Ataxin-7 expression analysis in controls and spinocerebellar ataxia type 7 patients

Abstract

Expansion of polymorphic CAG repeats encoding polyglutamine cause at least eight inherited neurodegenerative diseases, including Huntington disease and the spinocerebellar ataxias. However, the pathways by which proteins containing expanded polyglutamine tracts cause disease remain unclear. To gain insight into the function of the SCA7 gene product, ataxin-7, as well as its contribution to cell death in spinocerebellar ataxia type 7 (SCA7), polyclonal antibodies were generated and ataxin-7 expression was examined within neuronal tissues from controls and three SCA7 patients. Immunoblotting demonstrates that ataxin-7 is widely expressed but that expression levels vary between tissues. Immunohistochemical analyses indicate that ataxin-7 is expressed within neurons both affected and unaffected in SCA7 pathology and that subcellular localization varies depending upon the neuronal subtype. Additionally, ataxin-7 staining was detected throughout control retina, including intense staining within the cell bodies and photosensitive outer segments of cone photoreceptors. Anti-ataxin-7 antibodies revealed intranuclear inclusions within surviving inferior olivary and cortical pyramidal neurons, as well as within surviving photoreceptor and ganglion cells of SCA7 patients harboring either 42 or 66 CAG repeats at the SCA7 locus. In contrast, inclusion formation was not detected within neurons of a patient with 41 repeats. This study broadens the current understanding of ataxin-7 localization and incorporates for the first time analysis of late-onset SCA7 patients where polyglutamine tract lengths are relatively shorter and disease course less severe than in previously described infantile-onset cases.