Connexin 47 (Cx47)-Deficient Mice with Enhanced Green Fluorescent Protein Reporter Gene Reveal Predominant Oligodendrocytic Expression of Cx47 and Display Vacuolized Myelin in the CNS

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Abstract
To further characterize the recently described gap junction gene connexin 47 (Cx47), we generated Cx47-null mice by replacing the Cx47 coding DNA with an enhanced green fluorescent protein (EGFP) reporter gene, which was thus placed under control of the endogenous Cx47 promoter. Homozygous mutant mice were fertile and showed no obvious morphological or behavioral abnormalities. Colocalization of EGFP fluorescence and immunofluorescence of cell marker proteins revealed that Cx47 was mainly expressed in oligodendrocytes in highly myelinated CNS tissues and in few calcium-binding protein S100β subunit-positive cells but not in neurons or peripheral sciatic nerve. This corrects our previous conclusion that Cx47 mRNA is expressed in brain and spinal cord neurons (Teubner et al., 2001). Cx47 protein was detected by Western blot analysis after immunoprecipitation in CNS tissues of wild-type mice but not in heart or Cx47-deficient tissues. Electron microscopic analysis of CNS white matter in Cx47-deficient mice revealed a conspicuous vacuolation of nerve fibers, particularly at the site of the optic nerve where axons are first contacted by oligodendrocytes and myelination starts. Initial analyses of Cx32/Cx47-double-deficient mice showed that these mice developed an action tremor and died on average at 51 d after birth. The central white matter of these double-deficient mice exhibited much more abundant vacuolation in nerve fibers than mice deficient only in Cx47.