Cellular and genetic basis underlying heterochronic brain development

大脑是动物最复杂的器官。由于它对生存起着至关重要的作用，脑功能和形态都面临着很高的选择压力。事实上，昆虫大脑的基本结构是高度保守的。然而，不同大脑部分(神经桩)的大小和形状反映了进化的适应。例如，蜜蜂嗅觉学习和记忆所需的蘑菇体被放大。然而，无论是在潜在的细胞发育过程水平上，还是在控制这些过程的基因水平上，对昆虫大脑形态的进化机制几乎一无所知。当比较昆虫之间的中枢复合体发育时，发现了一个有趣的适应：在半代谢昆虫中，中央身体(CB)的所有神经毛都在胚胎发生期间发育。这被认为是祖先的状况。果蝇是一个例外，因为CB只在幼虫后期和变态期间发育。赤粉虫Tribolium Castaneum是CB神经毛形成的中间产物，部分形成于胚胎发生过程中。在这个项目中，我们希望通过CB作为研究案例来了解异时发育进化中涉及的细胞和遗传机制。我们将以果蝇和Tribolium作为模型系统进行比较。我们一直在使用基因组编辑来建立工具来标记两个物种中的同源细胞/细胞组。在这个项目中，我们将比较从神经母细胞到成人神经回路的同源细胞的发育。这一分析将揭示在异时转变过程中，同源细胞在不同物种之间的发育路径何时以及如何分化。最后，我们想找出管理异时发育的基因调节器。

The brain is the most complex organ of an animal. Due to its essential role for survival, brain function and morphology are under high selective pressure. Indeed, the basic architecture of the brain is highly conserved within insects. However, size and shape of the different brain parts (neuropiles) reflect evolutionary adaptations. For instance, the mushroom bodies required for olfactory learning and memory are enlarged in bees. However, almost nothing is known about the mechanisms of evolution of insect brain morphology neither on the level of the underlying cellular developmental processes nor on the level of the genes that control these. An intriguing adaptation is found when comparing central complex development among insects: In hemimetabolous insects all neuropils of the central body (CB) develop during embryogenesis. This is supposed to be the ancestral condition. The fly Drosophila melanogaster represents an exception in that the CB develops only during late larval stages and metamorphosis. The red flour beetle Tribolium castaneum is an intermediate where the CB neuropils form partly during embryogenesis. In this project, we want to understand the cellular and genetic mechanisms involved in the evolution of heterochronic development by using the CB as study case. We will use Drosophila and Tribolium as model systems for comparison. We have been using genome editing in order to establish tools to mark homologous cells/cell groups in both species. In this project, we will compare the development of homologous cells from neuroblast to the adult circuitry. This analysis will reveal when and how the developmental paths of homologous cells diverge between species during the heterochronic shift. Finally, we want to identify genetic regulators that govern heterochronic development.