Wingless and Hedgehog pattern Drosophila denticle belts by regulating the production of short-range signals

The secreted proteins Wingless and Hedgehog are essential to the elaboratio n of the denticle pattern in the epidermis of Drosophila embryos. We show t hat signaling by Wingless and Hedgehog regulates the expression of veinlet (rhomboid) and Serrate, two genes expressed in prospective denticle belts, Thus, Serrate and veinlet (rhom) partake in the last layer of the segmentat ion cascade. Ultimately, Wingless, Hedgehog, Veinlet (an indirect activator of the Egfr) and Serrate (an activator of Notch) are expressed in non-over lapping narrow stripes. The interface between any two stripes allows a reli able prediction of individual denticle types and polarity suggesting that c ontact-dependent signaling modulates individual cell fates. Attributes of a morphogen can be ascribed to Hedgehog in this system. However, no single m orphogen organises the whole denticle pattern.