Gephyrin (GPHN) regulates the clustering of postsynaptic components at inhibitory synapses and is involved in pathophysiology of neuropsychiatric disorders. Here, we uncover an extensive diversity of GPHN transcripts that are tightly controlled by splicing during mouse and human brain development. Proteomic analysis reveals at least a hundred isoforms of GPHN incorporated at inhibitory Glycine and gamma-aminobutyric acid A receptors containing synapses. They exhibit different localization and postsynaptic clustering properties, and altering the expression level of one isoform is sufficient to affect the number, size, and density of inhibitory synapses in cerebellar Purkinje cells. Furthermore, we discovered that splicing defects reported in neuropsychiatric disorders are carried by multiple alternative GPHN transcripts, demonstrating the need for a thorough analysis of the GPHN transcriptome in patients. Overall, we show that alternative splicing of GPHN is an important genetic variation to consider in neurological diseases and a determinant of the diversity of postsynaptic inhibitory synapses.

How does the inner ear communicate with the cerebellar cortex to maintain balance and posture?

The precise regulation of the cellular mechanisms underlying axonal morphogenesis is essential to the formation of functional neuronal networks. We previously identified the autism-candidate kinase NUAK1 as a central regulator of axon branching in mouse cortical neurons through the control of mitochondria trafficking. How does local mitochondrial position or function regulate axon branching during development? Here, we characterized the metabolic regulation in the developing axon and report a marked metabolic decorrelation between axon elongation and collateral branching. We next solved the cascade of event leading to presynaptic clustering and mitochondria recruitment during spontaneous branch formation. Interestingly and contrary to peripheral neurons, mitochondria are recruited after but not prior to branch formation in cortical neurons. Using flux metabolomics and fluorescent biosensors, we observed that NUAK1 deficiency significantly impairs mitochondrial metabolism and axonal ATP concentration. Upregulation of mitochondrial function is sufficient to rescue axonal branching in NUAK1 null neurons in vitro and in vivo. Altogether, our results indicate that NUAK1 exerts a dual function during axon branching through its ability to control mitochondria distribution and activity, and suggest that a mitochondrial-dependent remodeling of local metabolic homeostasis plays a critical role during axon morphogenesis. RESULTS Cortical axon elongation and collateral branching rely on distinct metabolic pathways

Gephyrin (GPHN) regulates the clustering of postsynaptic components at inhibitory synapses and is involved in pathophysiology of neuropsychiatric disorders. Here, we uncover an extensive diversity of GPHN transcripts that are tightly controlled by splicing during mouse and human brain development. Proteomic analysis reveals at least a hundred isoforms of GPHN incorporated at inhibitory Glycine and GABA-A receptors containing synapses. They exhibit different localization and postsynaptic clustering properties, and altering the expression level of one isoform is sufficient to affect the number, size, and density of inhibitory synapses in cerebellar Purkinje cells. Furthermore, we discovered that splicing defects reported in neuropsychiatric disorders are carried by multiple alternative GPHN transcripts, demonstrating the need for a thorough analysis of the GPHN transcriptome in patients. Overall, we show that alternative splicing of GPHN is an important genetic variation to consider in neurological diseases and a determinant of the diversity of postsynaptic inhibitory synapses.