Robustness of Geometry Sensing

Urša Uršič

AutorIn

Urša Uršič

Titel

Robustness of Geometry Sensing

Untertitel

Centrosome Positioning in Early Development across Variable Cytoplasmic Conditions

Zitierfähige Url:

https://nbn-resolving.org/urn:nbn:de:bsz:14-qucosa2-1053407

Erstveröffentlichung

2026

Datum der Einreichung

18.12.2025

Datum der Verteidigung

05.06.2026

Abstract (EN)

Geometry sensing in cells of early embryonic development is crucial to the correct distribution of cellular elements and the positioning of the division plane, especially in large and fast-dividing embryos. Important organizing elements are microtubule asters, which guide the centrosome motion and define the mitotic spindle position. Centrosome motion arises from microtubule-mediated processes that are dependent on microtubule aster properties and affected by the rheological properties of the cytoplasm. How these physical properties of the cytoplasm affect the centering motion of the aster is unclear. In this dissertation, I investigate the robustness of cellular centering to varying cytoplasmic physical conditions, such as cytoplasmic concentration and composition. I constructed an artificial cell-like system using Xenopus laevis cycling cytoplasmic extract with artificial centrosomes, encapsulated in oil. This system repeatedly recapitulated the centering motion of the centrosome, while allowing drastic cytoplasmic perturbations. I varied the cytoplasmic concentration and found that the aster centering success was remarkably robust across a wide range of cytoplasmic concentrations (above 50%), but not robust to variability in the cytoplasmic composition if it affected the relative density of the microtubule aster. The centering success arises as an emergent property of the balance between the microtubule-mediated centering and drag forces. Theoretical and computational models reproduced the outcome of experiments and predicted a clear phase transition of the centering success at an insufficient number of microtubules or an excessive viscosity. I tested these computational findings by increasing the viscosity of the extract droplets by adding viscogens. To expand these findings to in vivo systems, I analyzed the movement of chromatin in zebrafish embryos, the structure of the microtubule aster and the viscoelastic properties of the cytoplasm. Centering velocity was 2-fold higher, the cell cycle time was shorter, and the number of microtubules and the cytoplasmic viscosity were almost an order of magnitude higher in zebrafish embryos than in the extract. The theoretical prediction of centering success in a zebrafish embryo predicts failure with this set of parameters, suggesting that centering motion in zebrafish embryos relies on a different centering mechanism, of which the robustness to cytoplasmic physical properties is yet to be explored.

Freie Schlagwörter (EN)

cleavage division, centrosome positioning, cytoplasmic material properties

Klassifikation (DDC)

570

Klassifikation (RVK)

WE 2300

GutachterIn