Active cell divisions generate fourfold orientationally ordered phase in living tissue.

Area of Science:

• Developmental Biology
• Cell Biology
• Biophysics

Background:

• Morphogenesis establishes tissue-scale order for body plan construction.
• Cell proliferation fuels growth but can disrupt tissue order.
• Mechanisms coupling cell division, mechanics, and order are poorly understood.

Purpose of the Study:

• Investigate how cell divisions generate tissue order during animal development.
• Understand the interplay between cell proliferation, tissue flow, and orientational order.
• Identify mechanisms that maintain tissue organization despite growth.

Main Methods:

• Live imaging of *Parhyale hawaiensis* trunk segmental ectoderm.
• Tissue cartography to analyze dynamics of orientational ordering.
• Analysis of cell division patterns and tissue flow.

Main Results:

• Cell divisions are primary drivers of tissue flow, creating a fourfold orientationally ordered phase.
• Anisotropic cell proliferation waves propagate with precise patterning.
• Division-induced defects are resolved by movement towards the tissue boundary.
• Specific proliferation rates and orientations organize, rather than fluidize, the tissue.

Conclusions:

• Cell divisions actively generate global orientational order in a non-equilibrium developmental system.
• This process provides a robust mechanism for organizing tissue structure.
• The findings set the stage for understanding subsequent shape and form development.