Cell Biology: 一种导致轴突神经破裂的基因突变
为什么膝关节或者肘关节弯曲时，四肢的神经系统伸展，但不会被拉破？犹他州立大学的研究人员解释了其中的奥妙，他们发现一种弹力蛋白可以维持神经细胞的韧性。
研究人员发现，线虫体内该蛋白基因如果受到破坏，神经细胞也会破坏。这项发现为第5型脊髓小脑共济失调（spinocerebellar ataxia type 5，SCA5）提供了研究的参考基础。
SCA5是一种可能发生于各年龄层的神经退化性疾病，患者大脑中控制运动的神经细胞受到破坏，患者发生行走、谈话、写作和吞咽的障碍，甚至需要借助轮椅度过余生。研究结果刊载于1月29日的Cell Biology中。
这项研究核心是一种名为unc-70的线虫基因，unc-70转译的蛋白名为β血影蛋 白（beta spectrin）。人类共有四个β血影蛋白基因，每一个发生突变都会引起SCA5。
过去，研究人员认为，SCA5的病因是突变的β血影蛋白无法与神经细胞中特殊位置的其它蛋白结合，而导致细胞无法正常地传递讯息。但是在线虫进行的新研究证实，真正的原因是由于突变的β血影蛋白引起的神经细胞损伤。
研究人员发现线虫β血影蛋白突变后，线虫的神经元容易破裂；β血影蛋白如同微型弹簧，包被在神经细胞中，赋予神经细胞伸展性。他们认为突变基因可能与其它神经退化性疾病，如中风、运动损伤引发的大脑损伤有关。所以保护神经细胞中的血影蛋白，似乎能够减缓一些神经退化性疾病的恶化速度。
(资料来源 : Bio.com)
Nervous breakdown
An axon (arrow) snaps (top to bottom) in a worm lacking ß-spectrin
Like the waistband of your pants after Thanksgiving dinner, neurons have to be able to stretch and then return to shape. On page 269 Hammarlund et al. pinpoint the protein that confers this springiness, showing that neurons lacking the molecule fracture.Movements such as bending your elbow put strain on neurons, but the source of the cells' elasticity has been a mystery. Hammarlund et al. suspected that the protein ß-spectrin was involved. In red blood cells, the protein weaves into a mesh that supports the cell membrane, enabling erythrocytes to rebound after being crushed and dented during their travels through the circulatory system.
The researchers tested spectrin's function in neurons by observing nematodes that lack the protein. In embryonic worms, neurons grew normally between the animals' two nerve cords, indicating that spectrin isn't necessary for development. But after the worms hatched, their neurons began to display defects such as abnormal branching, frequent breaks, and signs of new growth, which doesn't normally occur after the embryonic stage. By tracking individual neurons, the scientists demonstrated that the breaks came first; the aberrant growth and misguided branches followed as worms attempted to repair the severed cells.
To determine whether movement snaps the neurons, the researchers scrutinized paralyzed animals. Few of their neurons broke. Hammarlund et al. conclude that the fragility of spectrin-lacking neurons might explain some kinds of neurodegenerative diseases. For example, patients with spinocerebellar ataxia type 5—an inherited form of paralysis that ran in Abraham Lincoln's family—carry a faulty ß-spectrin gene. Neurons might deteriorate in these patients because they break first, the researchers suggest.
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