Objective: To generate and characterize a Drosophila Model of KCNS2 associated Essential Tremor (ET).
Background: ET is one of the most common neurological diseases, with an estimated 7 million affected individuals in the US. The most characteristic clinical feature of ET is a kinetic tremor in the hands or arms. As the disease progresses, tremor becomes more severe and more anatomically widespread (e.g., head, trunk). Recently, we identified a mutation (p.Asp379Glu) located in the pore domain of a potassium channel alpha subunit, KCNS2, in an early onset family with autosomal dominant ET. KCNS2 is highly and selectively expressed in the brain and modulates the activity of the KV2.1 (Shab) and KV2.2 (Shab related) channels.
Methods: The pBID-UAS Drosophila vector (McCabe lab) was used to express human normal KCNS2 and mutant KCNS2 in Drosophila. Transgenic flies were crossed to a number of well-characterized lines that express and drive expression in tissue- and cell-type-specific patterns (e.g. panneuronally or motor neurons). To determine the effects of human wildtype and mutant KCNS2 on adult clock neuron activity, electrophysiology recordings were performed by using whole cell voltage-clamp. Using a Shab specific toxin we were able to isolate the Shab current which is a voltage-senstive non-inactivating potassium current. Expression of human wildtype KCNS2 caused the Shab current to become an inactivating current activating at more hyperpolarised currents. Expression of human mutant KCNS2 caused both phenotypes but to a greater extent. In addition to neuronal degeneration we also investigated the behavioral manifestations of nervous system dysfunction in the transgenic flies.
Results: Here we express human normal and mutant (p.Asp379Glu) forms of KCNS2 in Drosophila (panneuronally and restricted to subsets of neurons) and produce adult onset leg shaking, abdomen pulsations and shuddering under ether anesthetization in addition to bilateral wing elevation indicative of loss of neurons during aging. Electrophysiological recordings show expression of human KCNS2 (particularly the mutant form) switched Shab into an inactivating current which would be expected to contribute to neuronal hyperexcitability.
Conclusion: Our Drosophila model recapitulates some of the features of ET, and can now be used to advance our understanding of disease pathogenesis and to identify pathways that can be targeted for pharmaco-therapeutics for ET.