The size of a cell is determined by a combination of synthesis, self-assembly, incoming matter and the balance of mechanical forces. Such processes operate at the single-cell level, but they are ...deeply interconnected with cell-cycle progression, resulting in a stable average cell size at the population level. Here, we examine this phenomenon by reviewing the physics of growth processes that operate at vastly different timescales, but result in the controlled production of daughter cells that are close copies of their mothers. We first review the regulatory mechanisms of size at short timescales, focusing on the contribution of fundamental physical forces. We then discuss the multiple relevant regulation processes operating on the timescale of the cell cycle. Finally, we look at how these processes interact: one of the most important challenges to date involves bridging the gap between timescales, connecting the physics of cell growth and the biology of cell-cycle progression.
Plasma membrane damage can be triggered by numerous phenomena, and efficient repair is essential for cell survival. Endocytosis, membrane patching, or extracellular budding can be used for plasma ...membrane repair. We found that endosomal sorting complex required for transport (ESCRT), involved previously in membrane budding and fission, plays a critical role in plasma membrane repair. ESCRT proteins were recruited within seconds to plasma membrane wounds. Quantitative analysis of wound closure kinetics coupled to mathematical modeling suggested that ESCRTs are involved in the repair of small wounds. Real-time imaging and correlative scanning electron microscopy (SEM) identified extracellular buds and shedding at the site of ESCRT recruitment. Thus, the repair of certain wounds is ensured by ESCRT-mediated extracellular shedding of wounded portions.
Predicting cellular behavior is a major challenge in cell and developmental biology. Since the late nineteenth century, empirical rules have been formulated to predict the position and orientation of ...mitotic cleavage planes in plant and animal cells. Here, we review the history of division plane orientation rules and discuss recent experimental and theoretical studies that refine these rules and provide mechanistic insights into how division can be predicted. We describe why some of these rules may better apply to certain cell types and developmental contexts and discuss how they could be integrated in the future to allow the prediction of division positioning in tissues.
The mesenchymal-amoeboid transition (MAT) was proposed as a mechanism for cancer cells to adapt their migration mode to their environment. While the molecular pathways involved in this transition are ...well documented, the role of the microenvironment in the MAT is still poorly understood. Here, we investigated how confinement and adhesion affect this transition. We report that, in the absence of focal adhesions and under conditions of confinement, mesenchymal cells can spontaneously switch to a fast amoeboid migration phenotype. We identified two main types of fast migration—one involving a local protrusion and a second involving a myosin-II-dependent mechanical instability of the cell cortex that leads to a global cortical flow. Interestingly, transformed cells are more prone to adopt this fast migration mode. Finally, we propose a generic model that explains migration transitions and predicts a phase diagram of migration phenotypes based on three main control parameters: confinement, adhesion, and contractility.
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•Physical confinement and low adhesion induce the mesenchymal-amoeboid transition•A large range of slow mesenchymal cell types can display fast amoeboid-like migration•A fast mode (A1) and a faster and more conserved contractile mode (A2) were observed•A2 migration could be an ancestral migratory behavior shared among eukaryotes
A large range of slow mesenchymal cells can switch to fast amoeboid-like migration under conditions of low adhesion and strong confinement, suggesting that tumor cells may spontaneously escape primary tumors and invade tissues without any specific genetic alteration.
In eukaryotic cells, the nuclear envelope separates the genomic DNA from the cytoplasmic space and regulates protein trafficking between the two compartments. This barrier is only transiently ...dissolved during mitosis. Here, we found that it also opened at high frequency in migrating mammalian cells during interphase, which allowed nuclear proteins to leak out and cytoplasmic proteins to leak in. This transient opening was caused by nuclear deformation and was rapidly repaired in an ESCRT (endosomal sorting complexes required for transport)–dependent manner. DNA double-strand breaks coincided with nuclear envelope opening events. As a consequence, survival of cells migrating through confining environments depended on efficient nuclear envelope and DNA repair machineries. Nuclear envelope opening in migrating leukocytes could have potentially important consequences for normal and pathological immune responses.
