Dependence of Drosophila wing imaginal disc cytonemes on decapentaplegic

The anterior/ posterior ( A/ P) and dorsal/ ventral ( D/ V) compartment borders that subdivide the wing imaginal discs of Drosophila third instar larvae are each associated with a developmental organizer. Decapentaplegic ( Dpp), a member of the transforming growth factor-beta ( TGF-beta) superfamily, embodies the activity of the A/ P organizer. It is produced at the A/ P organizer and distributes in a gradient of decreasing concentration to regulate target genes, functioning non- autonomously to regulate growth and patterning of both the anterior and posterior compartments(1 - 3). Wingless ( Wg) is produced at the D/ V organizer and embodies its activity(4,5). The mechanisms that distribute Dpp and Wg are not known, but proposed mechanisms include extracellular diffusion(6), successive transfers between neighbouring cells(7,8), vesicle- mediated movement(9), and direct transfer via cytonemes(10). Cytonemes are actin-based filopodial extensions that have been found to orient towards the A/ P organizer from outlying cells. Here we show that in the wing disc, cytonemes orient towards both the A/ P and D/ V organizers, and that their presence and orientation correlates with Dpp signalling. We also show that the Dpp receptor, Thickveins ( Tkv), is present in punctae that move along cytonemes. These observations are consistent with a role for cytonemes in signal transduction.