Periodic Reporting for period 4 - NanoMechShape (Molecular control of actin network architecture and mechanics during cell shape changes)
Période du rapport: 2023-11-01 au 2025-04-30
All the cells in our body come from an initial spherical cell, the fertilised egg. As the embryo develops and its cells differentiate, they acquire distinct shapes. These shapes are part of a cell’s identity, are central to cellular function, and cell shape deregulation is at the heart of many pathologies including cancer. It is thus essential to understand how cell morphology is controlled in physiological and pathological conditions.
Understanding cell shape is a question at the interface of physics and biology. Indeed, cell morphology is the net result of mechanical forces acting on the cell membrane, both from the outside, through interaction with the environment, and from the inside, where the cellular cytoskeletal networks can push and pull on the membrane. Understanding cell shape control thus requires studies integrating biology with physics. The NanoMechShape project takes such a cross-disciplinary approach to investigate the regulation of animal cell shape.
In animal cells, intracellular forces controlling cell shape are mostly exerted by networks of actin and myosin, the same proteins that generate contractility in muscle cells. In non-muscle cells, they form networks supporting the cellular membrane and, by pushing and pulling on the membrane, drive cell deformations. The NanoMechShape focused on 3 core objectives:
1. To explore how the nanoscale organisation of cellular acto-myosin networks controls the mechanical properties of these networks.
2. To investigate how this nanoscale organisation changes to generate local forces driving cell division, where a cell forms a cleavage furrow to cut itself into two.
3. To understand how acto-myosin networks are reorganised when cells transition from rounded shapes towards spread shapes during cellular state changes.
Over the course of the project, we identified key molecular principles by which nanoscale interactions between actin and myosin regulate cell mechanics and cell shape change. We discovered that membrane tension in particular acts as a key signal controlling feedbacks between cell shape and cell state. Finally, we developed innovative imaging and computational tools to quantify cell-shape dynamics, and used them to uncover basic physical principles driving cell shape change. Together, these results establish a new multiscale understanding of how nanoscale organisation of cellular components determines cell mechanics, linking nanoscale structures to cell-scale behaviour.
Understanding cell shape is a question at the interface of physics and biology. Indeed, cell morphology is the net result of mechanical forces acting on the cell membrane, both from the outside, through interaction with the environment, and from the inside, where the cellular cytoskeletal networks can push and pull on the membrane. Understanding cell shape control thus requires studies integrating biology with physics. The NanoMechShape project takes such a cross-disciplinary approach to investigate the regulation of animal cell shape.
In animal cells, intracellular forces controlling cell shape are mostly exerted by networks of actin and myosin, the same proteins that generate contractility in muscle cells. In non-muscle cells, they form networks supporting the cellular membrane and, by pushing and pulling on the membrane, drive cell deformations. The NanoMechShape focused on 3 core objectives:
1. To explore how the nanoscale organisation of cellular acto-myosin networks controls the mechanical properties of these networks.
2. To investigate how this nanoscale organisation changes to generate local forces driving cell division, where a cell forms a cleavage furrow to cut itself into two.
3. To understand how acto-myosin networks are reorganised when cells transition from rounded shapes towards spread shapes during cellular state changes.
Over the course of the project, we identified key molecular principles by which nanoscale interactions between actin and myosin regulate cell mechanics and cell shape change. We discovered that membrane tension in particular acts as a key signal controlling feedbacks between cell shape and cell state. Finally, we developed innovative imaging and computational tools to quantify cell-shape dynamics, and used them to uncover basic physical principles driving cell shape change. Together, these results establish a new multiscale understanding of how nanoscale organisation of cellular components determines cell mechanics, linking nanoscale structures to cell-scale behaviour.
Throughout the project, the NanoMechShape team combined cell biology, advanced microscopy, computational analysis and physical modelling to investigate how cells control the mechanical properties of their surface and drive cell shape changes.
Key achievements and findings:
• Visualising the cell cortex at the nanoscale: Using state-of-the-art super-resolution microscopy, we unveiled how nanoscale interactions between myosin motors and cortical actin networks determine the mechanical properties of the cell surface (Truong Quang, Peters et al., Nature Communications 2021).
• Mapping the molecular composition of the cortex: We conducted large-scale proteomic analysis to identify the most abundant structural proteins of the actin cortex and revealed an unexpected role for septins in regulating cell shape during division (Vadnjal et al., J Cell Science 2022)
• Linking membrane mechanics to stem-cell fate: We discovered that changes in plasma-membrane tension act as a key signal controlling differentiation in mouse embryonic stem cells. This demonstrated direct mechanosensing feedback between cell surface mechanics and instructive signalling driving differentiation (De Belly et al., Cell Stem Cell 2021).
