THE GENERATION OF NEURONAL DIVERSITY AND ITS EVOLUTION

Claude Desplan1,2, Nikos Konstantinides1, Felix Simon1, Neset Ozel1, Isabel Holguera1, Jennifer Malin1, Yen Chen1, and Bogdan Sieriebriennikov1

1 Center for Developmental Genetics, Department of Biology, New York University, New York, USA; 2 Center for Genomics and System Biology, NYU Abu Dhabi, UAE.

            In the Drosophila optic lobes, ~250 neuronal types organized as 800 columns process the inputs from 800 unit-eyes. Neural stem cells in the medulla sequentially express a series of temporal transcription factors (tTFs), producing at each temporal window different neurons that innervate each of the 800 columns.  We used single-cell mRNA sequencing to identify the tTFs that specify most medulla neurons. Each tTF regulates the progression of the series by activating the next tTF and repressing the previous one. Furthermore, the neuroepithelium that generates these stem cells is patterned into subdomains by spatial TFs: Although the series of tTFs is the same in stem cells originating from all spatial domains, the neurons they produce differ. Therefore, the integration of temporal and spatial patterning as well as Notch status, are sufficient to explain the generation of the entire neuronal diversity in this brain region.

            Finally, we will show how diversity in the brain can evolve to affect specific sensory functions in different species. I will describe the dramatically increased diversity in the mushroom body in ants as compared to flies, as ants rely extensively on pheromones rather than vision for their eusocial life.