Cell Division and Motility Enable Hexatic Order in Biological Tissues

Area of Science:

• Biophysics
• Cellular Dynamics
• Soft Matter Physics

Background:

• Biological tissues exhibit solid-like and liquid-like states crucial for physiological processes.
• Two-dimensional epithelial tissues may transition through hexatic phases, similar to 2D melting, characterized by orientational order without translational order.
• Previous research identified motility and thermal fluctuations as inducers of hexatic order, but the role of cell division and apoptosis was unclear.

Purpose of the Study:

• To investigate the impact of cell division and apoptosis on global hexatic order in biological tissues.
• To understand the interplay between cell division, apoptosis, and active motility in tissue phase transitions.

Main Methods:

• Utilized the self-propelled Voronoi model to simulate tissue dynamics.
• Analyzed the effects of varying cell division, apoptosis rates, and active motility.
• Developed a mean-field model to explain the observed competition and order development.

Main Results:

• Demonstrated that the combination of cell division and active motility induces a liquid-hexatic-liquid transformation as motility increases.
• Identified that the hexatic phase emerges from a balance between dislocation defects generated by cell division and active binding of disclination-antidisclination pairs driven by motility.
• Showcased that cell division, while seemingly disruptive, is essential for accessing the hexatic phase under active conditions.

Conclusions:

• Cell division and apoptosis play a significant, previously underestimated role in regulating tissue phase transitions.
• The interplay between cell birth/death and active cell motility governs the emergence and stability of hexatic order in tissues.
• Findings provide a mechanistic understanding of how fundamental cellular processes contribute to tissue-level emergent behavior.