Abstract

Mutations in hundreds of genes cause neurodevelopmental disorders with abnormal motor behavior alongside cognitive deficits. Boys with fragile X syndrome (FXS), a leading monogenic cause of intellectual disability, often display repetitive behaviors, a core feature of autism. By direct observation and manual analysis, we characterized spontaneous-motor-behavior phenotypes of Drosophila dfmr1 mutants, an established model for FXS. We recorded individual 1-day-old adult flies, with mature nervous systems and prior to the onset of aging, in small arenas. We scored behavior using open-source video-annotation software to generate continuous activity timelines, which were represented graphically and quantitatively. Young dfmr1 mutants spent excessive time grooming, with increased bout number and duration; both were rescued by transgenic wild-type dfmr1⁺. By two grooming-pattern measures, dfmr1-mutant flies showed elevated repetitions consistent with perseveration, which is common in FXS. In addition, the mutant flies display a preference for grooming posterior body structures, and an increased rate of grooming transitions from one site to another. We raise the possibility that courtship and circadian rhythm defects, previously reported for dfmr1 mutants, are complicated by excessive grooming. We also observed significantly increased grooming in CASK mutants, despite their dramatically decreased walking phenotype. The mutant flies, a model for human CASK-related neurodevelopmental disorders, displayed consistently elevated grooming indices throughout the assay, but transient locomotory activation immediately after placement in the arena. Based on published data identifying FMRP-target transcripts and functional analyses of mutations causing human genetic neurodevelopmental disorders, we propose the following proteins as candidate mediators of excessive repetitive behaviors in FXS: CaMKIIα, NMDA receptor subunits 2A and 2B, NLGN3, and SHANK3. Together, these fly-mutant phenotypes and mechanistic insights provide starting points for drug discovery to identify compounds that reduce dysfunctional repetitive behaviors.

摘要

数百个基因的突变会导致神经发育障碍，伴随着异常的运动行为和认知缺陷。患有脆性 X 综合征 (FXS) 的男孩是导致智力残疾的主要单基因原因，他们经常表现出重复行为，这是自闭症的核心特征。通过直接观察和人工分析，我们表征了果蝇 dfmr1突变体的自发运动行为表型，这是一个已建立的 FXS 模型。我们在小场地记录了个体 1 天大的成年苍蝇，它们具有成熟的神经系统并且在衰老开始之前。我们使用开源视频注释软件对行为进行评分，以生成连续的活动时间线，并以图形和定量的方式表示。年轻的dfmr1突变体花费过多的时间梳理毛发，增加回合数和持续时间；两者都被转基因野生型dfmr1 ⁺拯救。通过两种梳理模式测量，dfmr1 -突变果蝇显示出与坚持一致的重复次数增加，这在 FXS 中很常见。此外，突变果蝇表现出对修饰身体后部结构的偏好，并且从一个位置到另一个位置的修饰转换率增加。我们提出了求爱和昼夜节律缺陷的可能性，先前报道的dfmr1突变体，因过度梳理而复杂化。我们还观察到CASK 中的修饰显着增加突变体，尽管它们的行走表型显着降低。突变果蝇是人类CASK相关神经发育障碍的模型，在整个测定过程中表现出持续升高的梳理指数，但在放置在竞技场后立即出现短暂的运动激活。根据已发表的数据确定 FMRP 目标转录本和导致人类遗传神经发育障碍的突变的功能分析，我们提出以下蛋白质作为 FXS 中过度重复行为的候选介质：CaMKIIα、NMDA 受体亚基 2A 和 2B、NLGN3 和 SHANK3。总之，这些苍蝇突变表型和机制见解为药物发现提供了起点，以识别减少功能失调的重复行为的化合物。