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The Journal of Neuroscience, March 11, 2009, 29(10):3103-3108; doi:10.1523/JNEUROSCI.4868-08.2009

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Brief Communications
The Septate Junction Protein Caspr Is Required for Structural Support and Retention of KCNQ4 at Calyceal Synapses of Vestibular Hair Cells

Aurea D. Sousa,¹ Leonardo R. Andrade,^1,2 Felipe T. Salles,¹ Anilkumar M. Pillai,³ Elizabeth D. Buttermore,³ Manzoor A. Bhat,³ and Bechara Kachar¹

¹Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders–National Institutes of Health, Bethesda, Maryland 20892-8027, ²Institute of Biomedical Science, Center of Health Sciences, Federal University of Rio de Janeiro, 21941-590, Rio de Janeiro, Rio de Janeiro, Brazil, and ³Department of Cell and Molecular Physiology, Curriculum in Neurobiology, Neurodevelopmental Disorders Research Center, University of North Carolina–Neuroscience Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7545

Correspondence should be addressed to Dr. Bechara Kachar, Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders–National Institutes of Health, Building 50, Room 4249, 50 South Drive, Bethesda, MD 20892-8027. Email: kacharb{at}nidcd.nih.gov

The afferent innervation contacting the type I hair cells of the vestibular sensory epithelia form distinct calyceal synapses. The apposed presynaptic and postsynaptic membranes at this large area of synaptic contact are kept at a remarkably regular distance. Here, we show by freeze-fracture electron microscopy that a patterned alignment of proteins at the calyceal membrane resembles a type of intercellular junction that is rare in vertebrates, the septate junction (SJ). We found that a core molecular component of SJs, Caspr, colocalizes with the K⁺ channel KCNQ4 at the postsynaptic membranes of these calyceal synapses. Immunolabeling and ultrastructural analyses of Caspr knock-out mice reveal that, in the absence of Caspr, the separation between the membranes of the hair cells and the afferent neurons is conspicuously irregular and often increased by an order of magnitude. In these mutants, KCNQ4 fails to cluster at the postsynaptic membrane and appears diffused along the entire calyceal membrane. Our results indicate that a septate-like junction provides structural support to calyceal synaptic contact with the vestibular hair cell and that Caspr is required for the recruitment or retention of KCNQ4 at these synapses.

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Received Oct. 9, 2008; revised Jan. 9, 2009; accepted Feb. 2, 2009.

Correspondence should be addressed to Dr. Bechara Kachar, Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders–National Institutes of Health, Building 50, Room 4249, 50 South Drive, Bethesda, MD 20892-8027. Email: kacharb{at}nidcd.nih.gov

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