BK channel gain-of-function disrupts limb control by suppressing neurotransmission during a critical developmental window

Gain-of-function mutations in BK potassium channels (BK GOF) cause debilitating involuntary limb movements. BK channels modulate action potential shape and neurotransmission in mature neurons, yet some BK GOF mutations also cause neurodevelopmental morbidities. Thus, whether BK GOF impairs limb control by altering the excitation/inhibition of mature motor circuits, or by disrupting their development, remains unclear. To address this issue, we developed a genetic method enabling spatiotemporal control of BK channel expression in neurons of the fruit fly, Drosophila. In concert with high-resolution measurements of limb kinematics, we demonstrate that GOF BK channels act during a narrow neurodevelopmental period to perturb limb control in adult flies. During this period, BK GOF alters synaptic localisation of the key active zone protein Bruchpilot and suppresses excitatory neurotransmission. In a wild-type background, we find that reducing neural activity during neurodevelopment yields similar motor defects to those observed in BK GOF flies. Conversely, enhancing neural excitability during development rescues alterations in limb kinematics in BK GOF flies. Collectively, our results suggest that BK GOF perturbs limb control largely by disrupting activity-dependent aspects of neuronal development.