Abstract
Metazoan Hedgehog (Hh) morphogens are essential regulators of growth and patterning at significant distances from their source, despite being produced as N-terminally palmitoylated and C-terminally cholesteroylated proteins, which firmly tethers them to the outer plasma membrane leaflet of producing cells and limits their spread. One mechanism to overcome this limitation is proteolytic processing of both lipidated terminal peptides, called shedding, but molecular target site requirements for effective Hh shedding remained undefined. In this work, by using Drosophila melanogaster as a model, we show that mutagenesis of the N-terminal Cardin-Weintraub (CW) motif inactivates recombinant Hh proteins to variable degrees and, if overexpressed in the same compartment, converts them into suppressors of endogenous Hh function. In vivo, additional removal of N-palmitate membrane anchors largely restored endogenous Hh function, supporting the hypothesis that proteolytic CW processing controls Hh solubilization. Importantly, we also observed that CW repositioning impairs anterior/posterior compartmental boundary maintenance in the third instar wing disc. This demonstrates that Hh shedding not only controls the differentiation of anterior cells, but also maintains the sharp physical segregation between these receiving cells and posterior Hh-producing cells.