Cell Growth Size Research Articles

A Generalized Adder mechanism for Cell Size Homeostasis: Implications for Stochastic Dynamics of Clonal Proliferation.

Measurements of cell size dynamics have revealed phenomeno-logical principles by which individual cells control their size across diverse organisms. One of the emerging paradigms of cell size homeostasis is the adder , where the cell cycle duration is established such that the cell size increase from birth to division is independent of the newborn cell size. We provide a mechanistic formulation of the adder considering that cell size follows any arbitrary non-exponential growth law . Our results show that the main requirement to obtain an adder regardless of the growth law (the time derivative of cell size) is that cell cycle regulators are produced at a rate proportional to the growth law and cell division is triggered when these molecules reach a prescribed threshold level. Among the implications of this generalized adder, we investigate fluctuations in the proliferation of single-cell derived colonies. Considering exponential cell size growth, random fluctuations in clonal size show a transient increase and then eventually decay to zero over time (i.e., clonal populations become asymptotically more similar). In contrast, several forms of non-exponential cell size dynamics (with adder-based cell size control) yield qualitatively different results: clonal size fluctuations monotonically increase over time reaching a non-zero value. These results characterize the interplay between cell size homeostasis at the single-cell level and clonal proliferation at the population level, explaining the broad fluctuations in clonal sizes seen in barcoded human cell lines.

Improving the power of drug toxicity measurements by quantitative nuclei imaging

Imaging-based anticancer drug screens are becoming more prevalent due to development of automated fluorescent microscopes and imaging stations, as well as rapid advancements in image processing software. Automated cell imaging provides many benefits such as their ability to provide high-content data, modularity, dynamics recording and the fact that imaging is the most direct way to access cell viability and cell proliferation. However, currently most publicly available large-scale anticancer drugs screens, such as GDSC, CTRP and NCI-60, provide cell viability data measured by assays based on colorimetric or luminometric measurements of NADH or ATP levels. Although such datasets provide valuable data, it is unclear how well drug toxicity measurements can be integrated with imaging data. Here we explored the relations between drug toxicity data obtained by XTT assay, two quantitative nuclei imaging methods and trypan blue dye exclusion assay using a set of four cancer cell lines with different morphologies and 30 drugs with different mechanisms of action. We show that imaging-based approaches provide high accuracy and the differences between results obtained by different methods highly depend on drug mechanism of action. Selecting AUC metrics over IC50 or comparing data where significantly drugs reduced cell numbers noticeably improves consistency between methods. Using automated cell segmentation protocols we analyzed mitochondria activity in more than 11 thousand drug-treated cells and showed that XTT assay produces unreliable data for CDK4/6, Aurora A, VEGFR and PARP inhibitors due induced cell size growth and increase in individual mitochondria activity. We also explored several benefits of image-based analysis such as ability to monitor cell number dynamics, dissect changes in total and individual mitochondria activity from cell proliferation, and ability to identify chromatin remodeling drugs. Finally, we provide a web tool that allows comparing results obtained by different methods.

Input data resolution affects the conservation prioritization outcome of spatially sparse biodiversity features.

Detailed spatial data are an essential part of land use planning and decision-making. Their spatial resolution sets limitations to their use, as coarse datasets are not suitable for detecting small-scale phenomena. In this study, we explored the effects of spatial resolution on the ecological outcome of a conservation prioritization process in Zonation software. Our study area was in Evo, southern Finland, covering a mosaic of managed and conserved forests. We produced the feature layers describing the forest characteristics using high-resolution remote sensing datasets, object-based mapping methods, and forest site type data. We found that increasing the resolution above the 16 m baseline resolution resulted in substantial errors. The conservation errors were the highest for rare features related to European Aspen, whereas the common features related to dominant tree species could benefit from the growth of cell size. We conclude that adequate spatial resolution is a prerequisite for efficient conservation prioritization, and that the size and spatial distribution of the features affect the resolution requirements.

Genome Size Covaries More Positively with Propagule Size than Adult Size: New Insights into an Old Problem.

