Evolutionary shifts in the developmental control of neuron number

不同物种的大脑大小差异很大，这在很大程度上是由发育过程中神经元产生的差异解释的。虽然我们对某些研究很好的物种中控制神经元产生的发育机制有一些了解，但我们才刚刚开始探索这些发育机制是如何改变以促进神经元数量的进化的。了解神经变异的最近基础对于进化神经科学中的各种问题至关重要，从识别大脑进化中的潜在限制和权衡，到探索神经特征和行为变异之间的关系。这个项目的目的是利用新热带蝴蝶的一个不同部落--海里尼尼作为一个研究系统来解决这些问题。我们最近发现，大脑中对学习和记忆特别重要的一个区域--蘑菇体--在赫利柯尼尼蝴蝶中的变化超过25倍。这种极端的变异是由形成蘑菇体的凯尼恩细胞(Kenyon Cell)数量的大规模扩张推动的。我们现在想要了解凯尼恩细胞数量的这种变化是如何由不同物种之间神经发生的发育控制的变化决定的。该项目的主要目标是测试四个过程的作用，所有这四个过程都可以改变细胞生产，在塑造赫利柯尼尼的Kenyon细胞数量方面：i)神经发生开始时神经母细胞数量增加，ii)神经发生期间细胞周期加快，iii)神经发生持续时间延长，iv)神经母细胞凋亡模式减少或延迟。这项工作将通过比较不同物种的发育模式来完成，这些物种在凯尼恩细胞中以已知的方式发生变化。这将为我们理解不同物种间凯尼恩细胞神经发生的差异奠定基础。随后的工作将利用这一基础来研究我们实验室确定的调控蘑菇体进化的候选基因的功能效应。

Brain size varies massively across species, often largely explained by variation in the production of neurons during development. Although we have some knowledge of the developmental mechanisms controlling neuron production in certain well studied species, we are only beginning to explore how these developmental mechanisms change to facilitate the evolution of neuron number. Understanding the proximate basis of neural variation is critical for diverse questions in evolutionary neuroscience, from identifying potential constraints and trade-offs in brain evolution, to explore relationships between neural traits and behavioural variation. This project aims to tackle these questions using Heliconiini, a diverse tribe of Neotropical butterflies, as a study system. We have recently shown that one region of the brain that has particular importance in learning and memory, the mushroom bodies, varies by over 25X across Heliconiini butterflies. This extreme variation is driven by a massive expansion in the number of Kenyon cells, neurons that form the mushroom body. We now want to understand how this variation in Kenyon cell number is determined by changes in the developmental control of neurogenesis across species. The primary goals of the project are to test the role of four processes, all of which could alter cell production, in shaping Kenyon cell number across Heliconiini: i) increased neuroblast number at the onset of neurogenesis, ii) accelerated cell-cycle rates during neurogenesis, iii) extension in the duration of neurogenesis, iv) reduced or delayed patterns of apoptosis of neuroblasts. This work will be performed by comparing patterns of development across species which vary in Kenyon cell in known ways. It will form the foundation of our understanding of how Kenyon cell neurogenesis varies across species. Subsequent work will use this foundation to study the functional effects of candidate genes identified by our lab as regulators of mushroom body evolution.