Coordination of neural patterning in the Drosophila visual system - PubMed (original) (raw)

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Coordination of neural patterning in the Drosophila visual system

Maximilien Courgeon et al. Curr Opin Neurobiol. 2019 Jun.

Abstract

Precise formation of neuronal circuits requires the coordinated development of the different components of the circuit. Here, we review examples of coordination at multiples scales of development in one of the best-studied systems for neural patterning and circuit assembly, the Drosophila visual system, from coordination of gene expression in photoreceptors to the coordinated patterning of the different neuropiles of the optic lobe.

Copyright © 2019 Elsevier Ltd. All rights reserved.

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Conflict of interest statement

Conflict of interest statement

Nothing declared.

Figures

Figure 1:

Figure 1:

Fate specification in the retina: (a) Organization of the retinal mosaic. Yellow (y) and pale (p) ommatidia are randomly distributed in the retina, whereas DRA photoreceptors are localized in the last row of ommatidia at the dorsal margin of the retina (b) The three ommatidium subtypes and their Rhodopsin (Rh) expression. (c) Gene regulatory network controlling ommatidia subtype specification.

Figure 2:

Figure 2:

Building the retinotopic map in the lamina: (a) Retinotopic organization of the visual system. Colors represent three different retinotopic points along the A-P axis. Examples of neurons from the different neuropiles that are retinotopically organized (L2 in the lamina, Mi1 in the medulla and T4 and T5 in the lobula complex). (b) Sequence of lamina differentiation during larval development: the entry of photoreceptor axons into the lamina lead to the division of Lamina Precursors Cells (LPCs) and their assembly into lamina columns. This is followed by the entry of wrapping glia cell processes that will direct the differentiation of LPCs into differentiated lamina monopolar cells. As the eye disc grows more photoreceptor axons (in red) and glial cells enter the lamina leading to more columns being assembled posteriorly following a front of differentiation. Note that L5 neurons at the bottom of the lamina follow a different sequence than the other lamina neurons and do not depend on signaling from wrapping glia. (c) Schematic of the signaling activities required for the formation and differentiation of lamina neurons. (d) Schematic of the adult lamina. Note that each lamina cartridge is composed of one copy of each of the 5 lamina monopolar cells and 6 outer photoreceptors (R1-6).

Figure 3:

Figure 3:

Medulla development: (a) Representation of the larval brain showing the OPC lying on the lateral surface of the brain, below the eye disc. (b) In the OPC neuroepithelium cells are converted into neuroblasts that express a temporal sequence of transcription factors that generates neuronal diversity. During each window, different subtypes of neurons are produced (represented in colors). A Notch binary fate decision further increases diversity of each progeny by producing two distinct fates (striped vs non-striped neurons). (c) Cross section of the developing larval optic lobe showing the sequential formation of the medulla. The first neuroblast produces the most posterior medulla column. Over time more neuroepithelial cells are converted into neuroblasts that will add columns to the medulla anteriorly. (d) Overlay of the temporal patterning of neuroblasts and the sequential production of medulla columns. (e and f) Larval (e) and adult (f) schematics of the medulla representing how the regionalization of the OPC increases neuronal diversity. The uni-columnar neuron Mi1 is produced all along the OPC independently of the spatial compartments, whereas the three multi-columnar neurons Pm1,2 and 3 are only produced by progenitors from specific domains.

Figure 4:

Figure 4:

Retinotopic formation in the lobula plate: (a) Schematic of the lobula plate and the 4 subtypes of T4 (in red) and T5 neurons (in green). Each subtype targets to a different layer of the lobula plate neuropile (color coded for their response to motion direction, arrow on the side (b) Two neuroblasts give rise to the 4 T4s and T5s of a single column. Both go through two rounds of Notch mediated asymmetric decision and give rise to the 2 T4s and T5s of either the horizontal system for the Dpp+ neuroblast or of the vertical system for the Brk+ neuroblast.

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