Rate Of Cell Division Research Articles

Module to Support Real-Time Microscopic Imaging of Living Organisms on Ground-Based Microgravity Analogs

Since opportunities for spaceflight experiments are scarce, ground-based microgravity simulation devices (MSDs) offer accessible and economical alternatives for gravitational biology studies. Among the MSDs, the random positioning machine (RPM) provides simulated microgravity conditions on the ground by randomizing rotating biological samples in two axes to distribute the Earth’s gravity vector in all directions over time. Real-time microscopy and image acquisition during microgravity simulation are of particular interest to enable the study of how basic cell functions, such as division, migration, and proliferation, progress under altered gravity conditions. However, these capabilities have been difficult to implement due to the constantly moving frames of the RPM as well as mechanical noise. Therefore, we developed an image acquisition module that can be mounted on an RPM to capture live images over time while the specimen is in the simulated microgravity (SMG) environment. This module integrates a digital microscope with a magnification range of 20× to 700×, a high-speed data transmission adaptor for the wireless streaming of time-lapse images, and a backlight illuminator to view the sample under brightfield and darkfield modes. With this module, we successfully demonstrated the real-time imaging of human cells cultured on an RPM in brightfield, lasting up to 80 h, and also visualized them in green fluorescent channel. This module was successful in monitoring cell morphology and in quantifying the rate of cell division, cell migration, and wound healing in SMG. It can be easily modified to study the response of other biological specimens to SMG.

ECM Remodeling and an Abrupt, Stochastic Transition to Arrest Determine Tissue Growth Kinetics

During development, multicellular organisms undergo stereotypical patterns of tissue growth in space and time, but how this is orchestrated remains unclear. Drosophila histoblast nests are small clusters of progenitor epithelial cells that undergo extensive growth to give rise to the abdominal epidermis and are amenable to live-imaging. Our quantitative analysis of the temporal dynamics of abdomen growth reveals that histoblasts display oscillatory cell division rates and that growth termination occurs through the rapid emergence of arrested cells rather than a gradual increase in cell cycle time. By examining tissue mechanics throughout histoblast expansion, we uncover an increase in tissue stress together with a decrease in extracellular matrix resistance as the histoblasts expand. The decrease in resistance is driven by timely extracellular matrix remodeling, which is necessary to trigger tissue expansion. Thus, changes in the tissue microenvironment, and a rapid cell cycle exit, control the formation of the adult Drosophila abdomen.

Environmental and developmental factors driving xylem anatomy and micro-density in black spruce.

Wood density is the product of carbon allocation for structural growth and reflects the trade-off between mechanical support and water conductivity. We tested a conceptual framework based on the assumption that micro-density depends on direct and indirect relationships with endogenous and exogenous factors. The dynamics of wood formation, including timings and rates of cell division, cell enlargement, and secondary wall deposition, were assessed from microcores collected weekly between 2002 and 2016 from five black spruce stands located along a latitudinal gradient in Quebec, Canada. Cell anatomy and micro-density were recorded by anatomical analyses and X-ray measurements. Our structural equation model explained 80% of micro-density variation within the tree-ring with direct effects of wall thickness (σ=0.61), cell diameter (σ=-0.51), and photoperiod (σ=-0.26). Wood formation dynamics had an indirect effect on micro-density. Micro-density increased under longer periods of cell-wall deposition and shorter durations of enlargement. Our results fill a critical gap in understanding the relationships underlying micro-density variation in conifers. We demonstrated that short-term responses to environmental variations could be overridden by plastic responses that modulate cell differentiation. Our results point to wood formation dynamics as a reliable predictor of carbon allocation in trees.

Mechanochemical control of epidermal stem cell divisions by B-plexins

The precise spatiotemporal control of cell proliferation is key to the morphogenesis of epithelial tissues. Epithelial cell divisions lead to tissue crowding and local changes in force distribution, which in turn suppress the rate of cell divisions. However, the molecular mechanisms underlying this mechanical feedback are largely unclear. Here, we identify a critical requirement of B-plexin transmembrane receptors in the response to crowding-induced mechanical forces during embryonic skin development. Epidermal stem cells lacking B-plexins fail to sense mechanical compression, resulting in disinhibition of the transcriptional coactivator YAP, hyperproliferation, and tissue overgrowth. Mechanistically, we show that B-plexins mediate mechanoresponses to crowding through stabilization of adhesive cell junctions and lowering of cortical stiffness. Finally, we provide evidence that the B-plexin-dependent mechanochemical feedback is also pathophysiologically relevant to limit tumor growth in basal cell carcinoma, the most common type of skin cancer. Our data define a central role of B-plexins in mechanosensation to couple cell density and cell division in development and disease.

