공지사항

2023-2 BK 특별세미나 안내 : Dr. Suguru Takagi

작성일 2023-12-19

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Abstract
Brains display incredible diversity in neuron number between animal species. Evolutionary increases in the number of neurons occur not only through the emergence of new cell types but also through expansion of pre-existing neuronal populations. Of the latter phenomenon, some of the most spectacular examples are in sensory systems. From the star-nosed mole’s eponymous mechanosensory organ to the platypus’ electroreceptive bill, the expansion of sensory neuron populations detecting important environmental cues is a widespread evolutionary phenomenon in animals. However, how such neuron increases contribute to improved sensory detection and behaviour remain largely unexplained.
Here we address this question through comparative analysis of olfactory pathways in Drosophila melanogaster and its close relative Drosophila sechellia, which feeds and breeds exclusively on Morinda citrifolia noni fruit. We show that D. sechellia displays selective, large expansions of noni-detecting olfactory sensory neuron (OSN) populations, and that this trait has a multigenic basis. In noni odour plume-tracking assays, D. sechellia exhibits enhanced performance compared to D. melanogaster. Through activation and inhibition of defined proportions of one noni-sensing OSN population, we establish that increased neuron numbers contribute to this behavioural persistence. These expansions are accompanied by an increase in synaptic connections between OSNs and their projection neuron (PN) partners that transmit information to higher brain centres. Quantification of odour-evoked responses of partner OSNs and PNs reveals that OSN population expansions do not lead to heightened PN sensitivity, beyond that due to sensory receptor tuning differences. Rather, these pathways – but not those with conserved OSN numbers – exhibit non-adapting PN activity upon odour stimulation. Our work reveals an unexpected functional impact of sensory neuron expansions that can synergise with peripheral receptor tuning changes to explain ecologically-relevant, species-specific behaviour.