The pronotum LIM-HD gene tailup is both a positive and a negative regulator of the proneural genes achaete and scute of Drosophila
In Drosophila, the GATA family transcription factor Pannier and the Wnt secreted protein Wingless are known to be important for the patterning of the notum, a part of the dorsal mesothorax of the fly. Thus, both proteins are necessary for the development of the dorsocentral mechanosensory bristles, although their roles in this process have not been clarified. Here, we show that Pannier directly activates the proneural genes achaete and scute by binding to the enhancer responsible for the expression of these genes in the dorsocentral proneural cluster. Moreover, the boundary of the expression domain of Pannier appears to delimit the proneural cluster laterally, while antagonism of Pannier function by the Zn-finger protein U-shaped sets its limit dorsally. So, Pannier and U-shaped provide positional information for the patterning of the dorsocentral cluster. In contrast and contrary to previous suggestions, Wingless does not play a similar role, since the levels and vectorial orientation of its concentration gradient in the dorsocentral area can be greatly modified without affecting the position of the dorsocentral cluster. Thus, Wingless has only a permissive role on dorsocentral achaete-scute expression. We also provide evidence indicating that Pannier and U-shaped are main effectors of the regulation of wingless expression in the presumptive notum.