Simple SummaryThe amount of hereditary information (DNA) contained in the cell nuclei of larger or more complex organisms is often no greater than that of smaller or simpler organisms. Why this is so is an evolutionary mystery. Here, I show that the amount of DNA per cell nucleus (‘genome size’) relates more positively to egg size than body size in crustaceans (including shrimp, lobsters and crabs). Genome size also seems to relate more to the size of eggs or other gametes and reproductive propagules (e.g., sperm, spores, pollen and seeds) than to adult size in other animals and plants. I explain these patterns as being the result of genome size relating more to cell size (including that of single-celled eggs) than the number of cells in a body. Since most organisms begin life as single cells or propagules with relatively few cells, propagule size may importantly affect or be affected by genome size regardless of body size. Relationships between genome size and body size should thus become weaker as body size (and the amount of cell multiplication required during development) increases, as observed in crustaceans and other kinds of organisms.The body size and (or) complexity of organisms is not uniformly related to the amount of genetic material (DNA) contained in each of their cell nuclei (‘genome size’). This surprising mismatch between the physical structure of organisms and their underlying genetic information appears to relate to variable accumulation of repetitive DNA sequences, but why this variation has evolved is little understood. Here, I show that genome size correlates more positively with egg size than adult size in crustaceans. I explain this and comparable patterns observed in other kinds of animals and plants as resulting from genome size relating strongly to cell size in most organisms, which should also apply to single-celled eggs and other reproductive propagules with relatively few cells that are pivotal first steps in their lives. However, since body size results from growth in cell size or number or both, it relates to genome size in diverse ways. Relationships between genome size and body size should be especially weak in large organisms whose size relates more to cell multiplication than to cell enlargement, as is generally observed. The ubiquitous single-cell ‘bottleneck’ of life cycles may affect both genome size and composition, and via both informational (genotypic) and non-informational (nucleotypic) effects, many other properties of multicellular organisms (e.g., rates of growth and metabolism) that have both theoretical and practical significance.

Interactive effects of light quality and culturing temperature on algal cell size, biomass doubling time, protein content, and carbohydrate content.

Light management strategy can be used to improve algal biomass and nutrient production. However, the response of algal metabolism to different light qualities, especially their interaction with other environmental factors, is not well understood. This study focuses on the interactive effects of light quality and culturing temperature on algal protein content and carbohydrate content of C. reinhardtii. Three LED light sources (blue light, red-orange light, and white-yellow light) were applied to grow algae in batch cultures with a light intensity of 105 μmol/m2s under the temperatures of 24 °C to 32 °C. The protein and carbohydrate content were measured in both the late exponential growth phase and the late stationary growth phase. The results revealed that there was an interactive effect of light quality and culturing temperature on the protein and carbohydrate content. The combined conditions of blue light and a temperature of 24 °C or 28 °C, which induced a larger algal cell size with a prolonged cell cycle and a low division rate, resulted in the highest protein content; the protein mass fraction and concentration were 32% and 52% higher than that under white-yellow light at 32 °C. The combined conditions of red-orange light and a temperature of 24 °C, which promoted both the cell division and size growth, enhanced the carbohydrate content; the carbohydrate mass fraction and concentration were 161% and 155% higher than that under white-yellow light at 24 °C. When there was temperature stress (32 °C) or nutrient stress, the effect of light quality reduced, and the difference of protein and carbohydrate content among the three light qualities decreased. KEY POINTS: • Studied light quality-temperature interactive effect on protein, carbohydrate synthesis. • Protein content was high under low cell division rate. • Carbohydrate content was high under high cell division and cell size growth rate.

Exponential trajectories, cell size fluctuations, and the adder property in bacteria follow from simple chemical dynamics and division control.

