Abstract:
The Slc25a46 gene is a member of the SLC25 (solute carrier family 25) family, which consists of mitochondrial carrier proteins. Its function is totally unknown and neither functional mutations nor correlations with disease pathogenesis in animal organisms have been reported so far. Most of the SLC25 members are located in the inner mitochondrial membrane and transport specific substrates inside and outside of the mitochondrial matrix. Several diseases are caused by the mutations in the mitochondrial carrier proteins that affect either directly oxidative phosphorylation or metabolism. Dr. Eleni Douni’s research group has recently created, through random mutagenesis using N-ethyl-N nitrosouria (ENU), a new mouse model of recessive autosomal neurological disease characterized by ataxia and epilepsy that is caused by a nonsense point mutation in the Slc25a46 gene. Our previous studies showed that this mutation replaced a C (cytosine) by a T (thymine) in the coding region of the Slc25a46 gene introducing a premature stop cordon. As a result, the truncated protein has only 95 amino acids instead of the 418 amino acids displayed by the SLC25A46 wild type protein, which has mitochondrial localization. Although this mutation does not affect the expression of Slc25a46 at the mRNA level, the 46kDa SLC25A46 wild type protein is not produced in ataxic mice.
The aim of the present study was the creation and characterization of human Slc25a46 transgenic mice (TgSlc25a46) in order to genetically confirm that the mutation in the Slc25a46 gene is responsible for the ataxic phenotype through genetic replacement experiments. In this work, the expression of the Slc25a46 transgene was studied at the mRNA and the protein levels in different tissues among two TgSlc25a46 lines, the phenotype of the transgenic mice was analysed and crosses were established for the rescue of the ataxic phenotype in the presence of the human Slc25a46 transgene. Our results showed that 1) the human Slc25a46 transgene follows the expression pattern of the endogenous Slc25a46 gene which is mainly expressed in the tissues of the Central Nerve System such as brain, cerebellum, and spinal cord, both at the mRNA and protein levels, 2) the expression of the Slc25a46 transgene depends on its copy number, 3) the transgenic mice carrying the nonsense mutation (TgSlc25a46 m/m) rescued the ataxic phenotype and displayed a physiological expression pattern of the human SLC25A46 protein, and 4) the mutation in the Slc25a46 gene is indeed responsible for the ataxic phenotype (genetical confirmation for the mutation). Further studies on the Slc25a46 gene’s function will reveal the molecular mechanism involved in disease pathogenesis dispayed by the ataxic model and identify possibly novel metabolic pathways where mitochondria play important role.
