{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"ae913471378684424effedbd143425e7a317532adc1ab4bdfe98cd6dff1a47ae","created":"2026-10-03T07:17:57Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"fd031f27300b31aea88abaf9e2fc074b5c47fd0074d3d8909fa2d7f65ceffc6d","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"bio.morphogenesis-mechanics.gradient-scaling","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"The signaling molecule Dpp forms a concentration gradient across the fly wing, and its decay length grows in proportion to the wing as it grows. Which chemistry keeps this proportion is disputed.","posed_since":"2011","precise":"In the Drosophila wing disc, the Dpp gradient decay length $\\lambda$ scales with disc length $L$ during growth, $\\lambda/L \\sim \\mathrm{constant}$ (Wartlick and co-workers, 2011). Identify which parameter in $\\lambda = \\sqrt{D/k}$ ($D$ = effective diffusion constant, $k$ = degradation rate) is regulated and by which feedback (expander-repressor via Pentagone, intracellular recycling of Dpp, dilution by growth, receptor regulation), with a model that predicts $\\lambda(L)$ in mutants.","problem_ref":null,"references":"","settled_by":"Measurement of $D$ and $k$ versus disc size in wild type and feedback mutants, showing which one changes to keep $\\lambda / L$ fixed.","status_note":"","title":"Mechanism of morphogen gradient scaling in growing 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