in dopaminoceptive neurons of mice, as well as the turnover of the miRNAs Dicer generates. MiRNAs are small non-coding RNAs that can act to repress target mRNAs by suppressing translation and/or reducing mRNA stability. While it is clear that miRNAs and Dicer have a role in the early development of neurons, their roles in the post-mitotic neuron in vivo are largely unknown. To determine the roles of Dicer in neurons, we ablated Dicer in dopaminoceptive neurons. Mice that have lost Dicer in these cells display a range of phenotypes including ataxia, front and hind limb clasping, reduced brain size and smaller neurons. Surprisingly, dopaminoceptive neurons without Dicer survive over the life of the animal. Another fascinating aspect of this study is that some miRNAs persisted in the brains of the mice, weeks after Dicer loss. A largely unexplored question is how are miRNAs turned over and what are the half-lives of these RNAs? We developed two assays to determine miRNA half-lives, one based on an ex vivo Dicer conditional system and a 4-thiouridine metabolic labeling pulse-chase assay. Both of these assays will be useful for globally determining miRNA half-lives in mammalian cells