A Geometric-tension-dynamics Model of Epithelial Convergent Extension.

Area of Science:

• Developmental Biology
• Biophysics
• Computational Biology

Background:

• Convergent extension is crucial for animal morphogenesis, involving epithelial tissue movement.
• Epithelial cells maintain tissue integrity via internal tension, unlike fluid dynamics.
• The mechanism balancing cell adhesion and tissue flow under tension remains unclear.

Purpose of the Study:

• To model epithelial tissue flow in a tension-dominated regime.
• To investigate the role of cytoskeletal tension and cell rearrangements (T1 transitions) in morphogenesis.
• To understand how initial cellular packing influences tissue deformation.

Main Methods:

• Formulation of a biophysical model for tissue flow based on force balance in adherens junctions.
• Analysis of adiabatic remodeling of force balance driven by myosin-generated cytoskeletal tension.
• Quantification of tension configurations using a geometric order parameter.

Main Results:

• Tissue flow occurs through remodeling of force balance, driven by positive feedback on cytoskeletal tension.
• Active cell rearrangements (T1 transitions) are triggered by shifting force balance, orienting tissue deformation.
• Total tissue deformation is limited by initial cellular packing order, as T1 transitions degrade order.

Conclusions:

• Coordination of cell rearrangements depends on local tension configurations and their geometric order.
• The model accurately reproduces key features of Drosophila germ band elongation, including flow slowdown.
• Local cell geometry and active tension dynamics are critical for understanding morphogenetic flow.