Xie G, Clapcote S J, Nieman B J, Tallerico T, Huang Y, Vukobradovic I, Cordes S P, Osborne L R, Rossant J, Sled J G, Henderson J T, Roder J C
Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Canada.
Genes Brain Behav. 2007 Nov;6(8):717-27. doi: 10.1111/j.1601-183X.2007.00302.x. Epub 2007 Mar 21.
Dominant mutations of the P/Q-type Ca(2+) channel (CACNA1A) underlie several human neurological disorders, including episodic ataxia type 2, familial hemiplegic migraine 1 (FHM1) and spinocerebellar ataxia 6, but have not been found previously in the mouse. Here we report the first dominant ataxic mouse model of Cacna1a mutation. This Wobbly mutant allele of Cacna1a was identified in an ethylnitrosourea (ENU) mutagenesis dominant behavioral screen. Heterozygotes exhibit ataxia from 3 weeks of age and have a normal life span. Homozygotes have a righting reflex defect from postnatal day 8 and later develop severe ataxia and die prematurely. Both heterozygotes and homozygotes exhibit cerebellar atrophy with focal reduction of the molecular layer. No obvious loss of Purkinje cells or decrease in size of the granule cell layer was observed. Real-time polymerase chain reaction revealed altered expression levels of Cacna1g, Calb2 and Th in Wobbly cerebella, but Cacna1a messenger RNA and protein levels were unchanged. Positional cloning revealed that Wobbly mice have a missense mutation leading to an arginine to leucine (R1255L) substitution, resulting in neutralization of a positively charged amino acid in repeat III of voltage sensor segment S4. The dominance of the Wobbly mutation more closely resembles patterns of CACNA1A mutation in humans than previously described mouse recessive mutants (tottering, leaner, rolling Nagoya and rocker). Positive-charge neutralization in S4 has also been shown to underlie several cases of human dominant FHM1 with ataxia. The Wobbly mutant thus highlights the importance of the voltage sensor and provides a starting point to unravel the neuropathological mechanisms of this disease.
P/Q型钙通道（CACNA1A）的显性突变是几种人类神经系统疾病的基础，包括发作性共济失调2型、家族性偏瘫性偏头痛1型（FHM1）和脊髓小脑共济失调6型，但此前在小鼠中尚未发现。在此，我们报告了首个Cacna1a突变的显性共济失调小鼠模型。在乙基亚硝基脲（ENU）诱变显性行为筛选中鉴定出Cacna1a的这个“摇摆”突变等位基因。杂合子从3周龄开始出现共济失调，寿命正常。纯合子从出生后第8天开始出现翻正反射缺陷，随后发展为严重共济失调并过早死亡。杂合子和纯合子均表现出小脑萎缩，分子层局部变薄。未观察到明显的浦肯野细胞丢失或颗粒细胞层大小减小。实时聚合酶链反应显示，“摇摆”小鼠小脑中Cacna1g、Calb2和Th的表达水平发生改变，但Cacna1a信使核糖核酸和蛋白质水平未变。定位克隆显示，“摇摆”小鼠存在一个错义突变，导致精氨酸被亮氨酸取代（R1255L），从而使电压传感器片段S4的重复III中的一个带正电荷的氨基酸被中和。与先前描述的小鼠隐性突变体（蹒跚、瘦弱、滚动名古屋和摇摆）相比，“摇摆”突变的显性更类似于人类CACNA1A突变的模式。S4中的正电荷中和也被证明是几例伴有共济失调的人类显性FHM1病例的基础。因此，“摇摆”突变体突出了电压传感器的重要性，并为阐明该疾病的神经病理机制提供了一个起点。
