The long term objectives of the research program are to understand protein structure/function relationships in retinal photoreceptors, and to translate this understanding to the treatment of patients with retinitis pigmentosa and related disorders. In humans, CNGB1 gene defects cause hereditary retinal degeneration. We have therefore focused on the murine Cngbl locus that expresses, exclusively in the rod outer segment (ROS), two relatively abundant proteins: plasma membrane localized 2-subunit of the cGMP-gated cation channel and cytoplasmic glutamic acid-proline rich polypeptide (GARP-2). The rod cGMP-gated cation channel plays a critical role in vision by regulating the flow of calcium and sodium ions into the rod cell. In addition, both the 2-subunit and GARP-2 interact with peripherin-2/rds, a disk membrane protein, and thus may play essential structural roles. To determine the contribution of the proteins in ROS, we generated a homozygous Cngbl photoreceptor null (5'KO), and are analyzing the mice using light and EM level analysis, ERG and single cell recordings, and Western analysis. Homozygous 5'KO mice show a significant reduction (>30 fold) in light sensitivity and attenuated b-wave response, but are functional prior to the onset of retinal degeneration. Surprisingly, in the 59 KO not only is the 2-subunit absent but the channel 1-subunit is also greatly reduced in abundance in ROS. We hypothesize that the GARP region has an important structural role in the photoreceptor and that GARP-2, like the 2-subunit has also an important functional role. We will directly examine the structural and functional roles of the GARP region of the beta subunit and of GARP-2 by targeted deletion of GARP-2 expression and introduction of transgenes into 59 KO and 2-subunit knockout mice (39 KO). The proposed studies will help to establish the function of the Cngbl encoded GARP region and of GARP-2 in the photoreceptor, and hence provide important insights into the mechanisms whereby CNGB1 gene defects cause hereditary retinal degeneration. The studies may also yield new targets for intervention as possible treatments for certain forms of hereditary retina degeneration.
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