2026-10-13T11:48:20Z https://api.figshare.com/v2/oai

oai:figshare.com:article/33977218 2026-09-23T17:53:03Z category_1 category_915 category_12 category_13 category_16 category_24 category_734 category_61 portal_5 item_type_2 month_year_09_2026

<p>Membrane cross-section during polarization.</p> Michiel Vanslambrouck (11447440) Jef Vangheel (10944795) Ella Linxia Müller (20995764) Bart Smeets (170582) Pierre Gönczy (434319) Rob Jelier (51741) Biophysics Physical Sciences not elsewhere classified Cell Biology Genetics Physiology Evolutionary Biology Biological Sciences not elsewhere classified Developmental Biology stiff contractile filaments nematic structures contribute high spatiotemporal resolution enables par proteins embryo midpoint emerges div >< p contractile nematic structures biochemical mechanisms maintaining approximately 30 min symmetry breaks near domain arrest near cortical material redistribution robust zygotic polarization polarization remains unclear mechanical negative feedback symmetry breaking occurs posterior domain towards dependent contractility regulation asymmetric cell division measured cortical flow tracking myosin foci presumptive posterior pole complete polarization process symmetry breaking cortical flow myosin foci posterior tension domain stabilization cortical architecture anterior domain mechanical role flow direction flow creates mechanical model well understood tension anisotropy surface ruffles posterior domains nearest pole local downregulation establish anterior elegans </ contributed centrosomes balances anterior anisotropic tension actin bundles <div><p>The <i>C. elegans</i> zygote is a powerful model for asymmetric cell division. Its strikingly patterned cortex features thick F-actin bundles and myosin foci, contractile nematic structures that drive characteristic surface ruffles. Approximately 30 min after fertilization, symmetry breaks near the sperm-contributed centrosomes, typically at the presumptive posterior pole, and is marked by local downregulation of contractility. This initiates a cortical flow that polarizes the cell and enables PAR proteins to establish anterior and posterior domains. While biochemical mechanisms maintaining these domains are well understood, the mechanical role of cortical architecture in polarization remains unclear. We developed a three-dimensional (3D) mechanical model of <i>C. elegans</i> zygote polarization that represents the actin bundles and myosin foci of the cortex as a network of stiff contractile filaments. We measured cortical flow with high spatiotemporal resolution by tracking myosin foci, and used these data alongside mechanical properties from the literature to parametrize the model. The model simulates the complete polarization process in 3D, from symmetry breaking through domain stabilization, and reproduces key cortical dynamics including flow profiles, surface ruffles, and tension anisotropy. Domain arrest near the embryo midpoint emerges from density-dependent contractility regulation, in which cortical material redistribution during flow creates a mechanical negative feedback that balances anterior and posterior tension. We find that compressive flow aligns actin bundles in the anterior domain and generates anisotropic tension perpendicular to the flow direction. Although this alignment is not essential for polarization when symmetry breaking occurs at the pole, it contributes to this process when symmetry breaking occurs laterally. In such cases, anisotropic tension from aligned bundles drives axis convergence by rotating the posterior domain towards the nearest pole. Nematic cortical structures therefore ensure robust alignment of the polarization axis.</p></div> 2026-09-23T17:59:22Z Dataset Media 10.1371/journal.pcbi.1014792.s007 https://figshare.com/articles/media/_p_Membrane_cross-section_during_polarization_p_/33977218 CC BY 4.0