Project (Gregor Bucher)

Evolution of neural stem cell diversity in insect brains

Background: The brain is among the most complex organs of an animal, where sensory inputs and internal states are processed to guide its behavior. Hence, modifications of brain structure and function in response to specific environmental conditions is paramount for each species’ adaptation. Insects represent one of the most diverse animal clades and they have conquered almost every habitat on earth. Indeed, based on the highly conserved basic bauplan within the insect clade, brains have diversified significantly in size, shape and position of their functional brain units, the neuropils. For instance, the mushroom bodies required for olfactory learning and memory are enlarged in bees, antennal lobes are reduced in aquatic beetles and the size of the optic lobes is increased in species that navigate in complex environments. Divergent brain morphologies emerge during embryonic and postembryonic ontogeny and, hence, any evolutionary modification depends on a modification of developmental mechanisms. It is believed that the basic developmental processes are conserved. However, it remains enigmatic, when and at what level of embryonic development is modified in order to direct development to form diverse brains.
Evolution of neural stem cell identity: The insect brain is built from neural stem cells (neuroblasts, NBs), which divide asymmetrically to form neurons and glia. The number of NBs differs between species but it is unknown, what NBs were lost or added because respective markers are lacking. Each NB acquires a distinct identity by the positional information in the neuroectoderm. Specifically, different “cocktails” of transcription factors that are expressed in the NBs determine their positional identity. These cocktails are only partially described in Drosophila but completely enigmatic in other insects.

The project: In this project, we want to use the power of single cell sequencing in order to determine the entire transcription factor cocktails of all neuroblasts in the red flour beetle Tribolium castaneum. We will use genome editing in order to generate transgenic lines with fluorescently marked neuroblasts. Then, NBs will be isolated and sequenced. The resulting data will be compared to similar data from Drosophila (generated by our collaborators or by us). This work will for the first time determine the comprehensive transcription factor cocktail in an insect outside Drosophila and it will allow judging, which NBs are conserved and which are diverged between these species. Further, we will use single and double knock-down RNAi experiments in order to alter the identity of selected neuroblasts in order to test the emerging hypotheses on identity specification.

Techniques applied:
- Genome editing
- Isolation of single stem cells or their nuclei
- Single cell sequencing and bioinformatics analyses
- RNAi knock-down

Homepage Research Group

For more information see for instance:
  • Farnworth et al. (in review at PlosBiol) Sequence heterochrony led to a gain of functionality in an immature stage of the central complex: a fly-beetle insight
  • He B, Büscher M, Farnworth M.S, Strobl F, Stelzer E, Koniszewski NDB, Mühlen D, Bucher G (2019) An ancestral apical brain region contributes to the central complex under the control of foxQ2 in the beetle Tribolium eLife 2019;8:e49065
  • Koniszewski*, NDB, Kollmann* M, Bigham M, Farnworth M, He B, Büscher M, Hütteroth W, Binzer M, Schachtner J, Bucher, G. The insect central complex as model for heterochronic brain development-background, concepts, and tools. Dev. Genes Evol. 2016;226:209-19.