Gain-of-function mutations in the UNC-2/CaV2α channel lead to hyperactivity and excitation-dominant synaptic transmission in Caenorhabditis elegans

Mutations in pre-synaptic voltage gated calcium channels can lead to familial hemiplegic migraine type 1 (FHM1). While mammalian studies indicate that the migraine brain is hyperexcitable due to enhanced excitation or reduced inhibition, the molecular and cellular mechanisms underlying this excitatory/inhibitory (E/I) imbalance are poorly understood. We identified a gain-of-function (gf) mutation in the Caenorhabditis elegans CaV2 channel 1 subunit, UNC-2, which leads to increased calcium currents. unc-2(gf) mutants exhibit hyperactivity and seizure-like motor behaviors. Expression of the unc-2 gene with FHM1 substitutions R192Q and S218L leads to hyperactivity similar to that of unc-2(gf) mutants unc-2(gf) mutants display increased cholinergic- and decreased GABAergic-transmission. Moreover, we reveal that and increased cholinergic transmission in unc-2(gf) mutants leads to reduction of GABA synapses in a TAX-6/calcineurin dependent manner. Our studies provide mechanistic insight into how CaV2 gain-of-function mutations disrupt excitation-inhibition balance in the nervous system.