Molecular Logic of Synaptic Diversity Between Tonic and Phasic Motoneurons.

Although neuronal subtypes display unique synaptic organization and function, the underlying transcriptional differences that establish these features is poorly understood. To identify molecular pathways that contribute to synaptic diversity, single neuron PatchSeq RNA profiling was performed on tonic and phasic glutamatergic motoneurons. Tonic motoneurons form weaker facilitating synapses onto single muscles, while phasic motoneurons form stronger depressing synapses onto multiple muscles. Super-resolution microscopy and imaging demonstrated synaptic active zones in phasic motoneurons are more compact and display enhanced Ca influx compared to their tonic counterparts. Genetic analysis identified unique synaptic properties that mapped onto gene expression differences for several cellular pathways, including distinct signaling ligands, post-translational modifications and intracellular Ca buffers. These findings provide insights into how unique transcriptomes drive functional and morphological differences between neuronal subtypes.