Tymanskyj Stephen R, Yang Benjamin, Falnikar Aditi, Lepore Angelo C, Ma Le
Department of Neuroscience, Vickie and Jack Farber Institute for Neuroscience, Sydney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
Department of Neuroscience, Vickie and Jack Farber Institute for Neuroscience, Sydney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
J Neurosci. 2017 Feb 8;37(6):1648-1661. doi: 10.1523/JNEUROSCI.3260-16.2017. Epub 2017 Jan 9.
Collateral branches from axons are key components of functional neural circuits that allow neurons to connect with multiple synaptic targets. Like axon growth and guidance, formation of collateral branches depends on the regulation of microtubules, but how such regulation is coordinated to ensure proper circuit development is not known. Based on microarray analysis, we have identified a role for microtubule-associated protein 7 (MAP7) during collateral branch development of dorsal root ganglion (DRG) sensory neurons. We show that MAP7 is expressed at the onset of collateral branch formation. Perturbation of its expression by overexpression or shRNA knockdown alters axon branching in cultured DRG neurons. Localization and time-lapse imaging analysis reveals that MAP7 is enriched at branch points and colocalizes with stable microtubules, but enters the new branch with a delay, suggesting a role in branch maturation. We have also investigated a spontaneous mutant mouse that expresses a truncated MAP7 and found a gain-of-function phenotype both and Further domain analysis suggests that the amino half of MAP7 is responsible for branch formation, suggesting a mechanism that is independent of its known interaction with kinesin. Moreover, this mouse exhibits increased pain sensitivity, a phenotype that is consistent with increased collateral branch formation. Therefore, our study not only uncovers the first neuronal function of MAP7, but also demonstrates the importance of proper microtubule regulation in neural circuit development. Furthermore, our data provide new insights into microtubule regulation during axonal morphogenesis and may shed light on MAP7 function in neurological disorders. Neurons communicate with multiple targets by forming axonal branches. In search of intrinsic factors that control collateral branch development, we identified a role for microtubule-associated protein 7 (MAP7) in dorsal root ganglion sensory neurons. We show that MAP7 expression is developmentally regulated and perturbation of this expression alters branch formation. Cell biological analysis indicates that MAP7 promotes branch maturation. Analysis of a spontaneous mouse mutant suggests a molecular mechanism for branch regulation and the potential influence of collateral branches on pain sensitivity. Our studies thus establish the first neuronal function of MAP7 and demonstrate its role in branch morphogenesis and neural circuit function. These findings may help in our understanding of the contribution of MAP7 to neurological disorders and nerve regeneration.
轴突的侧支是功能性神经回路的关键组成部分，它使神经元能够与多个突触靶点相连。与轴突生长和导向一样，侧支的形成依赖于微管的调节，但目前尚不清楚这种调节是如何协调以确保神经回路正常发育的。基于微阵列分析，我们确定了微管相关蛋白7（MAP7）在背根神经节（DRG）感觉神经元侧支发育过程中的作用。我们发现，MAP7在侧支形成开始时表达。通过过表达或shRNA敲低来干扰其表达，会改变培养的DRG神经元中的轴突分支。定位和延时成像分析表明，MAP7在分支点富集，并与稳定的微管共定位，但会延迟进入新分支，提示其在分支成熟中发挥作用。我们还研究了一种表达截短型MAP7的自发突变小鼠，发现其在[具体方面1]和[具体方面2]均表现出功能获得性表型。进一步的结构域分析表明，MAP7的氨基端负责分支形成，提示存在一种独立于其已知的与驱动蛋白相互作用的机制。此外，该小鼠表现出疼痛敏感性增加，这一表型与侧支形成增加一致。因此，我们的研究不仅揭示了MAP7的首个神经元功能，还证明了微管正常调节在神经回路发育中的重要性。此外，我们的数据为轴突形态发生过程中的微管调节提供了新见解，并可能揭示MAP7在神经疾病中的功能。神经元通过形成轴突分支与多个靶点进行通信。为了寻找控制侧支发育的内在因素，我们确定了微管相关蛋白7（MAP7）在背根神经节感觉神经元中的作用。我们发现，MAP7的表达受发育调控，干扰这种表达会改变分支形成。细胞生物学分析表明，MAP7促进分支成熟。对一种自发突变小鼠的分析提示了分支调节的分子机制以及侧支对疼痛敏感性的潜在影响。我们的研究因此确立了MAP7的首个神经元功能，并证明了其在分支形态发生和神经回路功能中的作用。这些发现可能有助于我们理解MAP7对神经疾病和神经再生的贡献。
