Long Hong, Yoshikawa Shingo, Thomas John B
Molecular Neurobiology Laboratory, Salk Institute for Biological Studies, La Jolla, California 92037.
Molecular Neurobiology Laboratory, Salk Institute for Biological Studies, La Jolla, California 92037
J Neurosci. 2016 Jan 27;36(4):1140-50. doi: 10.1523/JNEUROSCI.3406-15.2016.
Receptors on the growth cone at the leading edge of elongating axons play critical guidance roles by recognizing cues via their extracellular domains and transducing signals via their intracellular domains, resulting in changes in direction of growth. An important concept to have emerged in the axon guidance field is the importance of repulsion as a major guidance mechanism. Given the number and variety of different repulsive receptors, it is generally thought that there are likely to be qualitative differences in the signals they transduce. However, the nature of these possible differences is unknown. By creating chimeras using the extracellular and intracellular domains of three different Drosophila repulsive receptors, Unc5, Roundabout (Robo), and Derailed (Drl) and expressing them in defined cells within the embryonic nervous system, we examined the responses elicited by their intracellular domains systematically. Surprisingly, we found no qualitative differences in growth cone response or axon growth, suggesting that, despite their highly diverged sequences, each intracellular domain elicits repulsion via a common pathway. In terms of the signaling pathway(s) used by the repulsive receptors, mutations in the guanine nucleotide exchange factor Trio strongly enhance the repulsive activity of all three intracellular domains, suggesting that repulsion by Unc5, Robo, and Drl, and perhaps repulsion in general, involves Trio activity.
A prevailing concept that has emerged in the axon guidance field is the importance of repulsion as a guidance mechanism for steering axons to their appropriate targets. Given the number and variety of different repulsive receptors, it is generally thought that there are differences in the signals that they transduce. However, this has never been tested directly. We have used the advanced genetics of Drosophila to compare directly the outputs of different repulsive receptors. Surprisingly, we found no qualitative differences in receptor-mediated repulsion, suggesting that, despite their highly diverged domain structure, each receptor couples to a common repulsive pathway. We went on to show that this common pathway involves Trio, a guanine nucleotide exchange factor known to promote cytoskeletal remodeling.
在伸长轴突前端生长锥上的受体，通过其胞外结构域识别线索并通过其胞内结构域转导信号，从而在生长方向改变中发挥关键的导向作用。轴突导向领域出现的一个重要概念是排斥作为主要导向机制的重要性。鉴于不同排斥受体的数量和种类，人们普遍认为它们转导的信号可能存在质的差异。然而，这些可能差异的本质尚不清楚。通过利用三种不同的果蝇排斥受体Unc5、Roundabout（Robo）和Derailed（Drl）的胞外和胞内结构域创建嵌合体，并在胚胎神经系统的特定细胞中表达，我们系统地研究了它们胞内结构域引发的反应。令人惊讶的是，我们发现生长锥反应或轴突生长没有质的差异，这表明尽管它们的序列高度不同，但每个胞内结构域都通过共同途径引发排斥。就排斥受体使用的信号通路而言，鸟嘌呤核苷酸交换因子Trio中的突变强烈增强了所有三个胞内结构域的排斥活性，这表明Unc5、Robo和Drl介导的排斥，也许一般的排斥，都涉及Trio活性。
轴突导向领域出现的一个普遍概念是排斥作为将轴突导向其合适靶点的导向机制的重要性。鉴于不同排斥受体的数量和种类，人们普遍认为它们转导的信号存在差异。然而，这从未被直接测试过。我们利用果蝇先进的遗传学直接比较了不同排斥受体的输出。令人惊讶的是，我们发现受体介导的排斥没有质的差异，这表明尽管它们的结构域结构高度不同，但每个受体都与共同排斥途径偶联。我们接着表明，这个共同途径涉及Trio，一种已知可促进细胞骨架重塑的鸟嘌呤核苷酸交换因子。
