Yvon Trottier 1 Introduction

Polyglutamine (polygln) expansion in specific proteins is one of the most intriguing pathogenic mechanisms causing adult-onset neurodegenerative disorders. In all the cases studied so far, the normal gene products tolerate a rather wide variation in size of a polygln tract (ranging typically between 10-35 glns) without any detectable adverse effect. However, beyond the threshold of about 35-42 glns those proteins acquire toxic properties, which correlate with a conformational change—revealed by the 1C2 antibody interaction—and a tendency of mutant proteins to aggregate in vitro and in vivo. To date nine polygln expansion disorders have been characterized, the list of which includes Huntington's disease (HD) the most frequent of them, six spinocerebellar ataxias (SCA1-3, SCA6, SCA7, and SCA17), spino-bulbar muscular atrophy (SBMA) and dentatorubral-pallidoluysian atrophy (DRPLA) (reviewed in refs. 1,2). Most of theses diseases present a strong inverse correlation between the length of the polygln tract and the age of onset of clinical symptoms. At the DNA level, the expanded CAG repeats, which code for the polygln stretch, are found to be unstable upon transmission from one generation to the other, with a clear tendency to expansion. These two features account for the anticipation phenomenon (increased severity and earlier onset of the disease in successive generations) that is observed at various degrees in polygln expansion diseases. Because anticipation is observed in many other neurological disorders (and suggested in some non-neurological diseases), for which the causative gene has not yet been cloned, it is suggested that polygln expansion could be involved in the disease process (3,4).

We reported in 1995 that an anti-polygln monoclonal antibody (Mab), 1C2, selectively recognizes polygln expansion (5). On Western blot (WB) analysis, the antibody was able to detect mutant proteins involved in HD, SCA1, and SCA3, but not the corresponding normal forms. Moreover we showed that the ability of 1C2 to detect the mutant HD protein, huntingtin, clearly increases with the polygln size: signal intensity increases by about 20-40 fold from mutant proteins with small pathological expansion (39-40 glns) to those with long expansion (60-85 glns) associated with juvenile onset (5). Thus, the efficiency of detection of pathological alleles appears to parallel the severity of the disease.

From: Methods in Molecular Biology, vol. 217: Neurogenetics: Methods and Protocols Edited by: N. T. Potter © Humana Press Inc., Totowa, NJ

Given its properties, we used the 1C2 antibody as a tool to identify new polygln expansion proteins in lymphoblastoid cell lines (LCL) derived from SCA2 and SCA7 patients (5,6). Very recently, Nakamura et al. (2) have used the 1C2 antibody to show that polygln expansion in the TATA-binding protein (TBP) is responsible for SCA17. Other groups showed that 1C2 detects an unknown protein with a long polygln stretch in some patients with childhood onset schizophrenia (7,8). In this report, we summarize the binding properties of 1C2 antibody, and outline a strategy using this antibody as a probe to detect new polygln expansion in neurodegenerative disorders, with proven or suggested anticipation.

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