Periodic Reporting for period 3 - NanoMechShape (Molecular control of actin network architecture and mechanics during cell shape changes)
Période du rapport: 2022-05-01 au 2023-10-31
All the cells in our body come from an initial roughly spherical cell, the fertilised egg. As an embryo develops and its cells differentiate, they acquire distinct shapes. These shapes are part of a cell’s identity, are often central to cell’s role in normal physiology, 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 underlying the plasma membrane and these networks generate pushing and pulling forces, driving cell deformations. The overall objectives of NanoMechShape are:
- To explore how the nanoscale organisation of cellular acto-myosin networks controls the mechanical properties of these networks.
- 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.
- To understand how acto-myosin networks are reorganised when cells transition from rounded shapes towards spread shapes promoting substrate interactions and cellular migration.
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 underlying the plasma membrane and these networks generate pushing and pulling forces, driving cell deformations. The overall objectives of NanoMechShape are:
- To explore how the nanoscale organisation of cellular acto-myosin networks controls the mechanical properties of these networks.
- 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.
- To understand how acto-myosin networks are reorganised when cells transition from rounded shapes towards spread shapes promoting substrate interactions and cellular migration.
Key achievements in the first half of the NanoMechShape project:
- We have investigated the cellular cortex, an actomyosin network supporting cell shape in dividing cells and controlling the physical separation of daughter cells following division. We have used state-of-the-art super-resolution microscopy to visualise how the cortex is organised at the nano-scale, and unveiled how nanoscale interactions between myosin motors and the cortical actin networks affect the mechanical properties of the cell surface mechanics (Truong Quang, Peters, et al, Nature Communications 2021).
- We have investigated the coupling between cell shape and cell fate during early differentiation of mouse embryonic stem cells. Studying mouse embryonic stem cells, we could show that early differentiation is associated with changes in cell surface mechanical properties, which lead to cell spreading. We further identified how the changes in cell mechanics lead to the activation of key signalling instructing cell differentiation (De Belly et al, Cell Stem Cell 2021).
- We have investigated the cellular cortex, an actomyosin network supporting cell shape in dividing cells and controlling the physical separation of daughter cells following division. We have used state-of-the-art super-resolution microscopy to visualise how the cortex is organised at the nano-scale, and unveiled how nanoscale interactions between myosin motors and the cortical actin networks affect the mechanical properties of the cell surface mechanics (Truong Quang, Peters, et al, Nature Communications 2021).
- We have investigated the coupling between cell shape and cell fate during early differentiation of mouse embryonic stem cells. Studying mouse embryonic stem cells, we could show that early differentiation is associated with changes in cell surface mechanical properties, which lead to cell spreading. We further identified how the changes in cell mechanics lead to the activation of key signalling instructing cell differentiation (De Belly et al, Cell Stem Cell 2021).
1. Super-resolution microscopy gives insight into the organisation of cellular structures at unprecedented resolution. Using these techniques, we could unveil how spatial stratification of proteins at a scale of tens of nanometers affects force generation in the actomyosin cortex at scales of tens of micrometers, and ultimately cell shape during cell division (Truong Quang, Peters, et al, Nature Communications 2021). In the second part of the project, we plan to push these across-scales studies further to understand how cellular forces in cell division are generated. To this aim, we will combine super-resolution imaging with advanced image analysis tools and computational modelling. This cross-disciplinary approach will allow us to bridge the gap between nanoscale interactions and cell-scale behaviours.
2. We have developed a pipeline for the automated analysis and classification of cellular shapes. Our pipeline uses machine-learning based segmentation algorithms and dimensionality reduction techniques to provide a quantitative description of any cellular shape in 2 or 3 dimensions (the pipeline is described in Bodor et al, Dev Cell 2020). In the second part of the project, we plan to use the pipeline to investigate the physical basis of shape changes during cell shape transitions associated with cellular processes such as cell division, and cellular fate changes.
2. We have developed a pipeline for the automated analysis and classification of cellular shapes. Our pipeline uses machine-learning based segmentation algorithms and dimensionality reduction techniques to provide a quantitative description of any cellular shape in 2 or 3 dimensions (the pipeline is described in Bodor et al, Dev Cell 2020). In the second part of the project, we plan to use the pipeline to investigate the physical basis of shape changes during cell shape transitions associated with cellular processes such as cell division, and cellular fate changes.