Experiments on steady-state bacterial cultures have uncovered several quantitative regularities at the system level. These include, first, the exponential growth of cell size with time and the balanced growth of intracellular chemicals between cell birth and division, which are puzzling given the nonlinear and decentralized chemical dynamics in the cell. We model a cell as a set of chemical populations undergoing nonlinear mass action kinetics in a container whose volume is a linear function of the chemical populations. This turns out to be a special class of dynamical systems that generically has attractors in which all populations grow exponentially with time at the same rate. This explains exponential balanced growth of bacterial cells without invoking any regulatory mechanisms and suggests that this could be a robust property of protocells as well. Second, we consider the hypothesis that cells commit themselves to division when a certain internal chemical population reaches a threshold of N molecules. We show that this hypothesis leads to a simple explanation of some of the variability observed across cells in a bacterial culture. In particular, it reproduces the adder property of cell size fluctuations observed recently in E. coli; the observed correlations among interdivision time, birth volume, and added volume in a generation; and the observed scale of the fluctuations (CV ≈ 10-30%) when N is between 10 and 100. Third, upon including a suitable regulatory mechanism that optimizes the growth rate of the cell, the model reproduces the observed bacterial growth laws including the dependence of the growth rate and ribosomal protein fraction on the medium. Thus, the models provide a framework for unifying diverse aspects of bacterial growth physiology under one roof. They also suggest new questions for experimental and theoretical enquiry.

Simultaneous induction of distinct protein phase separation events in multiple subcellular compartments of a single cell

Intracellular protein crystallization occurs under various physiological and pathological settings, yet the underlying cellular processes remain enigmatic. After validating individual crystallization events using cellular proteins that readily crystallize in the ER (NEU1), cytosol (crystallin-γD mutant) or nucleus (CLC protein), I demonstrate three independent crystallization events can take place concurrently in different subcellular compartments of a single cell without compromising cell viability. By co-expressing NEU1 and previously reported two human monoclonal antibodies that undergo crystallization and liquid-liquid phase separation in the ER, I additionally demonstrate two independent phase separation events can be simultaneously induced in the ER lumen of a single cell without mixing or interfering each other's phase separation behaviors. Intracellular protein crystallization thus takes place in a crowded physiological cellular environment and does not require high protein purity. Furthermore, I report a simple method to increase the yield of intracellular protein crystals by treating the cells with a topoisomerase II inhibitor that blocks cell division without preventing cell size growth. This study not only presents accessible model tools for studying cryptic in vivo protein crystallization events, but also paves a way toward establishing the intracellular protein crystallization as a novel platform for recombinant protein expression and purification.

Stochastic Individual-Based Modeling of Bacterial Growth and Division Using Flow Cytometry.

A realistic description of the variability in bacterial growth and division is critical to produce reliable predictions of safety risks along the food chain. Individual-based modeling of bacteria provides the theoretical framework to deal with this variability, but it requires information about the individual behavior of bacteria inside populations. In this work, we overcome this problem by estimating the individual behavior of bacteria from population statistics obtained with flow cytometry. For this objective, a stochastic individual-based modeling framework is defined based on standard assumptions during division and exponential growth. The unknown single-cell parameters required for running the individual-based modeling simulations, such as cell size growth rate, are estimated from the flow cytometry data. Instead of using directly the individual-based model, we make use of a modified Fokker-Plank equation. This only equation simulates the population statistics in function of the unknown single-cell parameters. We test the validity of the approach by modeling the growth and division of Pediococcus acidilactici within the exponential phase. Estimations reveal the statistics of cell growth and division using only data from flow cytometry at a given time. From the relationship between the mother and daughter volumes, we also predict that P. acidilactici divide into two successive parallel planes.

Upregulation of eIF6 inhibits cardiac hypertrophy induced by phenylephrine

Cardiac hypertrophy is determined by an increase of cell size in cardiomyocytes (CMCs). Among the cellular processes regulating the growth of cell size, the increase of protein synthesis rate represents a critical event. Most of translational factors promoting protein synthesis stimulate cardiac hypertrophy. In contrast, activity of translational repressor factors, in cardiac hypertrophy, is not fully determined yet. Here we report the effect of a translational modulator, eIF6/p27BBP in the hypertrophy of neonatal rat CMCs. The increase of eIF6 levels surprisingly prevent the growth of cell size induced by phenylephrine, through a block of protein synthesis without affecting skeletal rearrangement and ANF mRNA expression. Thus, this work uncovers a new translational cardiac regulator independent by other well-known factors such as mTOR signalling or eIF2β.

