Department of Cell Biology, University of Virginia, Charlottesville, VA 22908.
Department of Anatomy and Cell Biology, Brody School of Medicine, East Carolina University, Greenville, NC 27834.
Mol Biol Cell. 2019 May 1;30(10):1214-1229. doi: 10.1091/mbc.E18-06-0361. Epub 2019 Mar 6.
Correct wiring in the neocortex requires that responses to an individual guidance cue vary among neurons in the same location, and within the same neuron over time. Nestin is an atypical intermediate filament expressed strongly in neural progenitors and is thus used widely as a progenitor marker. Here we show a subpopulation of embryonic cortical neurons that transiently express nestin in their axons. Nestin expression is thus not restricted to neural progenitors, but persists for 2-3 d at lower levels in newborn neurons. We found that nestin-expressing neurons have smaller growth cones, suggesting that nestin affects cytoskeletal dynamics. Nestin, unlike other intermediate filament subtypes, regulates cdk5 kinase by binding the cdk5 activator p35. Cdk5 activity is induced by the repulsive guidance cue Semaphorin3a (Sema3a), leading to axonal growth cone collapse in vitro. Therefore, we tested whether nestin-expressing neurons showed altered responses to Sema3a. We find that nestin-expressing newborn neurons are more sensitive to Sema3a in a roscovitine-sensitive manner, whereas nestin knockdown results in lowered sensitivity to Sema3a. We propose that nestin functions in immature neurons to modulate cdk5 downstream of the Sema3a response. Thus, the transient expression of nestin could allow temporal and/or spatial modulation of a neuron's response to Sema3a, particularly during early axon guidance.
新皮层中的正确布线要求同一位置的神经元对单个导向线索的反应各不相同，并且随着时间的推移，同一神经元内的反应也各不相同。巢蛋白是一种在神经祖细胞中强烈表达的非典型中间丝，因此被广泛用作祖细胞标记物。在这里，我们展示了一小部分胚胎皮质神经元，其轴突中瞬时表达巢蛋白。因此，巢蛋白的表达不仅限于神经祖细胞，而是在新生神经元中以较低水平持续表达 2-3 天。我们发现表达巢蛋白的神经元的生长锥较小，这表明巢蛋白影响细胞骨架动力学。巢蛋白与其他中间丝亚型不同，通过结合 cdk5 激活剂 p35 来调节 cdk5 激酶。cdk5 活性被排斥性导向线索 Semaphorin3a (Sema3a) 诱导，导致体外轴突生长锥塌陷。因此，我们测试了表达巢蛋白的神经元对 Sema3a 的反应是否发生改变。我们发现，表达巢蛋白的新生神经元对 Sema3a 的敏感性更高，以 roscovitine 敏感的方式，而巢蛋白敲低则导致对 Sema3a 的敏感性降低。我们提出，巢蛋白在未成熟神经元中发挥作用，以调节 Sema3a 反应下游的 cdk5。因此，巢蛋白的短暂表达可以允许神经元对 Sema3a 的反应进行时间和/或空间调节，特别是在早期轴突导向期间。
