Study of the deafness gene Grxcr1 and a paralog, Grxcr2

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DESCRIPTION (provided by applicant): Recessive mutations at the mouse pirouette (pi) locus cause sensorineural deafness and vestibular dysfunction due to defective maturation of sensory hair cells in the inner ear. We have recently identified the genetic basis of these pathologies as null mutations in a novel gene, Grxcr1. Pathology in pirouette sensory cells suggests that this gene is required for increasing the diameter of stereocilia during early postnatal maturation of sensory cells, potentially through regulation of actin filament distribution in the stereocilia core. Grxcr1 is expressed in sensory cells of the inner ear and encodes a 290 amino acid protein containing a central domain with significant similarity to glutaredoxin proteins, and a C-terminal cysteine-rich domain. Transfection of Grxcr1 constructs into cultured cells indicates that it localizes to actin filament-rich structures at the dorsal/apical surface. In addition, the actin filament content in dorsal projections in transfected fibroblasts often appears more prominent on cells expressing GRXCR1, suggesting a local, direct role for the protein in the induction and/or stabilization of the actin cytoskeleton of these structures. Grxcr1-related genes are present in a wide range of metazoan species, including a related paralogous gene (Grxcr1) also expressed selectively in the mouse inner ear. Using molecular genetic and cell biological approaches, we propose to investigate the biochemical, cellular, and physiological roles of GRXCR1 and GRXCR2. We will determine the sub cellular localization of these proteins in inner ear tissues (Aim 1), identify domains required for activities of the proteins in vitro, in cultured cells and inner ear tissue explants, and examine the interdependence of these activities (Aim 2), identify additional proteins that may interact directly with GRXCR1 (Aim 3), and generate a targeted mutation of Grxcr2 to characterize a potential novel model of inner ear dysfunction (Aim 4). Through these aims, we will investigate potential links between stereocilia development, actin dynamics, and processes influenced by reduction/oxidation pathways, and thereby provide insight into the molecular control of sensory cell development and function.