The Ubiquitin Binding Protein TAX1BP1 Mediates Autophagosome Induction and the Metabolic Transition of Activated T Cells

During immune responses, naive Tcells transition from small quiescent cells to rapidly cycling cells. We have found that Tcells lacking TAX1BP1 exhibit delays in growth of cell size and cell cycling. TAX1BP1-deficient Tcells exited G0 but stalled in Sphase, due to both bioenergetic and biosynthetic defects. These defects were due to deficiencies in mTOR complex formation and activation. These mTOR defects in turn resulted from defective autophagy induction. TAX1BP1 binding of LC3 and GABARAP via its LC3-interacting region (LIR), but not its ubiquitin-binding domain, supported Tcell proliferation. Supplementation of TAX1BP1-deficient Tcells with metabolically active L-cysteine rescued mTOR activation and proliferation but not autophagy. These studies reveal that TAX1BP1 drives a specialized form of autophagy, providing critical amino acids that activate mTOR and enable the metabolic transition of activated Tcells.

Growth of the Mammalian Golgi Apparatus during Interphase.

During the cell cycle, genetic materials and organelles are duplicated to ensure that there is sufficient cellular content for daughter cells. While Golgi growth in interphase has been observed in lower eukaryotes, the elaborate ribbon structure of the mammalian Golgi apparatus has made it challenging to monitor. Here we demonstrate the growth of the mammalian Golgi apparatus in its protein content and volume during interphase. Through ultrastructural analyses, physical growth of the Golgi apparatus was revealed to occur by cisternal elongation of the individual Golgi stacks. By examining the timing and regulation of Golgi growth, we established that Golgi growth starts after passage through the cell growth checkpoint at late G1 phase and continues in a manner highly correlated with cell size growth. Finally, by identifying S6 kinase 1 as a major player in Golgi growth, we revealed the coordination between cell size and Golgi growth via activation of the protein synthesis machinery in early interphase.

VprBP, an HIV target protein, is vital for immune responses by controlling T cell growth, proliferation and senescence.

Abstract Naïve mature T cells are maintained in a quiescent state with a low rate of cell size growth (biomass increase due to enhanced metabolism and biosynthesis) and proliferation. Disturbances inflicted by infection and inflammation, often trigger cells to exit quiescence and enter cell cycle, followed by rapid proliferation to restore homeostasis. Cell size growth is imperative for proliferating cells to compensate for the halving of cellular constituents for each division. Thus, proper coordination of cell growth and cell cycle entry of T cells is essential to mount effective immune response. Nonetheless, little is known about how cell cycle entry is controlled and even less about how cell size growth is regulated in T cells. We studied protein expression during T cell growth and cell cycle entry using quantitative proteomic approach. VprBP, an HIV target protein, was identified to be one of the highly upregulated factors. We found that VprBP was required for the cell growth and cell cycle entry of activated T cells. VprBP deletion abrogated T cell expansion during antiviral and autoimmune responses in vivo. VprBP-deficient cells drastically stabilized p53 protein with elevated expression of p53 target genes. Intriguingly, we found that although p53 deletion failed to correct the T cell growth defect due to VprBP deletion, it largely restored the cell cycle entry of VprBP-deficient T cells. In addition, VprBP deletion led to a premature senescence phenotype in T cells associating with increased cellular aging markers. These results suggest that VprBP controls T cell growth, cell cycle entry and senescence via discrete molecular programs. The recent findings and the underlying mechanisms will be discussed in detail in this presentation.

Shape dynamics of growing cell walls.

