Active morphogenesis of patterned epithelial shells.

Area of Science:

• Biophysics
• Developmental Biology
• Cellular Mechanics

Background:

• Epithelial tissue morphogenesis is vital for embryonic development and organoid formation.
• Cellular cytoskeleton generates active forces driving tissue shape transformations.
• The relationship between local forces, tissue geometry, and macroscopic morphogenesis is not fully understood.

Purpose of the Study:

• To model epithelial sheets as active viscoelastic surfaces to understand tissue-scale morphogenesis.
• To investigate how patterned internal tensions, bending moments, and nematic alignment influence tissue deformation.
• To identify the mechanical principles underlying fundamental morphogenetic processes.

Main Methods:

• Developed a theoretical framework describing epithelial sheets as active viscoelastic surfaces.
• Incorporated isotropic and nematic (in-plane alignment) effects on active tensions and bending moments.
• Analyzed deformation of closed shells under patterned internal forces and moments, presenting phase diagrams and exploring dynamics.

Main Results:

• Demonstrated that nematic alignment combined with gradients in tension and bending moments can induce anisotropic active stresses.
• Identified specific combinations of forces and moments sufficient to generate key morphogenetic events.
• Phase diagrams revealed distinct mechanical equilibrium shapes and dynamic deformation pathways.

Conclusions:

• A combination of nematic alignment and gradients in internal tensions and bending moments is sufficient to drive epithelial morphogenesis.
• The model successfully reproduces fundamental morphogenetic building blocks, including folding, budding, flattening, and tubulation.
• Provides a mechanical framework for understanding how active cellular forces translate into tissue-scale shape changes.