During cell growth and motility in crowded tissues or interstitial spaces, cells must integrate multiple physical and biochemical environmental inputs. After a number of recent studies, the view of ...the nucleus as a passive object that cells have to drag along has become obsolete, placing the nucleus as a central player in sensing some of these inputs. In the present review, we will focus on changes in nuclear shape caused by external and internal forces. Depending on their magnitude, nuclear deformations can generate signaling events that modulate cell behavior and fate, or be a source of perturbations or even damage, having detrimental effects on cellular functions. On very large deformations, nuclear envelope rupture events become frequent, leading to uncontrolled nucleocytoplasmic mixing and DNA damage. We will also discuss the consequences of repeated compromised nuclear integrity, which can trigger DNA surveillance mechanisms, with critical consequences to cell fate and tissue homeostasis.
Although mutations leading to a compromised nuclear envelope cause diseases such as muscular dystrophies or accelerated aging, the consequences of mechanically induced nuclear envelope ruptures are ...less known. Here, we show that nuclear envelope ruptures induce DNA damage that promotes senescence in non-transformed cells and induces an invasive phenotype in human breast cancer cells. We find that the endoplasmic reticulum (ER)-associated exonuclease TREX1 translocates into the nucleus after nuclear envelope rupture and is required to induce DNA damage. Inside the mammary duct, cellular crowding leads to nuclear envelope ruptures that generate TREX1-dependent DNA damage, thereby driving the progression of in situ carcinoma to the invasive stage. DNA damage and nuclear envelope rupture markers were also enriched at the invasive edge of human tumors. We propose that DNA damage in mechanically challenged nuclei could affect the pathophysiology of crowded tissues by modulating proliferation and extracellular matrix degradation of normal and transformed cells.
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•Deformed nuclei and DNA damage are enriched at micro-invasive foci of breast cancer•TREX1 causes DNA damage in deformed nuclei upon nuclear envelope rupture events•TREX1 drives senescence in normal cells and an invasive phenotype in cancer cells•Nuclear envelope rupture events and DNA damage are observed in human tumors
Extreme nuclear deformations in dense microenvironments lead to repeated nuclear envelope rupture followed by TREX1-dependent chronic DNA damage. This triggers a partial EMT in malignant cells which might underlie tumor progression.
The actin cytoskeleton drives many essential biological processes, from cell morphogenesis to motility. Assembly of functional actin networks requires control over the speed at which actin filaments ...grow. How this can be achieved at the high and variable levels of soluble actin subunits found in cells is unclear. Here we reconstitute assembly of mammalian, non-muscle actin filaments from physiological concentrations of profilin-actin. We discover that under these conditions, filament growth is limited by profilin dissociating from the filament end and the speed of elongation becomes insensitive to the concentration of soluble subunits. Profilin release can be directly promoted by formin actin polymerases even at saturating profilin-actin concentrations. We demonstrate that mammalian cells indeed operate at the limit to actin filament growth imposed by profilin and formins. Our results reveal how synergy between profilin and formins generates robust filament growth rates that are resilient to changes in the soluble subunit concentration.
Despite decades of research, how mammalian cell size is controlled remains unclear because of the difficulty of directly measuring growth at the single-cell level. Here we report direct measurements ...of single-cell volumes over entire cell cycles on various mammalian cell lines and primary human cells. We find that, in a majority of cell types, the volume added across the cell cycle shows little or no correlation to cell birth size, a homeostatic behavior called "adder". This behavior involves modulation of G1 or S-G2 duration and modulation of growth rate. The precise combination of these mechanisms depends on the cell type and the growth condition. We have developed a mathematical framework to compare size homeostasis in datasets ranging from bacteria to mammalian cells. This reveals that a near-adder behavior is the most common type of size control and highlights the importance of growth rate modulation to size control in mammalian cells.
The way proliferating animal cells coordinate the growth of their mass, volume, and other relevant size parameters is a long-standing question in biology. Studies focusing on cell mass have ...identified patterns of mass growth as a function of time and cell cycle phase, but little is known about volume growth. To address this question, we improved our fluorescence exclusion method of volume measurement (FXm) and obtained 1700 single-cell volume growth trajectories of HeLa cells. We find that, during most of the cell cycle, volume growth is close to exponential and proceeds at a higher rate in S-G2 than in G1. Comparing the data with a mathematical model, we establish that the cell-to-cell variability in volume growth arises from constant-amplitude fluctuations in volume steps rather than fluctuations of the underlying specific growth rate. We hypothesize that such 'additive noise' could emerge from the processes that regulate volume adaptation to biophysical cues, such as tension or osmotic pressure.
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