Analysis of the roles of POMGnT1 in development and maintenance of certral nervous system and skeletal muscle

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Protein O-linked mannose β1, 2-N-acetylglucosaminyltransferase 1(POMGnT1) is an enzyme that transfers N-acetylglucosamine to O-mannose of glycoproteins, and is indispensable for (O-mannosyl glycosylation of alpha-dystroglycan(α-DG), a component of the dystrophin-glycoprotein complex. Mutation of the POMGnT1 gene is a cause of muscle-eye-brain(MEB) disease, which is characterized by severe congenital muscular dystrophy and abnormalities of the eyes and central nervous system(CNS). To obtain a better understanding of the pathogenesis of MEB disease, we mutated the POMGnT1 gene in mice using a targeting technique.1) Skeletal muscle The mutant muscle showed aberrant glycosylation of α-DG and α-DG from mutant muscle failed to bind laminin in a binding assay. POMGnT1^<-/-> muscle showed minimal pathological changes with very low serum creatinine kinase levels, and had normally formed muscle basal lamina. Importantly, POMGnT1^<-/-> satellite cells proliferated slowly, but efficiently differen … More tiated into multinuclear myotubes in vitro. Transfer of a retrovirus vector-mediated POMGnT1 gene into POMGnT1^<-/-> myoblasts completely restored the glycosylation of α-DG, but proliferation of the cells was not improved. Our results suggest that α-DG is not directly involved in the proliferation and differentiation of myoblasts but that its glycosylation is important for maintenance of the proliferative capacity of satellite cells in the postnatal stage.2) CNS The cerebral cortex of POMGnT1^<-/-> mice showed abnormal migration of neurons, disrupted glia limitans and reactive gliosis. The expression of reelin was widely up-regulated in the mutant neocortex. We tested whether the restoration of POMGnT1 expression in neuron results in normal migration along the radial glia. To this end, we electroporated a POMGnT1-expressing plasmid into the ventricular zone of E12 and E15 embryos in utero.Surprisingly, the migration pattern of POMGnT1-deficient neuron did not change after restoration of POMGnT1 expression. The results suggest that the abnormal migration of POMGnT1^<-/-> neurons is not due to deficiency ogf POMGn1 activity in neuron but likely due to abnormality of radial glial cells(Bergmann glia), which have long radial processes extending from the ventricular zone(VZ) to the pial surface and serve a railroad of neuronal migration. Less