Abstract
Animals adapt to environmental challenges with long-term changes at the behavioral, circuit, cellular, and synaptic levels which often require new protein synthesis. The discovery of reversible N6-methyladenosine (m6A) modifications of mRNA has revealed an important layer of post-transcriptional regulation which affects almost every phase of mRNA metabolism and therefore translational control. Many in vitro and in vivo studies have demonstrated the significant role of m6A in cell differentiation and survival, but its role in adult neurons is understudied. We used cell-type specific gene deletion of Mettl14, which encodes one of the subunits of the m6A methyltransferase, and Ythdf1, which encodes one of the cytoplasmic m6A reader proteins, in dopamine D1 receptor expressing or D2 receptor expressing neurons. Mettl14 or Ythdf1 deficiency blunted responses to environmental challenges at the behavioral, cellular, and molecular levels. In three different behavioral paradigms, gene deletion of either Mettl14 or Ythdf1 in D1 neurons impaired D1-dependent learning, whereas gene deletion of either Mettl14 or Ythdf1 in D2 neurons impaired D2-dependent learning. At the cellular level, modulation of D1 and D2 neuron firing in response to changes in environments was blunted in all three behavioral paradigms in mutant mice. Ythdf1 deletion resembled impairment caused by Mettl14 deletion in a cell type-specific manner, suggesting YTHDF1 is the main mediator of the functional consequences of m6A mRNA methylation in the striatum. At the molecular level, while striatal neurons in control mice responded to elevated cAMP by increasing de novo protein synthesis, striatal neurons in Ythdf1 knockout mice didn't. Finally, boosting dopamine release by cocaine drastically increased YTHDF1 binding to many mRNA targets in the striatum, especially those that encode structural proteins, suggesting the initiation of long-term neuronal and/or synaptic structural changes. While the m6A-YTHDF1 pathway has similar functional significance at cellular level, its cell type specific deficiency in D1 and D2 neurons often resulted in contrasting behavioral phenotypes, allowing us to cleanly dissociate the opposing yet cooperative roles of D1 and D2 neurons.