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bioRxiv · 10.1101/2025.11.21.688964

Steady-state epithelial apical flatness is characterized by MLCK morphodynamics and asynchronous Ca2+ oscillations, but not underlying ECM geometry

Wu, H.·Herrmann, E. G.·Hyer, J. M.·Hua, L. L.·Mikawa, T.
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Abstract

The canonical simple epithelium is a flat sheet-like tissue of horizontally packed cells. While the basal surface is delineated by the basement membrane of extracellular matrix (ECM), little is known about how a flat apical surface is maintained, or if apical/basal dynamics are coordinated. The current study tests the role of the apical domain, to define mechanisms involved in maintaining a flat apical geometry in an epithelium. When the basal geometry is modulated, Madin-Darby Canine Kidney (MDCK) cells adjust their morphology to maintain an overall apical flatness of the confluent layer. Pharmacological and transgenic disruption of non-muscle myosin ATPase, and MLCK activity results in an uneven apical structure, and overall loss of the flat geometry typical of a confluent epithelium. Surprisingly, transgenic experimentation showed that forces maintaining individual MDCK cell flatness are cell-autonomous. Finally, Ca2+ imaging reveals an asynchronous calcium flux across a confluent epithelium, suggesting a myosin II-mediated mechanism for maintaining a flat apical architecture. Our results highlight that apical/basal cellular surfaces may not be tightly coordinated, but rather independently regulated. This study provides a new paradigm for how apical flatness is regulated at steady state. Impact StatementO_LIHow surface flatness of an epithelium is established and maintained is unknown; the data reveal that apical flatness is controlled independently from basement membrane geometry, and require balancing of myosin II morphodynamics. C_LI

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Wu, H., Herrmann, E. G., Hyer, J. M., Hua, L. L., Mikawa, T.. 2025-11-25. Steady-state epithelial apical flatness is characterized by MLCK morphodynamics and asynchronous Ca2+ oscillations, but not underlying ECM geometry. https://doi.org/10.1101/2025.11.21.688964

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