Cellular and genetic basis underlying heterochronic brain development

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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.