Patterning and growth control by membrane-tethered Wingless

Wnts are evolutionarily conserved secreted signalling proteins that, in various developmental contexts, spread from their site of synthesis to form a gradient and activate target-gene expression at a distance. However, the requirement for Wnts to spread has never been directly tested. Here we used genome engineering to replace the endogenous wingless gene, which encodes the main Drosophila Wnt, with one that expresses a membrane-tethered form of the protein. Surprisingly, the resulting flies were viable and produced normally patterned appendages of nearly the right size, albeit with a delay. We show that, in the prospective wing, prolonged wingless transcription followed by memory of earlier signalling allows persistent expression of relevant target genes. We suggest therefore that the spread of Wingless is dispensable for patterning and growth even though it probably contributes to increasing cell proliferation. Replacement of the wingless ( wg ) gene in Drosophila with one that expresses a membrane-tethered form of Wg results in viable flies with normally patterned appendages of nearly the right size; early wg transcription and memory of signalling ensure continued target-gene expression in the absence of Wg release, even though the spread of Wg could boost cell proliferation. Wingless protein's long-range signalling function Morphogens are secreted proteins with important roles in growth and patterning during development. A key feature of a morphogen is that it can act at a distance from the site of origin through a diffusion gradient. These authors have directly assessed the function of the spread of the Wingless (Wg) protein in Drosophila . They found that flies in which the resident wg gene has been replaced by an engineered form encoding a membrane-tethered Wg protein are viable and fertile. These findings are consistent with a role for Wingless as a long-range signal, but raise doubts over the essential role of a diffusion gradient.