The role of connexin32 in the pathogenesis of CMTX

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DESCRIPTION (provided by applicant): Mutations in GJB1, GJA1, and GJA12, the genes that encode human connexin32 (hCx32), hCx43, and hGx47, cause the X-linked form of Charcot-Marie-Tooth disease (CMT1X), oculodentodigital dysplasia (ODDD), and Pelizaeus-Merzbacher-like disease (PMLD), respectively, all of which cause important CNS abnormalities that appear to be related to abnormal functioning of oligodendrocytes. The central theme of this grant is that Cx30:Cx32 and Cx43:Cx47 heterotypic channels mediate astrocyte/oligodendrocyte (A/O) coupling, which is disrupted by mutations of GJB1/Cx32, GJA1/Cx43, or GJA12/Cx47. 1. Investigate the molecular defects of hCx47 mutants causing PMLD. We will characterize further the nature of these defects, and determine whether wild type (WT) hCx47 or these hCx47 mutants can form functional channels with hCx43 by dye transfer and electrophysiology. 2. Investigate the molecular defects of hCx43 mutants causing ODDD. We will investigate the molecular nature of the mutants proteins, determine whether cells expressing an ODDD mutant can form functional channels by themselves, or with cells expressing either WT hCx43 or WT hCx47, and determine whether ODDD mutants' have dominant-negative effects on-WT hCx43. 3. Determine whether hCx32 "CNS mutants" have dominant effects on hCx47. In HeLa cells these "CNS mutants" accumulate either in the endoplasmic reticulum (ER) or in the Golgi. Our preliminary evidence indicates that co-expression of these "CNS mutants" with WT hCx47 results in partial retention of Wt hCx47 in the ER or Golgi, indicating that these Cx32 mutants exert a dominant effect on WT hCx47. We will characterize further the nature of these defects. 4. Determine the role of Cx32 and Cx47 in astrocyte/oligodendrocyte coupling. We will immunostain the brains of mice that lack Cx32 and/or Cx47, and determine whether the localization of their proposed partners is altered. We will also investigate A/O coupling by injecting astrocytes genetically labeled with green fluorescent protein (GFP) in acute spinal cord slices from Gjb1/cx32 and Gja12/cx47 double null" mice with small molecules that can cross GJs. In this way, we will determine the relative importance of the two kinds of heterotypic channels in A/0 coupling.