Topological defects control collective dynamics in neural progenitor cell cultures

Abstract

Cultured stem cells have become a standard platform not only for regenerative medicine and developmental biology but also for biophysical studies. Yet, the characterization of cultured stem cells at the level of morphology and of the macroscopic patterns resulting from cell-to-cell interactions remains largely qualitative. Here we report on the collective dynamics of cultured murine neural progenitor cells (NPCs), which are multipotent stem cells that give rise to cells in the central nervous system. At low densities, NPCs moved randomly in an amoeba-like fashion. However, NPCs at high density elongated and aligned their shapes with one another, gliding at relatively high velocities. Although the direction of motion of individual cells reversed stochastically along the axes of alignment, the cells were capable of forming an aligned pattern up to length scales similar to that of the migratory stream observed in the adult brain. The two-dimensional order of alignment within the culture showed a liquid-crystalline pattern containing interspersed topological defects with winding numbers of +1/2 and -1/2 (half-integer due to the nematic feature that arises from the head-tail symmetry of cell-to-cell interaction). We identified rapid cell accumulation at +1/2 defects and the formation of three-dimensional mounds. Imaging at the single-cell level around the defects allowed us to quantify the velocity field and the evolving cell density; cells not only concentrate at +1/2 defects, but also escape from -1/2 defects. We propose a generic mechanism for the instability in cell density around the defects that arises from the interplay between the anisotropic friction and the active force field.

Topological Defects in a Living Nematic Ensnare Swimming Bacteria

“…The related phenomenon also occurs in other active systems, e.g., in tissue formed by cultured stem cells [49]. Topological defects in liquid crystals form whenever the system is confined, even in equilibrium, thanks to the surface anchoring of the director and nontrivial Euler characteristic of any closed surface (except a torus).…”

Tunable Dynamic Topological Defect Pattern Formation in Nematic Liquid Crystals

“…Fabrication technologies that enable the control of multifunctional patterns in materials have emerged as key drivers in the interdisciplinary research fields at the interface of material science, bioscience, optics, photonics, and physics. [1][2][3][4] Arrays of topological defects in liquid crystals (LCs) are promising candidates for the creation of such patterns, with the additional benefit of their tunability. [5][6][7] In nature, topological defects exist in a variety of physical systems such as magnets and superconductors, and they are crucial to determining materials' physical properties.…”

Low-noise phase of a two-dimensional active nematic system

“…Unlike its polar counterpart, where the appearance of macroscopic polar order results in collective directed motion or flocking [3,4], the active nematic involves driven apolar constituents, which means on average the system goes nowhere [5] making its properties far more subtle. Examples of active nematics include monolayers of melanocytes [6,7], fibroblasts [8], neural progenitors [9], myxobacteria [10,11], swimming filamentous bacteria [12][13][14], vibrated rods [15] and microtubule-kinesin suspensions [16].…”