An inherited TUBB2B mutation alters a kinesin-binding site and causes polymicrogyria, CFEOM and axon dysinnervation
An inherited TUBB2B mutation alters a kinesin-binding site and causes polymicrogyria, CFEOM and axon dysinnervation
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DOI：
10.1093/hmg/dds393
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发表时间：
2012-12-15
影响因子：
3.5
通讯作者：
Engle, Elizabeth C.
中科院分区：
文献类型：
--
作者：
Cederquist, Gustav Y.;Luchniak, Anna;Engle, Elizabeth C.
微管是轴突引导机制的重要组成部分。在-微管蛋白突变中，只有TUBB3突变被证明会导致轴突引导的主要错误。所有已确定的TUBB2B突变都会导致多小回症，但尚不清楚TUBB2B突变是否会导致轴突神经失调作为主要表型。我们在TUBB2B中发现了一种新的遗传杂合错义突变，该突变导致一个家族中E421K氨基酸替代，该家族分离了先天性眼外肌纤维化（CFEOM）和多小回症。受影响家庭成员的大脑弥散张量成像显示，在互交投射神经元的轨迹畸变，这意味着缺乏同位连接。这些观察结果使我们询问轴突神经失调是否是主要表型，以及为什么E421K而不是其他TUBB2B替代导致CFEOM。外源性Tubb2b-E421K在发育中的胼胝体投射神经元中的表达足以扰乱同位连通性，而不影响神经元的产生或迁移。利用体外生化分析和酵母遗传学，我们发现TUBB2B-E421K -异源二聚体被纳入微管网络，在那里它们改变微管动力学并减少运动蛋白的定位。这些数据提供了TUBB2B突变可引起原发性轴突神经失调的证据。有趣的是，通过整合到微管中并改变其动态特性，E421K取代的行为不同于先前鉴定的TUBB2B取代，从而为产生的表型之间的差异提供了机制见解。与先前的研究一起，这些发现强调-微管蛋白同种型以保守和不同的方式支持人类神经系统的正常发育。
Microtubules are essential components of axon guidance machinery. Among -tubulin mutations, only those in TUBB3 have been shown to cause primary errors in axon guidance. All identified mutations in TUBB2B result in polymicrogyria, but it remains unclear whether TUBB2B mutations can cause axon dysinnervation as a primary phenotype. We have identified a novel inherited heterozygous missense mutation in TUBB2B that results in an E421K amino acid substitution in a family who segregates congenital fibrosis of the extraocular muscles (CFEOM) with polymicrogyria. Diffusion tensor imaging of brains of affected family members reveals aberrations in the trajectories of commissural projection neurons, implying a paucity of homotopic connections. These observations led us to ask whether axon dysinnervation is a primary phenotype, and why the E421K, but not other, TUBB2B substitutions cause CFEOM. Expression of exogenous Tubb2b-E421K in developing callosal projection neurons is sufficient to perturb homotopic connectivity, without affecting neuronal production or migration. Using in vitro biochemical assays and yeast genetics, we find that TUBB2B-E421K -heterodimers are incorporated into the microtubule network where they alter microtubule dynamics and can reduce kinesin localization. These data provide evidence that TUBB2B mutations can cause primary axon dysinnervation. Interestingly, by incorporating into microtubules and altering their dynamic properties, the E421K substitution behaves differently than previously identified TUBB2B substitutions, providing mechanistic insight into the divergence between resulting phenotypes. Together with previous studies, these findings highlight that -tubulin isotypes function in both conserved and divergent ways to support proper human nervous system development.