Identification and localization of ataxin-7 in brain and retina of a patient with cerebellar ataxia type II using anti-peptide antibody

Autosomal dominant cerebellar ataxias (ADCAs) are a complex group of neurod egenerative disorders characterized by progressive degeneration of the cere bellum, brain stem and spinal cord, The spinocerebellar ataxia type 7 (SCA7 ) is associated with pigmentary macular dystrophy and retinal degeneration leading to blindness caused by a CAG/polyglutamine (polyGln) expansion in t he coding region of the SCA7 gene/protein, The SCA7 gene codes for ataxin-7 , a protein of unknown function. To investigate its cellular and subcellula r localization, we have developed a sequence-specific polyclonal antibody a gainst the N-terminal part of the protein, Immunohistochemical analysis ind icated that ataxin-7 accumulates as single nuclear inclusion (NI) in the ce lls of the brain and retina of a SCA7 patient but not of controls, The 1C2 antibody, directed against expanded polyGln, confirmed the aggregation of m utant ataxin-7 in these NIs. Furthermore, ubiquitin was found in these aggr egates, suggesting that mutant ataxin-7 is a target for ubiquitin-dependent proteolysis, but resistant to removal. Electron microscopic studies using immunogold labeling showed that ataxin-7 immunoreactive NIs appear as dense aggregates containing a mixture of granular and filamentary structures. To gether, these data confirm the presence of Ms in brain and retina of a SCA7 patient, a common characteristic of disorders caused by expanded CAG/polyG ln repeats, (C) 1999 Elsevier Science B.V. All rights reserved.