The development and function of neuronal subtypes processing color and skylight polarization in the optic lobes of Drosophila melanogaster. (March 2021)

• Record Type: Journal Article
• Authors: Sancer, Gizem; Wernet, Mathias F.
• Is Part Of: Arthropod structure & development. Volume 61(2021)
• Publication Date: 2021-03
• Subjects: Neural circuits -- Color vision -- Skylight polarization vision -- Neuronal cell types -- Circuit assembly and function -- Drosophila melanogaster; Arthropoda -- Morphology -- Periodicals; Arthropoda -- Anatomy -- Periodicals; Arthropoda -- Cytology -- Periodicals; Arthropods -- growth & development -- Periodicals; 595
• DOI: 10.1016/j.asd.2020.101012
• Languages: English
• ISSNs: 1467-8039

Abstract

Abstract: The retinal mosaics of many insects contain different ommatidial subtypes harboring photoreceptors that are both molecularly and morphologically specialized for comparing between different wavelengths versus detecting the orientation of skylight polarization. The neural circuits underlying these different inputs and the characterization of their specific cellular elements are the subject of intense research. Here we review recent progress on the description of both assembly and function of color and skylight polarization circuitry, by focusing on two cell types located in the distal portion of the medulla neuropil of the fruit fly Drosophila melanogaster 's optic lobes, called Dm8 and Dm9. In the main part of the retina, Dm8 cells fall into two molecularly distinct subtypes whose center becomes specifically connected to either one of randomly distributed 'pale' or 'yellow' R7 photoreceptor fates during development. Only in the 'dorsal rim area' (DRA), both polarization-sensitive R7 and R8 photoreceptors are connected to different Dm8-like cell types, called Dm-DRA1 and Dm-DRA2, respectively. An additional layer of interommatidial integration is introduced by Dm9 cells, which receive input from multiple neighboring R7 and R8 cells, as well as providing feedback synapses back into these photoreceptors. As a result, the response properties of color-sensitive photoreceptor terminals are sculpted towards being both maximally decorrelated, as well as harboring several levels of opponency (both columnar as well as intercolumnar). In the DRA, individual Dm9 cells appear to mix both polarization and color signals, thereby potentially serving as the first level of integration of different celestial stimuli. The molecular mechanisms underlying the establishment of these synaptic connections are beginning to be revealed, by using a combination of live imaging, developmental genetic studies, and cell type-specific transcriptomics. Highlights: Color and skylight polarization are processed via similar yet different cell types in the fly optic lobe. Two subtypes of Amacrine-like Dm8 cells with different spectral inputs in their center, integrate over a similar surrounding. A duplicated set of modality-specific Dm8-like cell types in the 'dorsal rim area' processes skylight polarization. Transcriptomic and developmental studies reveal the molecular mechanisms behind assembling these visual circuits. Dm9 cells provide a second layer of reciprocal, inter-ommatidial integration.