Genetic Dissection of Trophic Interactions in the Larval Optic Neuropil of Drosophila Melanogaster

Dev Biol. 2005 Oct 15;286(2):549-58. doi: 10.1016/j.ydbio.2005.08.030. Epub 2005 Oct 5.


The larval visual system of Drosophila melanogaster consists of two bilateral clusters of 12 photoreceptors, which express Rhodopsin 5 and 6 (Rh5 and Rh6) in a non-overlapping manner. These neurons send their axons in a fascicle, the larval optic nerve (LON), which terminates in the larval optic neuropil. The LON is required for the development of a serotonergic arborization originating in the central brain and for the development of the dendritic tree of the circadian pacemakers, the small ventral lateral neurons (LNv) [Malpel, S., Klarsfeld, A., Rouyer, F., 2002. Larval optic nerve and adult extra-retinal photoreceptors sequentially associate with clock neurons during Drosophila brain development. Development 129, 1443-1453; Mukhopadhyay, M., Campos, A.R., 1995. The larval optic nerve is required for the development of an identified serotonergic arborization in Drosophila melanogaster. Dev. Biol., 169, 629-643]. Here, we show that both Rh5- and Rh6-expressing fibers overlap equally with the 5-HT arborization and that it, in turn, also contacts the dendritic tree of the LNv. The experiments described here aimed at determining whether Rh5- or Rh6-expressing fibers, as well as the LNv, influence the development of this serotonergic arborization. We conclude that Rh6-expressing fibers play a unique role in providing a signal required for the outgrowth and branching of the serotonergic arborization. Moreover, the innervation of the larval optic neuropil by the 5-HT arborization depends on intact Rac function. A possible role for these serotonergic processes in modulating the larval circadian rhythmicity and photoreceptor function is discussed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Circadian Rhythm
  • Dendrites
  • Drosophila Proteins / analysis*
  • Drosophila melanogaster / growth & development*
  • Eye / chemistry
  • Eye / embryology*
  • Larva
  • Nerve Fibers / chemistry
  • Neurons
  • Neuropil / chemistry*
  • Optic Nerve / embryology*
  • Rhodopsin / analysis*
  • Serotonin / physiology*
  • rac GTP-Binding Proteins / physiology


  • Drosophila Proteins
  • Rh6 protein, Drosophila
  • Serotonin
  • Rhodopsin
  • rac GTP-Binding Proteins