Abstract
Cell-cell communication via conserved signaling pathways often involves multiple paracrine ligands that act through shared receptors and/or downstream cascades yet elicit distinct outcomes, raising the question of how specificity is achieved. In the Drosophila adult-muscle-precursor (AMP) niche, the FGF ligands Pyramus and Thisbe both signal through the Heartless (Htl) receptor in isogenic AMPs yet drive divergent responses. In-vivo imaging of endogenous Pyramus:mCherry(endo) and Thisbe:sfGFP(endo) knock-ins revealed that the ligands segregate into distinct, receptor-bound territories among isogenic AMPs. This segregation arises as AMPs acquire ligands via polarized, Htl-containing cytonemes that directly contact each ligand source. Cytoneme polarity and target-specificity are position-dependent, enabling ligand distribution to scale with tissue size and AMP organization. A positive feedback loop through the Htl-Pointed axis reinforces cytoneme polarity, amplifying ligand-specific segregation and signaling. These findings establish cell-intrinsic feedback as a general principle for sustaining cytoneme polarity and specificity, and reveal how cytonemes confer signaling specificity to pathways activated by multiple ligands within the same progenitor population.