• Developing morphospace analysis: We created a computational analysis pipeline that represents cell-shape dynamics in a reduced mathematical space (“morphospace”). Combining morphospace analysis with stochastic modelling unveiled key physical principles controlling cell shape change (Pönisch, Yanakieva et al., bioRxiv 2024).
• Quantifying actin organisation with novel tools: We applied cryo-electron tomography and advanced polarisation microscopy to obtain advanced quantitative descriptions of nanoscale actin network architectures (Cassani et al., bioRxiv 2024; Bruggeman et al., Nature Methods 2024).
Dissemination and impact: Results were shared through publications, invited talks, conference presentations and open-data repositories. All software generated through the project is made freely available through the group’s Github. As a result, the methodologies and concepts developed in NanoMechShape will be widely transferable to other biological questions where cell shape changes are key. As such, they will inform studies of development, tissue mechanics, and disease progression.
Key achievements and findings:
• Visualising the cell cortex at the nanoscale: Using state-of-the-art super-resolution microscopy, we unveiled how nanoscale interactions between myosin motors and cortical actin networks determine the mechanical properties of the cell surface (Truong Quang, Peters et al., Nature Communications 2021).
• Mapping the molecular composition of the cortex: We conducted large-scale proteomic analysis to identify the most abundant structural proteins of the actin cortex and revealed an unexpected role for septins in regulating cell shape during division (Vadnjal et al., J Cell Science 2022)
• Linking membrane mechanics to stem-cell fate: We discovered that changes in plasma-membrane tension act as a key signal controlling differentiation in mouse embryonic stem cells. This demonstrated direct mechanosensing feedback between cell surface mechanics and instructive signalling driving differentiation (De Belly et al., Cell Stem Cell 2021).
• Developing morphospace analysis: We created a computational analysis pipeline that represents cell-shape dynamics in a reduced mathematical space (“morphospace”). Combining morphospace analysis with stochastic modelling unveiled key physical principles controlling cell shape change (Pönisch, Yanakieva et al., bioRxiv 2024).
• Quantifying actin organisation with novel tools: We applied cryo-electron tomography and advanced polarisation microscopy to obtain advanced quantitative descriptions of nanoscale actin network architectures (Cassani et al., bioRxiv 2024; Bruggeman et al., Nature Methods 2024).
Dissemination and impact: Results were shared through publications, invited talks, conference presentations and open-data repositories. All software generated through the project is made freely available through the group’s Github. As a result, the methodologies and concepts developed in NanoMechShape will be widely transferable to other biological questions where cell shape changes are key. As such, they will inform studies of development, tissue mechanics, and disease progression.
• Technical pipeline to investigate the nanoscale architecture of the cell cortex: The actin cortex, which determines cell surface mechanics and cell shape, is notoriously difficult to study because it is very dense and thin, and thus challenging to image. We developed a panel of techniques using state of the art microscopy techniques (super-resolution, polarisation and electron microscopy) that provide unprecedented insight into how the cellular scaffold supporting the cell surface is built and organised.
• Revealing how nanoscale interactions controls cell surface mechanics: By applying our imaging pipelines, we demonstrated that the physical size and arrangement of molecular myosin motors directly determine cortical tension.
• Mechanical signalling in cell fate control: Cellular differentiation is still mostly studied with a focus on the molecular signals that control it. We uncovered that changes in membrane tension, a key physical property of the cell surface, act as mechanical signal directly guiding stem cell differentiation.
• Developing new tools to quantify cell-shape dynamics: We developed a “morphospace” analysis framework where cell shape is quantified with a degree of precision usually only accessible in -omics studies of molecular data. We combine this with a stochastic analysis framework to understand how cells change shape.
• Revealing how nanoscale interactions controls cell surface mechanics: By applying our imaging pipelines, we demonstrated that the physical size and arrangement of molecular myosin motors directly determine cortical tension.
• Mechanical signalling in cell fate control: Cellular differentiation is still mostly studied with a focus on the molecular signals that control it. We uncovered that changes in membrane tension, a key physical property of the cell surface, act as mechanical signal directly guiding stem cell differentiation.
• Developing new tools to quantify cell-shape dynamics: We developed a “morphospace” analysis framework where cell shape is quantified with a degree of precision usually only accessible in -omics studies of molecular data. We combine this with a stochastic analysis framework to understand how cells change shape.