Increased stem cell proliferation in atherosclerosis accelerates clonal hematopoiesis

Clonal hematopoiesis, a condition in which individual hematopoietic stem cell clones generate a disproportionate fraction of blood leukocytes, correlates with higher risk for cardiovascular disease. The mechanisms behind this association are incompletely understood. Here, we show that hematopoietic stem cell division rates are increased in mice and humans with atherosclerosis. Mathematical analysis demonstrates that increased stem cell proliferation expedites somatic evolution and expansion of clones with driver mutations. The experimentally determined division rate elevation in atherosclerosis patients is sufficient to produce a 3.5-fold increased risk of clonal hematopoiesis by age 70. We confirm the accuracy of our theoretical framework in mouse models of atherosclerosis and sleep fragmentation by showing that expansion of competitively transplanted Tet2-/- cells is accelerated under conditions of chronically elevated hematopoietic activity. Hence, increased hematopoietic stem cell proliferation is an important factor contributing to the association between cardiovascular disease and clonal hematopoiesis.

Characterization of the development dynamics within the linear growth bamboo leaf.

The leaf is the main photosynthetic organ in plants, such as bamboo. Leaves from bamboo are used as a food additive. However, according to our investigation, to date there have been no reports concerning the leaf development of bamboo. By measuring over 7500 parenchymal cells, we discovered that the linear leaf growth of Pseudosasa japonica could be divided into three growth sections. The first one is a roughly 1-cm long division zone (DZ), containing about 1580 cells, located at the bottom of the leaf; the second one is an about 3-cm long elongation zone (EZ), with ~1905 cells, located above the DZ; and the last is a mature zone (MZ) in which cell elongation is completed. The cell production rate of the DZ was 25.33-35.81 cells per hour, with an average of 29.73; and the cell division rate was ~0.45 cells per cell every 24 h. PacBio and Illumina transcriptome sequencing found 21 933 unigenes expressed in these zones. Further analysis revealed a dynamic transcriptome, with transcripts for cell division in the DZ changing to transcripts for cell elongation, photosynthetic development, secondary metabolism, stress resistance, and nutrition transport toward the leaf distal. Those transcriptome transformations correlated well with the changes of relative water content, biomass accumulation, and cellulose crystal degree and were supported by quantitative polymerase chain reaction data. These results revealed a developmental gradient of the bamboo linear growth leaf, which offers a foundation to elucidate and engineer leaf development in bamboo, an economically valuable plant.

Cytogenotoxicity of the water and sediment of the Paraopeba River immediately after the iron ore mining dam disaster (Brumadinho, Minas Gerais, Brazil)

The present study evaluated the toxicogenetic potential of the water and sediment from Paraopeba River, five days after the rupture of the mining tailings dam at Brumadinho (Minas Gerais, Brazil), on January 2019, by Allium cepa test. Water samples collected at sites closest to the collapsed dam caused a higher frequency of genetic damage and lower cell division rate compared to the upstream site. In sediment it was observed a decrease in the cell division rate and genetic damage in the sampling sites closest to the dam. The frequency of aberrations and the mitotic index in A. cepa cells exposed to sediments were negatively associated with the levels of most elements in total and bioavailable fractions. A negative association between some metal concentrations in total and dissolved water with the mitotic index was also observed. Otherwise, the genotoxic effects were positively correlated with the concentrations of most metals. The results demonstrate the potential of the tailings to cause cytogenotoxic effects due the higher metal concentrations released in water column and in sediments. This is the first report highlighting the toxicogenetic potential of the released tailings and reinforce the need for a long-term monitoring of the watershed due the advance of the tailings plume through Paraopeba River over time.

Влияние хронического ионизирующего излучения на вариабельность митотической активности тканей Pinus sylvestris L.