We introduce a general theoretical framework to study the shape dynamics of actively growing and remodeling surfaces. Using this framework we develop a physical model for growing bacterial cell walls and study the interplay of cell shape with the dynamics of growth and constriction. The model allows us to derive constraints on cell wall mechanical energy based on the observed dynamics of cell shape. We predict that exponential growth in cell size requires a constant amount of cell wall energy to be dissipated per unit volume. We use the model to understand and contrast growth in bacteria with different shapes such as spherical, ellipsoidal, cylindrical and toroidal morphologies. Coupling growth to cell wall constriction, we predict a discontinuous shape transformation, from partial constriction to cell division, as a function of the chemical potential driving cell wall synthesis. Our model for cell wall energy and shape dynamics relates growth kinetics with cell geometry, and provides a unified framework to describe the interplay between shape, growth and division in bacterial cells.

Synergistic Effects of Modification with Nanoclay and Polystyrene on the Foaming Behavior of a Random Copolymerized Polypropylene

Microcellular polypropylene/polystyrene/nanoclay (PP/PS/nanoclay) composites were processed in a continuous extrusion foaming system using supercritical CO2 as the foaming agent. Neat PP foam showed quite a broad distribution of cell sizes and thick cell walls. Under the same foaming conditions, nanoclay and PS were introduced in the foaming process of PP. Consequently, foams with uniform cell size distribution, reduced cell size of 10~30 μm and enhanced cell-population density of 2.16×108 cells/cm3 were obtained. The heterogeneous nucleation of PS and nanoclay dramatically increased the nucleation rate, decreased the nucleation time interval, and hence facilitated an almost instantaneous growth of cell size. This method also provided new insight into the mechanism of improving the foaming performance of PP.

Be quiet and you'll keep young: does mTOR underlie p53 action in protecting against senescence by favoring quiescence?

Be quiet and you'll keep young: does mTOR underlie p53 action in protecting against senescence by favoring quiescence?

Hypertrophy and/or Hyperplasia: Dynamics of Adipose Tissue Growth

Adipose tissue grows by two mechanisms: hyperplasia (cell number increase) and hypertrophy (cell size increase). Genetics and diet affect the relative contributions of these two mechanisms to the growth of adipose tissue in obesity. In this study, the size distributions of epididymal adipose cells from two mouse strains, obesity-resistant FVB/N and obesity-prone C57BL/6, were measured after 2, 4, and 12 weeks under regular and high-fat feeding conditions. The total cell number in the epididymal fat pad was estimated from the fat pad mass and the normalized cell-size distribution. The cell number and volume-weighted mean cell size increase as a function of fat pad mass. To address adipose tissue growth precisely, we developed a mathematical model describing the evolution of the adipose cell-size distributions as a function of the increasing fat pad mass, instead of the increasing chronological time. Our model describes the recruitment of new adipose cells and their subsequent development in different strains, and with different diet regimens, with common mechanisms, but with diet- and genetics-dependent model parameters. Compared to the FVB/N strain, the C57BL/6 strain has greater recruitment of small adipose cells. Hyperplasia is enhanced by high-fat diet in a strain-dependent way, suggesting a synergistic interaction between genetics and diet. Moreover, high-fat feeding increases the rate of adipose cell size growth, independent of strain, reflecting the increase in calories requiring storage. Additionally, high-fat diet leads to a dramatic spreading of the size distribution of adipose cells in both strains; this implies an increase in size fluctuations of adipose cells through lipid turnover.

Bioassays with Unicellular Algae: Deviations from Exponential Growth and Its Implications for Toxicity Test Results

Growth assays with unicellular green algae are an established tool in ecotoxicological effect assessment for chemicals and environmental samples. From an ecological perspective it seems appropriate to use the growth rate as a process variable rather than a measure of biomass gain for calculating inhibitory effects of contaminants. The notion of simple exponential growth for the description of the population increase in undisturbed suspension cultures of unicellular green algae, however, seems to be an oversimplification. Experimental findings describe the increase in biomass, cell number, the development of cell volume distributions of populations, and the relationship between cell size and chlorophyll content for individual cells over one generation at a time resolution of 2-h intervals. It was observed that algal populations of Desmodesmus subspicatus show a time pattern of cell size growth; the average cell volume increases about sixfold, without corresponding increase in population size. This is followed by a distinct cell division phase with little gain in biomass. This synchronous growth behavior despite continuous illumination may be explained by the multiple fission characteristic of unicellular green algae which is an adaptation to cyclic light-dark changes in the environment. It might be controlled by an independent cell cycle clock. For routine regulatory testing fluorescence-based measurements rather than cell counting minimizes the confounding effect on toxicity determination. For investigations of time-dependent effects, e.g., by pulsed exposure, an alternative mechanistically based growth function for unicellular algae is proposed that accommodates for the observed growth pattern.

