Hexanematic crossover in epithelial monolayers depends on cell adhesion and cell density

Abstract

During tissue folding in developmental processes and monolayer migration in wound healing, epithelial cells undergo shape changes and move collectively. Recent experimental and numerical results suggested that these processes could leverage on the existence of both nematic (2--fold) and hexatic (6--fold) orientational order coexisting at different length scales within the same epithelial layer. Yet, how this remarkable example of multiscale organization in living matter is affected by the material properties of the cells and their substrate is presently unknown. In the current article, we experimentally address these questions in monolayers of Madin-Darby canine kidney cells (MDCK-II) having various cell density and molecular repertoire. At small length scales, confluent monolayers are characterized by a prominent hexatic order and nearly vanishing nematic order, independently on the presence of E-cadherin, the monolayer density, and the underlying substrate stiffness. All three properties, however, dramatically affect the organization of MDCK-II monolayers at large length scales, where nematic order becomes dominant over hexatic order. In particular, we find that the length scale at which nematic order prevails over hexatic order -- here referred to as hexanematic crossover scale -- strongly depends on cell-cell adhesions and correlates with the monolayer density. Our analysis sheds light on how the organization of epithelial layers is affected by the material and mechanical properties, and provides a robust approach for analyzing the tissue composition towards understanding developmental processes.

Emergence of bidirectional cell laning from collective contact guidance

“…However, previous experiments conducted on unpatterned substrates have concluded that HBEC monolayers could be described as a turbulent active nematic phase with half-integer topological defects 5 . To reconcile these seemingly contradictory findings, we analyzed how the local order scaled with the size 𝑅 of the window over which this order parameter was computed 44 (see Supplementary Notes 5.7). For randomly oriented 𝑁 particles, the order parameter scales as 1 √𝑁 as a consequence of the central limit theorem, and therefore as 1 𝑅 in two dimensions.…”

Interplay between mechanochemical patterning and glassy dynamics in cellular monolayers

“…in active migration force [56] or in proliferation-dependent cell size [57]). Other interesting directions would be to incorporate the effect of active nematics and turbulence [58][59][60][61][62] or to consider alternative theoretical modes of mechano-sensitive couplings which have been recently proposed, for instance on junctional tensions driving active cell rearrangements [34] or junction remodelling [34,63,64]. Finally, while we have considered a minimal model of ERK dynamics and its coupling to mechanics, considering more complex features of the pathway such as activator-inhibitor dynamics [65] would be an important next step.…”