Birth order dependent growth cone segregation determines synaptic layer identity in the Drosophila visual system

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Abstract

The precise recognition of appropriate synaptic partner neurons is a critical step during neural circuit assembly. However, little is known about the developmental context in which recognition specificity is important to establish synaptic contacts. We show that in the Drosophila visual system, sequential segregation of photoreceptor afferents, reflecting their birth order, lead to differential positioning of their growth cones in the early target region. By combining loss- and gain-of-function analyses we demonstrate that relative differences in the expression of the transcription factor Sequoia regulate R cell growth cone segregation. This initial growth cone positioning is consolidated via cell-adhesion molecule Capricious in R8 axons. Further, we show that the initial growth cone positioning determines synaptic layer selection through proximity-based axon-target interactions. Taken together, we demonstrate that birth order dependent pre-patterning of afferent growth cones is an essential pre-requisite for the identification of synaptic partner neurons during visual map formation in Drosophila.

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Abhishek Kulkarni

Department of Neurobiology, University of Vienna, Vienna, Austria

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The authors declare that no competing interests exist.
Deniz Ertekin

Department of Neurobiology, University of Vienna, Vienna, Austria

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The authors declare that no competing interests exist.
Chi-Hon Lee

Section on Neuronal Connectivity, Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, United States

Competing interests
The authors declare that no competing interests exist.
Thomas Hummel

Department of Neurobiology, University of Vienna, Vienna, Austria

For correspondence
thomas.hummel@univie.ac.at

Competing interests
The authors declare that no competing interests exist.

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