Generation of Multiple Classes of V0 Neurons in Zebrafish Spinal Cord : Progenitor Heterogeneity and Temporal Control of Neuronal Diversity

发育中的脊髓被细分为不同的祖细胞域，每个祖细胞域产生不同类型的神经元。然而，负责在一个区域内产生神经元多样性的发育机制尚未得到很好的理解。在这里，我们研究了斑马鱼的V0神经元，那些来自p0祖域的神经元，来解决这个问题。我们发现所有的V0神经元都有互交轴突，但它们可以分为兴奋性和抑制性两类。V0兴奋性神经元（V0-e）根据其轴突运动轨迹可进一步分为三组；V0-eA（上升），V0-eB（分叉）和V0-eD（下降）神经元。通过对p0祖细胞及其后代的延时成像，我们发现抑制性和兴奋性神经元是由不同的祖细胞产生的。我们还证明了V0-eA神经元由不同的祖细胞产生，而V0-eB和V0-eD神经元由共同的祖细胞产生。然后，我们使用出生日期分析来揭示V0-eA、V0-eB和V0-eD神经元是按这个顺序出现的。通过干扰Notch信号和加速神经元分化，我们可以预见，早期出生的V0-e神经元的产生将以牺牲后期出生的神经元为代价。这些结果表明，多种类型的V0神经元由两种不同的机制产生；来自异种的p0祖细胞和来自相同的p0祖细胞，但以时间依赖的方式。

The developing spinal cord is subdivided into distinct progenitor domains, each of which gives rise to different types of neurons. However, the developmental mechanisms responsible for generating neuronal diversity within a domain are not well understood. Here, we have studied zebrafish V0 neurons, those that derive from the p0 progenitor domain, to address this question. We find that all V0 neurons have commissural axons, but they can be divided into excitatory and inhibitory classes. V0 excitatory neurons (V0-e) can be further categorized into three groups based on their axonal trajectories; V0-eA (ascending), V0-eB (bifurcating), and V0-eD (descending) neurons. By using time-lapse imaging of p0 progenitors and their progeny, we show that inhibitory and excitatory neurons are produced from different progenitors. We also demonstrate that V0-eA neurons are produced from distinct progenitors, while V0-eB and V0-eD neurons are produced from common progenitors. We then use birth-date analysis to reveal that V0-eA, V0-eB, and V0-eD neurons arise in this order. By perturbing Notch signaling and accelerating neuronal differentiation, we predictably alter the generation of early born V0-e neurons at the expense of later born ones. These results suggest that multiple types of V0 neurons are produced by two distinct mechanisms; from heterogeneous p0 progenitors and from the same p0 progenitor, but in a time-dependent manner.