The functional diversity of cell types underlying colour vision in Drosophila

• Applicant: Dr. Christopher Schnaitmann
• Subject Area: Cognitive, Systems and Behavioural Neurobiology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449783245

Light reaching the retina contains lots of information about the environment, such as the colour of objects, their shape and the direction in which they are moving. All these features have to be computed from photoreceptor signals in subsequent neural circuits to ultimately guide behavioural responses. Here, we aim to reveal the microcircuitry of pathways in the visual system underlying colour vision. To understand the computations performed by these pathways and their role in colour guided behaviour, we are studying colour vision in Drosophila. A hallmark of colour vision is the comparison of signals of photoreceptor classes with different spectral sensitivity by colour-opponent neurons. We recently disclosed that such processing, similar as in the mammalian retina, is already implemented in the terminals of specific photoreceptor types in Drosophila. Whether the two distinct photoreceptor-opponencies with UVshort/blue-sensitivity and UVlong/green-sensitivity are conveyed by parallel downstream pathways and what kind of computations postsynaptic neurons implement remains unknown. Several neural cell types downstream of these photoreceptors have been identified. Given that many of them receive input from different ommatidia, they likely contribute to spatial processing of spectral information. Two-photon calcium imaging in neurons expressing genetically encoded calcium indicators in combination with a multi-spectral spatial stimulation adapted to the fly visual system will allow the identfication of colour-processing cell types and reveal their spectral, spatial, and temporal response properties. Guided by connectomic and single cell RNAseq data of the fly visual system, we will genetically manipulate neural activity and expression of neurotransmission related genes in specific circuit elements. This approach will reveal how complex physiological properties of neurons like spatial receptive fields are shaped by the interaction of individual cell types and identify the underlying molecular mechanisms. We will also conduct colour choice experiments combined with genetic pertubation of neural function to disclose the role of specific cell types in colour guided behaviour. Thereby, knowledge of the response properties of a cell type will enable a directed approach. In contrast to previous studies, these experiments will employ a wide range of spectral stimuli with variable spatial properties, that will also allow analysing the role of stimulus size and spatial colour contrast in colour discrimination. Together, by identifying relevant computations, underlying molecular and circuit mechanisms and their role in colour guided behaviour, the proposed work will contribute to a detailed mechanistic understanding of colour vision in an insect model.

• DFG Programme: Research Grants
• Major Instrumentation: Custom Built Two-photon Microscope w/o Laser
• Instrumentation Group: 5090 Spezialmikroskope