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First published online 26 January 2006
doi: 10.1242/dev.02253
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1 Laboratory of Pattern Formation, Institute of Molecular and Cellular
Biosciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-0032,
Japan.
2 Graduate Program in Biophysics and Biochemistry, Graduate School of Science,
The University of Tokyo, Hongo7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan.
* Author for correspondence (e-mail: ttabata{at}iam.u-tokyo.ac.jp)
Accepted 15 December 2005
During development of the Drosophila visual center, photoreceptor cells extend their axons (R axons) to the lamina ganglion layer, and trigger proliferation and differentiation of synaptic partners (lamina neurons) by delivering the inductive signal Hedgehog (Hh). This inductive mechanism helps to establish an orderly arrangement of connections between the R axons and lamina neurons, termed a retinotopic map because it results in positioning the lamina neurons in close vicinity to the corresponding R axons. We found that the bHLH-PAS transcription factor Single-minded (Sim) is induced by Hh in the lamina neurons and is required for the association of lamina neurons with R axons. In sim mutant brains, lamina neurons undergo the first step of differentiation but fail to associate with R axons. As a result, lamina neurons are set aside from R axons. The data reveal a novel mechanism for regulation of the interaction between axons and neuronal cell bodies that establishes precise neuronal networks.
Key words: Visual system, Lamina, Postsynaptic neuron, sim, hh, Drosophila
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