Shaping and interpretation of Dpp morphogen gradient by endocytic trafficking

Area of Science:

• Developmental Biology
• Cell Biology
• Molecular Biology

Background:

• Decapentaplegic (Dpp)/Bone Morphogenetic Protein (BMP) is a key morphogen regulating Drosophila wing disc patterning and growth.
• Endocytic trafficking's role in Dpp gradient formation and signaling interpretation remains incompletely understood due to visualization challenges.

Purpose of the Study:

• To investigate the precise roles of endocytic trafficking pathways in shaping and interpreting the Dpp gradient in Drosophila wing discs.
• To visualize endogenous Dpp distribution and signaling dynamics using novel fluorescently tagged alleles.

Main Methods:

• Generation of fluorescent protein-tagged functional dpp alleles for simultaneous visualization of extracellular and intracellular Dpp.
• Analysis of Dpp signaling dynamics and gradient formation under conditions of inhibited endocytic trafficking (Dynamin, Rab5, MVB formation).

Main Results:

• Dynamin-mediated internalization is essential for Dpp signaling activation.
• Rab5-mediated early endosomal trafficking is dispensable for Dpp spreading and initiation but crucial for signal termination via receptor downregulation.
• Dpp signaling termination occurs at multivesicular bodies (MVBs) via ESCRT-dependent sorting, not lysosomal degradation.
• Inhibition of MVB formation expands the Dpp signaling gradient, impairing gradient interpretation without affecting extracellular Dpp levels.

Conclusions:

• The extracellular Dpp gradient is established by Dynamin-dependent internalization.
• Intracellular signaling duration, regulated by MVB-mediated receptor sorting, is critical for interpreting the Dpp gradient.
• Endocytic trafficking plays a dual role in both shaping and interpreting morphogen gradients during development.