Heterogeneous nucleation uniformizing cell size distribution in microcellular nanocomposites foams

Microcellular polycarbonate/nano-silica nanocomposites (PCSN) were prepared by temperature rising process using supercritical CO 2 as the blowing agent. Neat PC foam showed a quite broad distribution of cell sizes. Under the same foaming conditions, the addition of nano-silica resulted in PCSN foams having uniform cell size distribution, reduced cell size of 0.3–0.5 μm and increased cell density of 10 11–10 13 cells/cm 3. The underlying nucleation mechanism was semi-quantitatively analyzed by the classical nucleation theory. The results indicate that the energy-barrier for heterogeneous nucleation was three orders of magnitude lower than that of homogeneous one. The heterogeneous nucleation of nano-silica aggregates dramatically increased the nucleation rate, decreased the nucleation time interval, and hence facilitated the almost instantaneous growth of cell size. Combined with the well-dispersed nucleation sites, resulted from the uniform dispersion of nano-silica aggregates, the narrow-distributed cell size was obtained in PCSN foams.

Rational role of amino acids in intestinal epithelial cells (Review)

There is much interest in precise functions of amino acids on mammalian growth and development. Some of amino acids play important roles in the control of gene expression by controlling the initiation phase of mRNA translation. The signal induced by leucine or arginine may stimulate cell growth. On the other hand, the other signal induced by glutamine may stimulate cellular proliferation and increase cell number, but inhibit the growth of cell size. However, there was no clear evidence that an individual amino acid specifically works as a signaling molecule. In our recent study, not only leucine, but also arginine is shown to activate the mTOR signaling pathway in rat intestinal epithelial cells. Furthermore, regarding L-Glutamine, an important amino acid that is required for culturing of numerous cell types, including rat intestinal epithelial cells, we have shown that it had an inhibitory effect on leucine- or arginine-induced activation of the mTOR signaling pathway. We have demonstrated that L-Glutamine inhibited the activation of p70 S6 kinase and phosphorylation of 4E-BP1 induced by arginine or leucine in rat intestinal epithelial cells. Based on these results, we are planning to confirm the effect of each amino acid including glutamine in an in vivo model using new born mice.

Substrate Enhances the Sensitivity of Type I Protein Kinase A to cAMP

The functional significance of the presence of two major (types I and II) isoforms of the cAMP-dependent protein kinase (PKA) is still enigmatic. The present study showed that peptide substrate enhanced the activation of PKA type I at low, physiologically relevant concentrations of cAMP through competitive displacement of the regulatory RI subunit. The effect was similar whether the substrate was a short peptide or the physiological 60-kDa protein tyrosine hydroxylase. In contrast, substrate failed to affect the cAMP-sensitivity of PKA type II. Size exclusion chromatography confirmed that substrate acted to physically enhance the dissociation of the RIalpha and Calpha subunits of PKA type I, but not the RIIalpha and Calpha subunits of PKA type II. Substrate availability can therefore fine-tune the activation of PKA type I by cAMP, but not PKA type II. The cAMP-dissociated RII and C subunits of PKA type II reassociated much faster than the PKA type I subunits in the presence of substrate peptide. This suggests that only PKA type II is able to rapidly reverse its activation after a burst of cAMP when exposed to high substrate concentration. We propose this as a possible reason why PKA type II is preferentially found in complexes with substrates undergoing rapid phosphorylation cycles.