Combinatorial transcriptional regulation establishes subtype-appropriate synaptic properties in auditory neurons.

Neurons develop diverse synapses that vary in content, morphology, and size. Although transcriptional regulators of neurotransmitter identity are known, it remains unclear how synaptic features are patterned among neuronal subtypes. In the auditory system, glutamatergic synaptic properties vary across three spiral ganglion neuron (SGN) subtypes that collectively encode sound. Here, we demonstrate that Maf transcription factors combinatorially shape synaptic properties in SGNs. SGN subtypes express different ratios of c-Maf and Mafb, which act redundantly to impart subtype identities and individually to shape subtype-appropriate gene expression programs. On their own, c-Maf and Mafb have independent and opposing effects on synaptic features and hearing. A mutation in the MAFB leucine zipper domain causes deafness in humans, underscoring the importance of regulated Maf activity for hearing. Thus, functional diversity and coordinated action of Maf family members enable flexible and robust control of gene expression needed to generate synaptic heterogeneity across neuronal subtypes.