Tiling of r7 axons in the Drosophila visual system is mediated both by transduction of an activin signal to the nucleus and by mutual repulsion.
The organization of neuronal wiring into layers and columns is a common feature of both vertebrate and invertebrate brains. In the Drosophila visual system, each R7 photoreceptor axon projects within a single column to a specific layer of the optic lobe. We refer to the restriction of terminals to single columns as tiling. In a genetic screen based on an R7-dependent behavior, we identified the Activin receptor Baboon and the nuclear import adaptor Importin-alpha3 as being required to prevent R7 axon terminals from overlapping with the terminals of R7s in neighboring columns. This tiling function requires the Baboon ligand, dActivin, the transcription factor, dSmad2, and retrograde transport from the growth cone to the R7 nucleus. We propose that dActivin is an autocrine signal that restricts R7 growth cone motility, and we demonstrate that it acts in parallel with a paracrine signal that mediates repulsion between R7 terminals.
Unit on Neuronal Connectivity, Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20817, USA.
Chun-Yuan
CY
Ting
Tory
T
Herman
Shinichi
S
Yonekura
Shuying
S
Gao
Jian
J
Wang
Mihaela
M
Serpe
Michael B
MB
O'Connor
S Lawrence
SL
Zipursky
Chi-Hon
CH
Lee
D028341:Activins / Q000502:physiology*; D000818:Animals; D001369:Axons / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D002465:Cell Movement / Q000502:physiology; D002478:Cells, Cultured; D004330:Drosophila; D020439:Growth Cones / Q000502:physiology; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D009154:Mutation / Q000502:physiology; D019899:Paracrine Communication / Q000502:physiology; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology; D017729:Presynaptic Terminals / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D051899:Smad2 Protein / Q000235:genetics / Q000502:physiology; D014466:Ultraviolet Rays; D014785:Vision, Ocular / Q000502:physiology*; D028901:alpha Karyopherins / Q000235:genetics / Q000502:physiology
D051899:Smad2 Protein; D028901:alpha Karyopherins; D028341:Activins