Pattern formation during development depends on combinatorial interactions between signalling pathways, but the strategies for pathway integration and coordination are still poorly understood. Now Yakoby and colleagues have developed a new model based on network theory to explain how the Drosophila eggshell is patterned (see ). During Drosophila oogenesis, the EGFR and Dpp pathways specify the follicle cells that give rise to dorsal eggshell structures. Follicle cells that express the transcription factor Broad (Br), whose expression is regulated by both EGFR and Dpp signalling, form the roof of these structures. From their observations of signalling patterns during eggshell formation and from published data, the researchers propose that EGFR signalling determines the spatial pattern of Br by inducing the expression of both br and its transcriptional repressor Pointed (a feedforward loop). Later, a feedback loop activated by Br controls Dpp, which terminates Br expression. Future work will explore how other feedback loops interact with the simple regulatory network motifs described in this new model to generate complex gene expression patterns.
