Elucidation of molecular mechanisms of spinocerebellar degeneration through positional cloning of causative genes and development of the animal models.

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To elucidate molecular mechanisms of neuronal degeneration in hereditary spinocerebellar ataxia, and to develop therapeutic measures for these diseases, we have attempted to create animal models for dentatorubral-pallidoluysian atrophy (DRPLA), a form of hereditary spinocerebellar degenerations . As the first step, we have isolated and determined the detailed structures of full length human and mouse cDNA clones for DRPLA .Furthermore, we have also isolated human and mouse genomic DNA for DRPLA . We have revealed that the DRPLA gene is widely expressed not only in the central nervous system but also in the somatic organs . We have found that there is a considerable somatic mosaicism of the expanded CAG repeats in the central nervous system of DRPLA patients, suggesting the somatic instability of the expanded CAG repeats . To create animal models, we have undertaken two strategies . As one strategy, we have cloned a genomic clone from a DRPLA patient with the longest (78 repeat) CAG repeat, which was inserted into embryonic stem cells (ES cells) with a selectable marker . ES cells containing single copy of mutant DRPLA gene were selected and chimeric mice was obtained . Germline transmission is being attempted now . As another strategy, we have created mutant human DRPLA cDNA carrying the expanded CAG repeat . Transgenic mouse carrying multiple copies of the mutant DRPLA cDNA were made, and the phenotype is being investigated . These two lines of animal models should be highly useful for the future study of the molecular mechanisms of DRPLA,and to develop therapeutic measure for DRPLA .