We tested whether proteins implicated in Huntington's and other polyglutamine (polyQ) expansion diseases can cause axonal transport defects. Reduction of Drosophila huntingtin and expression of proteins containing pathogenic polyQ repeats disrupt axonal transport. Pathogenic polyQ proteins accumulate in axonal and nuclear inclusions, titrate soluble motor proteins, and cause neuronal apoptosis and organismal death. Expression of a cytoplasmic polyQ repeat protein causes adult retinal degeneration, axonal blockages in larval neurons, and larval lethality, but not neuronal apoptosis or nuclear inclusions. A nuclear polyQ repeat protein induces neuronal apoptosis and larval lethality but no axonal blockages. We suggest that pathogenic polyQ proteins cause neuronal dysfunction and organismal death by two non-mutually exclusive mechanisms. One mechanism requires nuclear accumulation and induces apoptosis; the other interferes with axonal transport. Thus, disruption of axonal transport by pathogenic polyQ proteins could contribute to early neuropathology in Huntington's and other polyQ expansion diseases.

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Abstract. Microtubules and microtubule-associated proteins (MAPs) have been isolated from cultured cells of Drosophila melanogaster by a taxol-dependent polymerization procedure. The principal MAPs are a group of four polypeptides with similar electrophoretic mobilities corresponding to -Mr 205,000 (the 205K MAP). These proteins are resistant to precipitation by boiling. One mouse monoclonal antibody and one polyclonal rabbit antiserum specific for the Mr 205,000 MAP were produced and characterized by immunoblotting and indirect immunofluorescence. Both antibody preparations stain the Mr 205,000 molecules and an Mr 255,000 molecule in immunoblots of Drosophila cell homogenates; the rabbit antiserum also stains an Mr 150,000 triplet. Both preparations stain the microtubules of the mitotic spindle, and the rabbit antiserum stains the cytoplasmic microtubules as well. Experiments using affinity-purified rabbit antiserum demonstrate that it is the Mr 205,000 species that is located in the mitotic apparatus and on cytoplasmic microtubules. A random shear genomic library was produced in the expressing vector lambda gtl 1 and screened with the rabbit antiserum to isolate the DNA sequences encoding these polypeptides. Several cross-hybridizing clones were recovered, shown to encode antigenic determinants in the Mr 205,000 MAP, and characterized by hybridization to Northern blots of mRNA and Southern blots of genomic DNA. Analysis by in situ hybridization reveals that the gene encoding the 205K MAP is located in polytene region 100EF.