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Mechanics and Architecture of the Cellular Actomyosin Cortex

Cassani, Davide Ariberto Domenico; (2019) Mechanics and Architecture of the Cellular Actomyosin Cortex. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Cell shape changes are key to cell physiology and underlie fundamental processes such as cell migration, cell division and tissue morphogenesis. Cell shape changes are precisely controlled by cell surface mechanics. One of the main determinant of cell surface mechanics is the actomyosin cortex, a thin network of actin, myosin and actin associated proteins underlying the plasma membrane. Cortex mechanical properties are not determined only by the cortical network composition but also by its nano-scale architecture. Although previous studies have shown a relationship between cortex organization and mechanics, which aspects of cortex architecture contribute to the regulation of cell surface mechanics remain largely unknown. This gap in understanding is mostly due to the small dimensions of the cortex, with a thickness close to the diffraction limit of light microscopy, which makes the investigation of cortical nanoscale organization challenging. In my PhD, I investigated cortex nano-scale organization and asked how cortex architecture affects cortex mechanics. In order to assess cortex mechanics, I established an AFM-based assay to measure cell cortex tension. By combining AFM measurements with an analysis on cortex thickness and targeted protein depletion, I demonstrated that cortical network organization directly affects cortex tension. I then further explored cortical organization focusing on nano-scale architecture. Due to the high density of the cortex, previous techniques, including super-resolution imaging, had failed to unveil actin filament organization. To assess this, I established a method to image actin filaments in the cortex using cryo electron tomography. I used isolated cellular blebs, which have been shown to repolymerise a cortex similar to that of intact cells and have dimensions compatible with cryo electron tomography. Actin cortex organization in blebs was analyzed using custom-made software and key parameters of cortical architecture were extracted. My investigation on cortex nano-scale architecture provides, to my knowledge, the first quantification of cortical actin organization and brings new insights into how cortex microscopic properties regulate the mesoscopic properties of cells.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Mechanics and Architecture of the Cellular Actomyosin Cortex
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
Keywords: Actin, biophysics, cryoem, tomography, cell mechanics, cell cortex, blebs
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Lab for Molecular Cell Bio MRC-UCL
URI: https://discovery.ucl.ac.uk/id/eprint/10066336
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