Immunohistochemical study of neuronal intranuclear and cytoplasmic inclusions in Machado-Joseph disease

Machado-Joseph disease (MJD) is a dominantly inherited spinocerebellar disorder, and expansions of trinucleotide (CAG) at chromosome 14 have been shown to be the locus of this disorder. Polyglutamine CAG stretches in the neuronal cytoplasms and nuclei were studied with immunolabeling using 1C2, a monoclonal antibody recognizing polyglutamine stretches, and polyclonal antiubiquitin antibody in six genetically verified cases of MJD. 1C2 clearly labeled two types of neuronal intranuclear inclusions (NII) and neuronal cytoplasmic inclusions (NCI) in the substantia nigra, pontine nucleus, dentate nucleus and spinal anterior horn where NII and NCI were also positive for ubiquitin, as were extracellular dot-like structures and oligodendroglial inclusions. 1C2-positive NII and NCI had a lesion-specific distribution. While the spinal motoneurons contained only 1C2-positive NCI and lacked 1C2-positive NII, the ventral pontine nucleus neurons had many 1C2-positive NII and few 1C2-positive NCI. Semi-quantitative examination of NII and NCI positive for 1C2 or ubiquitin demonstrated that there were more 1C2-positive NII and NCI than ubiquitin-positive ones. It is noteworthy that the nuclei of the spinal motoneurons lacked 1C2-positive immunoreactivity, so that ubiquitination of 1C2-positive structures is presumed to occur late in the course of the disease.