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First published online 12 December 2007
doi: 10.1242/dev.008920

Development 135, 343-351 (2008)
Published by The Company of Biologists 2008
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Drosophila eggshell is patterned by sequential action of feedforward and feedback loops

Nir Yakoby1,*, Jessica Lembong1,*, Trudi Schüpbach2 and Stanislav Y. Shvartsman1,{dagger}

1 Department of Chemical Engineering and Lewis-Sigler Institute for Integrative Genomics, Princeton University, NJ 08544, USA.
2 Howard Hughes Medical Institute and Department of Molecular Biology, Princeton University, NJ 08544, USA.

{dagger} Author for correspondence (e-mail: stas{at}princeton.edu)

Accepted 17 October 2007

During Drosophila oogenesis, patterning activities of the EGFR and Dpp pathways specify several subpopulations of the follicle cells that give rise to dorsal eggshell structures. The roof of dorsal eggshell appendages is formed by the follicle cells that express Broad (Br), a zinc-finger transcription factor regulated by both pathways. EGFR induces Br in the dorsal follicle cells. This inductive signal is overridden in the dorsal midline cells, which are exposed to high levels of EGFR activation, and in the anterior cells, by Dpp signaling. We show that the resulting changes in the Br pattern affect the expression of Dpp receptor thickveins (tkv), which is essential for Dpp signaling. By controlling tkv, Br controls Dpp signaling in late stages of oogenesis and, as a result, regulates its own repression in a negative-feedback loop. We synthesize these observations into a model, whereby the dynamics of Br expression are driven by the sequential action of feedforward and feedback loops. The feedforward loop controls the spatial pattern of Br expression, while the feedback loop modulates this pattern in time. This mechanism demonstrates how complex patterns of gene expression can emerge from simple inputs, through the interaction of regulatory network motifs.

Key words: Cell signaling, Epithelial patterning, Feedforward control, Pattern formation, Drosophila


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