Sharp D J, Kuriyama R, Essner R, Baas P W
Department of Anatomy, University of Wisconsin Medical School, Madison 53706, USA.
J Cell Sci. 1997 Oct;110 ( Pt 19):2373-80. doi: 10.1242/jcs.110.19.2373.
Neurons extend two types of processes with distinct morphologies and patterns of microtubule polarity orientation. Axons are thin cylindrical processes containing microtubules that are uniformly oriented with their plus-ends-distal to the cell body while dendrites are stout tapering processes that contain nonuniformly oriented microtubules. We have proposed that these distinct microtubule patterns are established by molecular motors that transport microtubules into each type of process with the appropriate orientation. To test the feasibility of this proposal, we have embarked on a series of studies involving the expression of vertebrate motors in insect Sf9 cells. We previously focused on a kinesin-related protein termed CHO1/MKLP1, which localizes to the midzone of the mitotic spindle, and which has been shown to have the appropriate properties to transport microtubules of opposite orientation relative to one another. Expression of a fragment of CHO1/MKLP1 containing its motor domain induces Sf9 cells to extend processes with a stout tapering morphology and a nonuniform microtubule polarity pattern similar to dendrites. Here we focus on a minus-end-directed kinesin-related motor protein termed CHO2, which localizes to the non-overlapping regions of the mitotic spindle, and which has been shown to have the appropriate properties to transport microtubules with plus-ends-leading. Sf9 cells induced to express a fragment of CHO2 containing its motor domain extend processes with a long cylindrical morphology and a uniformly plus-end-distal microtubule polarity pattern similar to axons. These results show that motor proteins have the capacity to organize distinct patterns of microtubule polarity orientation during process outgrowth, and that these patterns are intimately related to the unique morphological characteristics of the processes. Moreover, mutation of three amino acids corresponding to the ATP binding site necessary for motor function suppresses the capacity of the CHO2 fragment to induce process formation and microtubule reorganization, indicating that at least in the case of CHO2, the transport properties of the motor are essential for it to elicit these effects.
神经元延伸出两种具有不同形态和微管极性取向模式的突起。轴突是细的圆柱形突起，含有微管，这些微管的正端向远离细胞体的方向均匀取向，而树突是粗壮的逐渐变细的突起，含有取向不均匀的微管。我们提出，这些不同的微管模式是由分子马达建立的，这些分子马达将微管以适当的取向运输到每种类型的突起中。为了测试这一建议的可行性，我们开展了一系列研究，涉及在昆虫Sf9细胞中表达脊椎动物马达。我们之前专注于一种名为CHO1/MKLP1的驱动蛋白相关蛋白，它定位于有丝分裂纺锤体的中间区，并且已被证明具有将相反取向的微管相互运输的适当特性。包含其马达结构域的CHO1/MKLP1片段的表达诱导Sf9细胞延伸出具有粗壮逐渐变细形态和类似于树突的不均匀微管极性模式的突起。在这里，我们专注于一种名为CHO2的负端定向驱动蛋白相关马达蛋白，它定位于有丝分裂纺锤体的非重叠区域，并且已被证明具有将微管正端向前运输的适当特性。诱导表达包含其马达结构域的CHO2片段的Sf9细胞延伸出具有长圆柱形形态和类似于轴突的均匀正端向远微管极性模式的突起。这些结果表明，马达蛋白有能力在突起生长过程中组织不同的微管极性取向模式，并且这些模式与突起的独特形态特征密切相关。此外，对应于马达功能所需的ATP结合位点的三个氨基酸的突变抑制了CHO2片段诱导突起形成和微管重组的能力，表明至少在CHO2的情况下，马达的运输特性对于其引发这些效应至关重要。
