Drosophila Neural Development

Abstract

The human brain is by far the most complex organ system in terms of cell type variety and interaction between cells. Studies from comparatively simple animal models allow us to genetically dissect the development and function of the nervous system. Advanced molecular genetic tools make the fruit fly Drosophila melanogaster a unique and powerful model system to study how during development a complex nervous system develops, how neurons and glia cells are generated and correctly assembled. Many key processes such as proliferation of neural stem cells, neurogenesis, orchestration of spatial and temporal identity, axon guidance and establishment of connectivity have been investigated in fruit flies. Comparative analysis shows that developmental processes as well as genetic pathways acting to build a complex brain are shared between mammals and insects.

Key Concepts:

  • Along the anteriorposterior and dorsoventral axes transcription factors pattern the nervous system.

  • Neural stem cells divide asymmetrically to self‐renew and generate committed neural precursors.

  • Different types of neural stem cells exist to establish different domains of the central nervous system.

  • Even though the brains of insects and mammals appear quite distinct the overall mode of development are similar.

Keywords: fruit fly; neurogenesis; axon guidance; synaptogenesis; neuronal stem cells

Figure 1.

Neuroblast formation and divisions. (a) The two domains of the neuroectoderm are delineated (dark red; PNE, procephalic neurectoderm; VNE, ventral neurectoderm) on the surface of a Drosophila embryo (A, anterior; D, dorsal; P, posterior; V, ventral). (b) Within the neurectoderm an equivalence group will be marked by the expression of proneural genes (blue). (c) As development progresses, one of the cells enlarges to become a neuroblast (NB), and surrounding cells are suppressed from becoming neuroblasts because of ‘lateral inhibition’. The neuroblast moves inward, delaminating from the epithelium. (d) The neuroblast divides asymmetrically giving rise to a smaller cell, a ganglion mother cell (GMC) (red). Prospero is inherited by the GMC but not by the neuroblast. (e) GMC divides once to give rise to neurons (brown) or glia (blue). If Gcm is present the postmitotic cell will develop into a glia cell.

Figure 2.

Nervous system patterning and postembryonic neurogenesis. (a) Schematic representation of the segmental organisation of the embryonic brain. The brain consists of three neuromeres (Pc, protocerebrum, Dc, deuterocerebrum and Tc, tritocerebrum) of the supraoesophageal ganglion and tree neuromeres (Md, mandibular; Mx, maxillary and Lb, labial neuromere) in the suboesophageal ganglion. Anterior brain domains are patterned by Otd and Ems, whereas the posterior brain and ventral nerve cord is patterned by Hox genes. The three columnar genes Vnd, Ind and Msh pattern the central nervous system dorsoventrally. (b) Temporal identity of neuroblasts and their progeny of lineage NB7‐1. Transient expression of the transcription factors Hb, Kr, Pdm and Cas control the development of U1–U5 motoneurons. (c) Postembryonic neurogenesis of the adult optic lobe occurs in the OPC, outer proliferation center; IPC, inner proliferation centre. In the central brain three distinct types of neuroblasts are found: Type I neuroblasts, Type II neuroblasts and Mushroom body neuroblasts (MB‐NBs).

Figure 3.

Drosophila visual system. (a) Cross‐section through the adult brain showing the right half including the eye, and the lamina (LA), medulla (ME) and lobula (LO) regions. The central brain (B) is located medial to the visual system. (b) An ommatidium showing photoreceptors R1 through R7; R8 receptor lies below R7 (not shown). (c) A third larval instar eye imaginal disc, showing the ‘morphogenetic furrow’ that divides the developing photoreceptor field behind the furrow and the undifferentiated field of cells ahead of the furrow.

Figure 4.

Axon guidance in the Drosophila ventral ganglion. (a) In wild type axons expressing Fra (dark blue) are attracted toward the midline; axons expressing Robo (red) run parallel to the midline, and can cross it only when axonal Robo is locally decreased (orange). fra or Net mutant: axons are not attracted toward the midline. robo or slit mutant: too many axons cross the midline. (b) Axon guidance of R7 (green) and R8 (blue) photoreceptors to the corresponding M6 and M7 layers in the medulla. R8 targeting is not occurring properly in gogo, fmi and caps mutants, whereas in NCad, Babo and dSmad2 mutants R7 targeting is affected.

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How to Cite close
Sprecher, Simon(Feb 2012) Drosophila Neural Development. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000791.pub2]