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The Journal of Neuroscience, August 30, 2006, 26(35):8943-8954; doi:10.1523/JNEUROSCI.4998-05.2006

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Neurobiology of Disease
Mutations in the K⁺/Cl^– Cotransporter Gene kazachoc (kcc) Increase Seizure Susceptibility in Drosophila

Daria S. Hekmat-Scafe,^1,2 Miriam Y. Lundy,¹ Rakhee Ranga,³ and Mark A. Tanouye^1,2

¹Department of Environmental Science, Policy and Management, Division of Insect Biology, ²Department of Molecular and Cell Biology, Division of Neurobiology, and ³Division of Genetics and Development, University of California, Berkeley, California 94720

Correspondence should be addressed to Daria S. Hekmat-Scafe, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720. Email: daria{at}nature.berkeley.edu

During a critical period in the developing mammalian brain, there is a major switch in the nature of GABAergic transmission from depolarizing and excitatory, the pattern of the neonatal brain, to hyperpolarizing and inhibitory, the pattern of the mature brain. This switch is believed to play a major role in determining neuronal connectivity via activity-dependent mechanisms. The GABAergic developmental switch may also be particularly vulnerable to dysfunction leading to seizure disorders. The developmental GABA switch is mediated primarily by KCC2, a neuronal K⁺/Cl^– cotransporter that determines the intracellular concentration of Cl^– and, hence, the reversal potential for GABA. Here, we report that kazachoc (kcc) mutations that reduce the level of the sole K⁺/Cl^– cotransporter in the fruitfly Drosophila melanogaster render flies susceptible to epileptic-like seizures. Drosophila kcc protein is widely expressed in brain neuropil, and its level rises with developmental age. Young kcc mutant flies with low kcc levels display behavioral seizures and demonstrate a reduced threshold for seizures induced by electroconvulsive shock. The kcc mutation enhances a series of other Drosophila epilepsy mutations indicating functional interactions leading to seizure disorder. Both genetic and pharmacological experiments suggest that the increased seizure susceptibility of kcc flies occurs via excitatory GABAergic signaling. The kcc mutants provide an excellent model system in which to investigate how modulation of GABAergic signaling influences neuronal excitability and epileptogenesis.

Key words: seizure; epilepsy; K⁺/Cl^– cotransporter; GABA_A receptor; genetics; Drosophila

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Received Nov. 23, 2005; revised July 21, 2006; accepted July 27, 2006.

Correspondence should be addressed to Daria S. Hekmat-Scafe, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720. Email: daria{at}nature.berkeley.edu

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