Genomics Program and Division of Genetics, The Manton Center for Orphan Disease Research, Children's Hospital Boston, Boston, MA 02115, USA.
Hum Mol Genet. 2011 May 1;20(9):1712-25. doi: 10.1093/hmg/ddr047. Epub 2011 Feb 4.
In a forward genetic approach to identify novel genes for congenital muscle diseases, a zebrafish mutant, designated patchytail, was identified that exhibits degenerating muscle fibers with impaired motility behavior. Genetic mapping identified a genomic locus containing the zebrafish ortholog of the dystroglycan gene (DAG1). Patchytail fish contain a point mutation (c.1700T>A) in dag1, resulting in a missense change p.V567D. This change is associated with reduced transcripts and a complete absence of protein. The absence of α-dystroglycan and β-dystroglycan caused destabilization of dystroglycan complex, resulting in membrane damages. Membrane damage was localized on the extracellular matrix at myosepta as well as basement membrane between adjacent myofibers. These studies also identified structural abnormalities in triads at 3 days post fertilization (dpf) of dystroglycan-deficient muscles, significantly preceding sarcolemmal damage that becomes evident at 7 dpf. Immunofluorescence studies identified a subpopulation of dystroglycan that is expressed at t-tubules in normal skeletal muscles. In dag1-mutated fish, smaller and irregular-shaped t-tubule vesicles, as well as highly disorganized terminal cisternae of sarcoplasmic reticulum, were common. In addition to skeletal muscle defects, dag1-mutated fish have brain abnormalities and ocular defects in posterior as well as anterior chambers. These phenotypes of dystroglycan-deficient fish are highly reminiscent of the phenotypes observed in the human conditions muscle-eye-brain disease and Walker-Warburg syndrome. This animal model will provide unique opportunities in the understanding of biological functions of dystroglycan in a wide range of dystroglycanopathies, as disruption of this gene in higher vertebrates results in early embryonic lethality.
在一项鉴定先天性肌肉疾病新基因的正向遗传学方法中，鉴定出一种斑马鱼突变体，命名为斑鳍，其表现为运动行为受损的退行性肌纤维。遗传图谱定位到一个包含肌营养不良蛋白聚糖基因（DAG1）的斑马鱼直系同源物的基因组位点。斑鳍鱼在 dag1 中含有一个点突变（c.1700T>A），导致错义变化 p.V567D。这种变化与转录本减少和蛋白完全缺失有关。α-肌营养不良蛋白聚糖和β-肌营养不良蛋白聚糖的缺失导致肌营养不良蛋白聚糖复合物的不稳定，从而导致膜损伤。膜损伤定位于肌节的细胞外基质以及相邻肌纤维之间的基底膜。这些研究还在缺乏肌营养不良蛋白聚糖的肌肉中发现了三联体在受精后 3 天（dpf）的结构异常，显著早于在 7 dpf 时才变得明显的肌膜损伤。免疫荧光研究鉴定出正常骨骼肌中在 T 管表达的肌营养不良蛋白聚糖的亚群。在 dag1 突变鱼中，T 管囊泡较小且形状不规则，以及肌浆网终池高度紊乱，这些情况很常见。除了骨骼肌缺陷，dag1 突变鱼还具有脑异常和后前房的眼部缺陷。缺乏肌营养不良蛋白聚糖的鱼的这些表型与肌肉眼脑疾病和 Walker-Warburg 综合征等人类疾病中观察到的表型高度相似。这种动物模型将为理解肌营养不良蛋白聚糖在广泛的肌营养不良蛋白聚糖病中的生物学功能提供独特的机会，因为在高等脊椎动物中破坏该基因会导致早期胚胎致死。
