Distal arthrogryposis (DA) is a group of autosomal dominant skeletal muscle diseases characterized by congenital contractures of distal limb joints. The most common cause of DA is a mutation of the embryonic myosin heavy chain gene, MYH3. Human phenotypes of DA are divided into the weakest form–DA1, a moderately severe form–DA2B (Sheldon-Hall Syndrome), and a severe DA disorder–DA2A (Freeman-Sheldon Syndrome). As models of DA1 and DA2B do not exist, their disease mechanisms are poorly understood. We produced the first models of myosin-based DA1 (F437I) and DA2B (A234T) using transgenic Drosophila melanogaster and performed an integrative analysis of the effects of the mutations. Assessments included lifespan, locomotion, ultrastructural analysis, muscle mechanics, ATPase activity, in vitro motility, and protein modeling. We observed significant defects in DA1 and DA2B Drosophila flight and jump ability, as well as myofibril assembly and stability, with homozygotes displaying more severe phenotypes than heterozygotes. Notably, DA2B flies showed dramatically stronger phenotypic defects compared to DA1 flies, mirroring the human condition. Mechanical studies of indirect flight muscle fibers from DA1 heterozygotes revealed reduced power output along with increased stiffness and force production, compared to wild-type controls. Further, isolated DA1 myosin showed significantly reduced myosin ATPase activity and in vitro actin filament motility. These data in conjunction with our sinusoidal analysis of fibers suggest prolonged myosin binding to actin and a slowed step associated with Pi release and/or the power stroke. Our results are supported by molecular modeling studies, which indicate that the F437I and A234T mutations affect specific amino acid residue interactions within the myosin motor domain that may alter interaction with actin and nucleotide. The allele-specific ultrastructural and locomotory defects in our Drosophila DA1 and DA2B models are concordant with the differential severity of the human diseases. Further, the mechanical and biochemical defects engendered by the DA1 mutation reveal that power production, fiber stiffness, and nucleotide handling are aberrant in F437I muscle and myosin. The defects observed in our DA1 and DA2B Drosophila models provide insight into DA phenotypes in humans, suggesting that contractures arise from prolonged actomyosin interactions.

中文翻译：

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果蝇肌球蛋白突变体建模不同类型的严重性1型和2B型远侧关节型变态，并指示增强的肌动蛋白亲和力机制。

关节远端畸形（DA）是一组常染色体显性骨骼肌疾病，其特征是远端肢体先天性挛缩。DA的最常见原因是胚胎肌球蛋白重链基因MYH3突变。人的DA表型分为最弱的形式-DA1，中度严重的形式-DA2B（谢尔顿-霍尔综合征）和严重的DA障碍-DA2A（弗里曼-谢尔顿综合征）。由于不存在DA1和DA2B的模型，因此对其发病机理了解甚少。我们使用转基因果蝇（Drosophila melanogaster）生产了第一个基于肌球蛋白的DA1（F437I）和DA2B（A234T）模型，并对突变的影响进行了综合分析。评估包括寿命，运动，超微结构分析，肌肉力学，ATPase活性，体外运动性和蛋白质模型。我们观察到DA1和DA2B果蝇的飞行和跳跃能力以及肌原纤维的组装和稳定性均存在明显缺陷，纯合子比杂合子表现出更严重的表型。值得注意的是，与DA1苍蝇相比，DA2B苍蝇表现出明显更强的表型缺陷，这反映了人类的状况。对来自DA1杂合子的间接飞行肌纤维的机械研究表明，与野生型对照相比，功率输出减少，刚性和力产生增加。此外，分离的DA1肌球蛋白显示出明显降低的肌球蛋白ATPase活性和体外肌动蛋白丝运动性。这些数据与我们对纤维的正弦分析相结合，表明肌球蛋白与肌动蛋白的结合时间延长，与Pi释放和/或中风相关的步伐减慢。我们的结果得到分子模型研究的支持，这些研究表明F437I和A234T突变会影响肌球蛋白运动域内特定氨基酸残基的相互作用，从而可能改变与肌动蛋白和核苷酸之间的相互作用。果蝇DA1和DA2B模型中的等位基因特异性超微结构和运动缺陷与人类疾病的不同严重程度相一致。此外，由DA1突变引起的机械和生化缺陷表明F437I肌肉和肌球蛋白中的功率产生，纤维僵硬和核苷酸处理异常。在我们的DA1和DA2B果蝇模型中观察到的缺陷提供了对人类DA表型的洞察力，这表明挛缩症是由延长的放线菌素相互作用引起的。这表明F437I和A234T突变影响肌球蛋白运动域内特定的氨基酸残基相互作用，这可能会改变与肌动蛋白和核苷酸的相互作用。果蝇DA1和DA2B模型中的等位基因特异性超微结构和运动缺陷与人类疾病的不同严重程度相一致。此外，由DA1突变引起的机械和生化缺陷表明F437I肌肉和肌球蛋白中的功率产生，纤维僵硬和核苷酸处理异常。在我们的DA1和DA2B果蝇模型中观察到的缺陷提供了对人类DA表型的洞察力，这表明挛缩症是由延长的放线菌素相互作用引起的。这表明F437I和A234T突变影响肌球蛋白运动域内特定的氨基酸残基相互作用，这可能会改变与肌动蛋白和核苷酸的相互作用。果蝇DA1和DA2B模型中的等位基因特异性超微结构和运动缺陷与人类疾病的不同严重程度相一致。此外，由DA1突变引起的机械和生化缺陷表明F437I肌肉和肌球蛋白中的功率产生，纤维僵硬和核苷酸处理异常。在我们的DA1和DA2B果蝇模型中观察到的缺陷提供了对人类DA表型的洞察力，这表明挛缩症是由延长的放线菌素相互作用引起的。果蝇DA1和DA2B模型中的等位基因特异性超微结构和运动缺陷与人类疾病的不同严重程度相一致。此外，由DA1突变引起的机械和生化缺陷表明F437I肌肉和肌球蛋白中的功率产生，纤维僵硬和核苷酸处理异常。在我们的DA1和DA2B果蝇模型中观察到的缺陷提供了对人类DA表型的洞察力，这表明挛缩症是由延长的放线菌素相互作用引起的。果蝇DA1和DA2B模型中的等位基因特异性超微结构和运动缺陷与人类疾病的不同严重程度相一致。此外，由DA1突变引起的机械和生化缺陷表明F437I肌肉和肌球蛋白中的功率产生，纤维僵硬和核苷酸处理异常。在我们的DA1和DA2B果蝇模型中观察到的缺陷提供了对人类DA表型的洞察力，这表明挛缩症是由延长的放线菌素相互作用引起的。