Elastic properties of nematoid arrangements formed by amoeboid cells

Abstract

In culture migrating and interacting amoeboid cells can form nematoid arrangements in analogy to a nematic liquid crystal phase. A nematoid arrangement is formed if the interaction has an apolar symmetry. Different cell types like human melanocytes (= pigment cells of the skin), human fibroblasts (= connective tissue cells), human osteoblasts (= bone cells), human adipocytes (= fat cells) etc., form a nematoid structure. Our hypothesis is that elastic properties of these nematoid structures can be described in analogy to that of classical nematic liquid crystals. The orientational elastic energy is derived and the orientational defects (disclination) of nematoid arrangements are investigated. The existence of halfnumbered disclinations shows that the nematoid structure has an apolar symmetry. The density-and order parameter dependence of the orientational elastic constants and their absolute values are estimated. From the defect structure, one finds that the splay elastic constant is smaller than the bend elastic constant (melanocytes). The core of a disclination is either a cell free space or occupied by non oriented cells (isotropic state), by a cell with a different symmetry, or by another cell type.

Force-induced cell polarisation is linked to RhoA-driven microtubule-independent focal-adhesion sliding

“…S7A) a self-developed software macro embedded in ImageJ (http://rsb.info.nih.gov/ij/) was used. Subareas of a cell were analysed by texture analysis via a fast Fourier transformation (FFT) in analogy to Kemkemer et al (Kemkemer et al, 2000). In brief, each cell picture was divided into many small squares (64ϫ64 pixels).…”

Increased noise as an effect of haploinsufficiency of the tumor-suppressor gene neurofibromatosis type 1 in vitro

“…The selfadjustment to a set point is the mechanism that prevents the cell from becoming disordered, and therefore this mechanism is also called self-regulation (34). This concept has been successfully applied to describe the directed migration of granulocytes as related to various input signals (35)(36)(37), the orientation of fibroblasts (8) or keratinocytes (38), and the self-organized alignment of interacting melanocytes in vitro (39,40). The ratios of the parameters of the mathematical model, represented by signal-to-noise ratios, were determined from the experimental data, and we checked how well the model describes the measured data by using a fitting algorithm.…”

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].…”