Mettl14 Is Essential for Epitranscriptomic Regulation of Striatal Function and Learning

N6-methyladenosine (m6A) regulates mRNA metabolism and translation, serving as an important source of post-transcriptional regulation. To date, the functional consequences of m6A deficiency within the adult brain have not been determined. To achieve m6A deficiency, we deleted Mettl14, an essential component of the m6A methyltransferase complex, in two related yet discrete mouse neuronal populations: striatonigral and striatopallidal. Mettl14 deletion reduced striatal m6A levels without altering cell numbers or morphology. Transcriptome-wide profiling of m6A-modified mRNAs in Mettl14-deleted striatum revealed downregulation of similar striatal mRNAs encoding neuron- and synapse-specific proteins in both neuronal types, but striatonigral and striatopallidal identity genes were uniquely downregulated in each respective manipulation. Upregulated mRNA species encoded non-neuron-specific proteins. These changes increased neuronal excitability, reduced spike frequency adaptation, and profoundly impaired striatal-mediated behaviors. Using viral-mediated, neuron-specific striatal Mettl14 deletion in adult mice, we further confirmed the significance of m6A in maintaining normal striatal function in the adult mouse. •Mettl14 is required for m6A mRNA methylation in the adult mammalian brain•m6A deficiency in both D1 and D2 striatal neurons downregulates neuronal mRNAs•m6A deficiency in striatal neurons impairs learning and performance•Striatal m6A deficiency alters firing properties without morphological changes Koranda et al. demonstrate Mettl14 is indispensable for m6A mRNA methylation in the adult mammalian brain. Striatal Mettl14 deficiency decreases m6A tagging, altering the epitranscriptome profile. Mettl14 deficiency impairs behavior and alters intrinsic neuronal firing in the absence of morphological changes.