title: Systematic analysis of neural projections reveals clonal composition of the Drosophila brain.
abstract: BACKGROUND
  During development neurons are generated by sequential divisions of neural stem cells, or neuroblasts. In the insect brain progeny of certain stem cells form lineage-specific sets of projections that arborize in distinct brain regions, called clonal units. Though this raises the possibility that the entire neural network in the brain might be organized in a clone-dependent fashion, only a small portion of clones has been identified.
  
  
  RESULTS
  Using Drosophila melanogaster, we randomly labeled one of about 100 stem cells at the beginning of the larval stage, analyzed the projection patterns of their progeny in the adult, and identified 96 clonal units in the central part of the fly brain, the cerebrum. Neurons of all the clones arborize in distinct regions of the brain, though many clones feature heterogeneous groups of neurons in terms of their projection patterns and neurotransmitters. Arborizations of clones overlap preferentially to form several groups of closely associated clones. Fascicles and commissures were all made by unique sets of clones. Whereas well-investigated brain regions such as the mushroom body and central complex consist of relatively small numbers of clones and are specifically connected with a limited number of neuropils, seemingly disorganized neuropils surrounding them are composed by a much larger number of clones and have extensive specific connections with many other neuropils.
  
  
  CONCLUSIONS
  Our study showed that the insect brain is formed by a composition of cell-lineage-dependent modules. Clonal analysis reveals organized architecture even in those neuropils without obvious structural landmarks.
authors.affiliation: Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Ito
authors.forename: Naoki
authors.initials: N
authors.lastname: Masuda
authors.forename: Kazunori
authors.initials: K
authors.lastname: Shinomiya
authors.forename: Keita
authors.initials: K
authors.lastname: Endo
authors.forename: Kei
authors.initials: K
authors.lastname: Ito
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D019070:Cell Lineage; D002999:Clone Cells / Q000166:cytology / Q000378:metabolism; D004331:Drosophila melanogaster / Q000166:cytology / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D005260:Female; D007814:Larva / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018613:Microscopy, Confocal; D058953:Neural Stem Cells / Q000166:cytology / Q000378:metabolism; D019581:Neuropil / Q000166:cytology / Q000378:metabolism