Screening for modifier genes of polyglutamine-induced neuronal dysfunction using a Drosophila polyglutamine disease model.

多聚谷氨酰胺(PolyQ)疾病是一组遗传性神经退行性疾病，包括亨廷顿病和脊髓小脑性共济失调，这些疾病是由每个无关致病蛋白中多聚Q伸展的异常扩张引起的。最近有研究表明，PolyQ病患者的神经学表型是由可逆性神经元功能障碍而不是神经细胞死亡引起的。然而，到目前为止，多聚Q诱导的神经元功能障碍的分子机制还不完全清楚。为了研究多聚Q诱导的神经元功能障碍的分子机制，我们在果蝇多Q病模型中筛选了过早死亡的修饰基因，这是由神经元功能障碍引起的一种表型。我们利用GeneSwitch系统建立了一个GS-PolyQ飞系，它以RU486依赖的方式在神经系统有条件地表达一个扩展的多Q蛋白。然后，我们将这个GS-PolyQ果蝇品系与各种染色体部分缺失的突变果蝇品系(布卢明顿缺乏症试剂盒，220个品系)进行杂交，并评估它们后代的存活率。我们成功地鉴定了11个抑制系，其后代的存活率比GS-PolyQ系高。重要的是，这11个株系中有9个没有抑制多聚Q诱导的神经细胞死亡，这表明这些缺失区域包含与多聚Q诱导的神经元功能障碍有关的基因，但不包含神经细胞死亡。我们接下来在这11个缺失的染色体区域中筛选与提高存活率有关的基因，并选择了三个候选基因。我们利用RNAi进一步评估了这些候选基因的敲除效果，并确定了一个新的基因(Sup5)，它与多聚Q诱导的神经元功能障碍有关。因此，我们认为Sup5基因参与了多聚Q诱导的可逆性神经元功能障碍的新机制，为治疗多Q疾病提供了新的靶点。

The polyglutamine (polyQ) diseases are a group of inherited neurodegenerative diseases, including Huntington's disease and spinocerebellar ataxias, which are caused by an abnormal expansion of the polyQ stretch in each unrelated disease-causing protein. It has been recently suggested that the neurological phenotypes of polyQ disease patients are caused by reversible neuronal dysfunction rather than neuronal cell death. However, the molecular mechanisms involved in polyQ-induced neuronal dysfunction are not fully understood so far. To investigate the molecular mechanisms of polyQ-induced neuronal dysfunction, we screened for modifier genes of premature death in a Drosophila polyQ disease model, which is a phenotype caused by neuronal dysfunction. We established a GS-polyQ fly line which conditionally expresses an expanded polyQ protein in the nervous system in an RU486-dependent manner using the GeneSwitch system. We then crossed this GS-polyQ fly line with various mutant fly lines which have a partial deletion in their chromosomes (Bloomington deficiency kit,220 lines), and evaluated the survival rate of their offspring. We successfully identified 11 suppressor lines, whose offspring exhibited an improved survival rate compared with the GS-polyQ line. Importantly, nine of these 11 lines did not suppress polyQ-induced neuronal cell death, suggesting that these deleted regions contain genes involved in polyQ-induced neuronal dysfunction but not neuronal cell death. We next screened for genes responsible for the improved survival rate within these 11 deleted chromosomal regions, and selected three candidate genes. We further evaluated the effects of knockdown of these candidate genes using RNAi, and identified a novel gene (Sup5) which is involved in polyQ-induced neuronal dysfunction. We therefore conclude that the Sup5 gene is involved in a novel mechanism of polyQ-induced reversible neuronal dysfunction, providing a novel therapeutic target for the polyQ diseases.