Rett-causing mutations reveal two domains critical for MeCP2 function and for toxicity in MECP2 duplication syndrome mice.
Rett-causing mutations reveal two domains critical for MeCP2 function and for toxicity in MECP2 duplication syndrome mice.
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DOI：
10.7554/elife.02676
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发表时间：
2014-06-26
期刊：
影响因子：
7.7
通讯作者：
Zoghbi HY
中科院分区：
文献类型：
--
作者：
Heckman LD;Chahrour MH;Zoghbi HY
编码甲基-CpG结合蛋白2（MeCP 2）的X连锁基因的功能丧失导致进行性神经障碍Rett综合征（RTT）。相反，Xq 28的重复或三倍导致同样广泛的进行性神经系统疾病，MECP 2重复综合征，其特征与RTT有些重叠。为了了解MeCP 2功能在复制综合征中引起毒性，我们产生了表达内源性Mecp 2的小鼠模型，该Mecp 2沿着甲基-CpG结合结构域（MBD）或转录抑制结构域（TRD）中的RTT引起突变。我们确定，MBD和TRD都必须发挥作用，使MeCP 2加倍才有毒性。突变的MBD再现无效表型和表达的TRD突变体产生温和的RTT表型，但这两种突变是无害的，当与内源性Mecp 2表达。令人惊讶的是，突变TRD比删除整个C末端更有害，表明对MeCP 2功能的显性负效应，可能是由于基本簇的破坏。http://dx.doi.org/10.7554/eLife.02676.001雷特综合征是一种影响出生后大脑发育的疾病。患有这种疾病的婴儿正常发育，直到6-18个月大，当他们的语言和运动技能的发展停止，甚至倒退。大多数Rett综合征病例是由一种名为MECP 2的基因突变引起的。如果一个人错误地继承了MECP 2基因的额外拷贝，它可能会导致另一种发育障碍，称为MECP 2复制综合征。这种情况也会影响大脑，随着时间的推移会变得更糟，并与Rett综合征有许多共同特征。MECP 2基因的额外拷贝导致产生过多的MeCP 2蛋白。然而，这种蛋白质的水平加倍如何导致综合征，特别是蛋白质的哪些部分参与尚不清楚。此前，研究人员设计了表达人类MECP 2基因拷贝的小鼠，以及他们自己的基因版本。这些小鼠出现了类似于MECP 2复制综合征的病症，其中许多小鼠患有癫痫发作并在第一年内死亡。Heckman等人现在已经改造了小鼠，这些小鼠也具有额外的人类MECP 2基因，但具有导致人类Rett综合征的两种突变之一。一些小鼠的MeCP 2蛋白质的一部分发生了突变，该蛋白质与标记有称为甲基的小化学标签的DNA结合。其他小鼠在蛋白质的一个结构域中发生了突变，该结构域可以关闭基因。Heckman等人发现，具有这两种突变中的任何一种的额外MeCP 2蛋白的小鼠与正常小鼠一样健康，并且没有显示出MECP 2复制综合征的任何迹象。这表明这两个结构域必须是完整的，使MeCP 2蛋白的水平加倍才是有害的。此外，Heckman等人发现，MeCP 2中用于关闭基因的部分突变也会降低蛋白质与DNA结合的能力。下一个挑战是了解这种蛋白质水平加倍对大脑造成伤害的机制。还需要进一步的工作来揭示为什么有太多的MeCP 2蛋白或根本没有引起共享许多特征的综合征。DOI：http://dx.doi.org/10.7554/eLife.02676.002网站
Loss of function of the X-linked gene encoding methyl-CpG binding protein 2 (MeCP2) causes the progressive neurological disorder Rett syndrome (RTT). Conversely, duplication or triplication of Xq28 causes an equally wide-ranging progressive neurological disorder, MECP2 duplication syndrome, whose features overlap somewhat with RTT. To understand which MeCP2 functions cause toxicity in the duplication syndrome, we generated mouse models expressing endogenous Mecp2 along with a RTT-causing mutation in either the methyl-CpG binding domain (MBD) or the transcriptional repression domain (TRD). We determined that both the MBD and TRD must function for doubling MeCP2 to be toxic. Mutating the MBD reproduces the null phenotype and expressing the TRD mutant produces milder RTT phenotypes, yet both mutations are harmless when expressed with endogenous Mecp2. Surprisingly, mutating the TRD is more detrimental than deleting the entire C-terminus, indicating a dominant-negative effect on MeCP2 function, likely due to the disruption of a basic cluster. DOI: http://dx.doi.org/10.7554/eLife.02676.001 Rett syndrome is a disorder that affects the development of the brain after birth. Infants with this condition develop as normal until they are 6–18 months old, when the development of their language and motor skills stops, or even regresses. Most cases of Rett syndrome are caused by mutations in a gene called MECP2. If an individual mistakenly inherits an extra copy of the MECP2 gene, it can cause another developmental disorder called MECP2 duplication syndrome. This condition, which also affects the brain, gets worse over time and shares many features with Rett syndrome. The extra copy of the MECP2 gene leads to the production of too much MeCP2 protein. However, how doubling the level of this protein causes the syndrome and, in particular, which parts of the protein are involved are unknown. Previously, researchers engineered mice that expressed a copy of the human MECP2 gene alongside their own version of the gene. These mice developed a condition similar to MECP2 duplication syndrome and many of these mice suffered from seizures and died within their first year. Heckman et al. have now engineered mice that also have an extra human MECP2 gene but with one of two mutations that cause Rett syndrome in humans. Some mice had a mutation in a part of the MeCP2 protein that binds to DNA that is marked with small chemical tags called methyl groups. Other mice had a mutation in a domain of the protein that works to switch off genes. Heckman et al. found that mice with extra MeCP2 protein with either of these two mutations were as healthy as normal mice and showed none of the signs of MECP2 duplication syndrome. This indicates that both of these domains must be intact for doubling the levels of the MeCP2 protein to be harmful. Furthermore, Heckman et al. discovered that the mutation in the part of MeCP2 that works to switch genes off also reduces the protein's ability to bind to DNA. The next challenge is to understand the mechanism by which doubling the levels of this protein causes harm to the brain. Further work is also needed to uncover why having too much MeCP2 protein or none at all cause syndromes that share many features. DOI: http://dx.doi.org/10.7554/eLife.02676.002