This, in turn, induces a defect in the dendrites of lobula plate tangential cells (LPTCs), which are postsynaptic to T4/T5 neurons. Layer-specific innervation of T4/T5 dendrites and axons is lost upon SoxN or Sox102F knockdown. Drawing summarizing the anatomical and behavioral phenotypes observed upon specific disruption of SoxN or Sox102F in T4/T5 neurons. When this process fails, some postsynaptic partners of T4/T5 neurons also exhibit aberrant morphologies, which affects the proper functioning of the fly motion sensing circuits (Figure 2) (Schilling et al., 2019).įigure 2. We have found that SoxN and Sox102F, two members of the SOX family of transcription factors, are required in all T4 and T5 neurons during their maturation in order to restrict their dendrites and axons into single synaptic layers. A common attribute of T4 and T5 neurons is the layer-specific innervation displayed by their dendrites and axons (Figure 1) (Fischbach and Dittrich, 1989), which is thought to support precise synaptic connectivity. This specialization results from their dendrites arborizing in different neuropil regions (T4 dendrites in the medulla, T5 dendrites in the lobula) and therefore receiving synaptic input from different neuronal types. While T4 neurons respond to motion of brightness increments, T5 neurons detect motion of brightness decrements (Maisak et al., 2013). The dendrites of T4 and T5 neurons represent the first processing stage in the fly visual system in which the direction of image motion is encoded. To address this question, we use the T4/T5 neurons of the Drosophila visual system as a model because of their genetic accessibility and the extensive knowledge we have about their morphology and physiology. How neurons acquire a diverse repertoire of structural and functional properties in order to establish working neural circuits remains poorly understood. The axon terminal of the labelled T4 neuron is restricted to lobula plate layer 3. The four layers of the lobula plate are visualized by staining Bruchpilot (in magenta). Right panel: Drosophila optic lobe with a single T4 neuron labelled with GFP (in green). T4 dendrites arborize only in medulla layer M10, while T5 dendrites arborize only in lobula layer Lo1. Connectin signal is very high in medulla layer M9 and lobula layer Lo3. Neuropil layers are visualized by staining DN-cadherin (in grey) and Connectin (in red). Left panel: Drosophila optic lobe with all T4/T5 neurons labelled with GFP (in green).
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