A subset of cells in the Drosophila follicular epithelium, a popular model for studying cell fate determination and morphogenesis, forms respiratory structures called dorsal appendages. Patterning within this tissue depends on Egfr signalling: dorsal appendage cell fate requires Gurken, an Egfr ligand, and Gurken-Egfr signalling is widely believed to be regulated in an autocrine feedback loop by another Egfr ligand, Spitz, and the Egfr inhibitor Argos. On , however, Laura Nilson and colleagues challenge this view by showing that the Spitz-Argos feedback loop is not required for dorsal appendage patterning and that, instead, the necessary spatial information might be provided directly by Gurken. Mirror and Pointed, two transcription factors that function downstream of Egfr signalling, and Sprouty, an Egfr signalling pathway inhibitor, they report, are crucial for this process. Together, these findings indicate that graded Gurken-Egfr signalling patterns the follicular epithelium directly rather than through an autocrine feedback loop, a notion also supported by Stanislav Shvartsman and co-workers (see ).
