Cell surface control of the layer specific targeting in the Drosophila visual system.

Satoko Hakeda-Suzuki,Takashi Suzuki

doi:10.1266/ggs.89.9

Satoko Hakeda-Suzuki, Takashi Suzuki

Open Access

https://doi.org/10.1266/ggs.89.9

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Abstract

To achieve the precise wiring of axons in the brain required to form a fine architecture, a molecular level interaction between axons and their targets is necessary. The Drosophila visual system has a layered and columnar structure which is often found in the brain of vertebrates. With powerful genetic tools for its analysis, the Drosophila visual system provides a useful framework to examine the molecular mechanisms of axon targeting specificity. The medulla is the second optic ganglion in the Drosophila optic lobe, and is subdivided into ten layers. Among the eight photoreceptor types, R7 and R8 pass through the first optic ganglion lamina and innervate the medulla. In the medulla, R7 and R8 axons grow in a distinct manner to reach their final target layers: M6 and M3, respectively. The axons from R7 and R8 take characteristic steps to extend toward their target layer. In this review, we discuss the formation of the Drosophila optic lobe and the molecular mechanisms of layer specific targeting of R8 axons in the medulla. Fundamental and comprehensive understanding of the crosstalk of growing axons and target regions in the Drosophila optic lobe will elucidate the general principles applicable to more complex nervous systems.

Highlights

During the formation of neuronal circuits, axons find their appropriate targets and form synapses with them to selectively generate a functional network
The molecular mechanisms underlying the formation of the Drosophila visual system have been widely reported, but here we focus our discussion on the function of the molecules that control the targeting of the R8 axon to the distinct medulla layer M3
Phospho-mimicking Golden goal (Gogo) enhances the adhesiveness of the R8 axon to the R8 temporary layer, and Gogo is phosphorylated at an early stage of pupal development, the biological relevance of the phosphorylation has to be further examined, as dephosphorylated Gogo can apparently rescue the R8 axon targeting of gogo mutant flies

Summary

INTRODUCTION

During the formation of neuronal circuits, axons find their appropriate targets and form synapses with them to selectively generate a functional network. Neurons in the brains are wired vertically and horizontally with astounding precision and fidelity, which enables the network to efficiently process and propagate neuronal information (Huberman et al, 2010). To achieve this incredibly complex wiring, neurons should extend their axons between the numerous axons and dendrites of other neurons during development, mak-. We first survey the development of the layered and columnar structure of the Drosophila visual system, and discuss the molecular agents involved in the layer-specific targeting of photoreceptor axons. The hormonal control of neuronal development, as well as recent advances in genome editing in Drosophila, is reviewed in this issue (Niwa and Niwa, 2014; Kondo, 2014)

DEVELOPMENT OF THE DROSOPHILA VISUAL SYSTEM

Lamina cartridge

GOLDEN GOAL AND FLAMINGO

Fra Netrin

NETRIN AND FRAZZLED

CONCLUSION AND PERSPECTIVES