The development of nuclear power engineering will increase in the future, due to the continued likelihood of radionuclides entering the environment. The relevance of studying the genetic material of conifers as a reliable bioindicator was revealed. It is known that under the influence of ionizing radiation there is an accumulation of genetic abnormalities in pine (Pinus sylvestris L.) progeny. The stages of gametogenesis, zygotes and young seedlings of plant organisms are most sensitive to ionizing radiation. It is important to determine the variability of the mitotic index (MI) of tissues of Scots pine (Pinus sylvestris L.) progeny in areas with different levels of ionizing radiation, including in the exclusion zone. The exposure dose rate was measured at the soil level and 1 m from the ground surface. Germination of seeds was carried out in a thermostat on wet filter paper. Roots of seedlings 0.5–1 cm long were fixed in a mixture of 96 % ethanol and glacial acetic acid. Root staining was carried out in a solution of acetocarmine. Tissue softening was carried out with a strong chloral hydrate solution. The total number of dividing cells, as well as pathological mitoses (PM) were counted on squash preparations using a microscope. The mitotic index and the duration of the phases of mitosis were determined. An increase in the level of radioactive contamination increases the cell division rate in prophase, anaphase, and telophase, but decreases the duration of metaphase, and also changes the relative duration of mitosis phases. With an increase in the exposure dose rate, the number of pathological mitoses naturally increases. The spectrum of mitosis disorders is represented by various abnormalities of the chromosome apparatus in anaphase: exit and lagging of chromosomes, bridges. Herewith, the number of anaphases with bridges increases significantly with simultaneous exit and lagging of chromosomes.

The Photosynthetic Bacterium Rhodopseudomonas palustris Strain PS3 Exerts Plant Growth-Promoting Effects by Stimulating Nitrogen Uptake and Elevating Auxin Levels in Expanding Leaves.

Rhodopseudomonas palustris strain PS3, a phototrophic bacterium, was originally isolated from a paddy field located in Taipei city, Taiwan, and showed positive effects on the growth of leafy vegetables. The aim of this study was to clarify the mechanism of the beneficial effects exerted by PS3 on plants. An ineffective R. palustris strain, YSC3, isolated from a paddy field located in Yilan County, was used as the negative control for comparative analyses. We cultivated non-heading Chinese cabbage (Brassica rapa var. chinensis) in 1/2 strength Hoagland hydroponic solution, in which nitrate is the main nitrogen source. We evaluated various plant physiological responses to inoculation with different bacterial inoculants. The N use efficiency (NUE) of PS3-inoculated plants was dramatically higher than that of YSC3-inoculated plants. The nitrate uptake efficiency (NUpE) was significantly elevated in plants treated with PS3; however, no excess nitrate accumulation was observed in leaves. We also noticed that the endogenous indole-3-acetic acid (IAA) levels as well as the cell division rate in the leaves of PS3-inoculated plants were significantly higher than those in the leaves of YSC3-inoculated plants. We examined the bacterial transcription of some genes during root colonization, and found that the expression level of IAA synthesis related gene MAO was almost the same between these two strains. It suggests that the elevated endogenous IAA in the PS3-inoculated plants was not directly derived from the exogenous IAA produced by this bacterium. Taken together, we deduced that PS3 inoculation could promote plant growth by enhancing nitrate uptake and stimulating the accumulation of endogenous auxin in young expanding leaves to increase the proliferation of leaf cells during leaf development.

Insights on the Control of Yeast Single-Cell Growth Variability by Members of the Trehalose Phosphate Synthase (TPS) Complex.

Single-cell variability of growth is a biological phenomenon that has attracted growing interest in recent years. Important progress has been made in the knowledge of the origin of cell-to-cell heterogeneity of growth, especially in microbial cells. To better understand the origins of such heterogeneity at the single-cell level, we developed a new methodological pipeline that coupled cytometry-based cell sorting with automatized microscopy and image analysis to score the growth rate of thousands of single cells. This allowed investigating the influence of the initial amount of proteins of interest on the subsequent growth of the microcolony. As a preliminary step to validate this experimental setup, we referred to previous findings in yeast where the expression level of Tsl1, a member of the Trehalose Phosphate Synthase (TPS) complex, negatively correlated with cell division rate. We unfortunately could not find any influence of the initial TSL1 expression level on the growth rate of the microcolonies. We also analyzed the effect of the natural variations of trehalose-6-phosphate synthase (TPS1) expression on cell-to-cell growth heterogeneity, but we did not find any correlation. However, due to the already known altered growth of the tps1Δ mutants, we tested this strain at the single-cell level on a permissive carbon source. This mutant showed an outstanding lack of reproducibility of growth rate distributions as compared to the wild-type strain, with variable proportions of non-growing cells between cultivations and more heterogeneous microcolonies in terms of individual growth rates. Interestingly, this variable behavior at the single-cell level was reminiscent to the high variability that is also stochastically suffered at the population level when cultivating this tps1Δ strain, even when using controlled bioreactors.

Jasmonates, Ethylene and Brassinosteroids Control Adventitious and Lateral Rooting as Stress Avoidance Responses to Heavy Metals and Metalloids.

Developmental and environmental signaling networks often converge during plant growth in response to changing conditions. Stress-induced hormones, such as jasmonates (JAs), can influence growth by crosstalk with other signals like brassinosteroids (BRs) and ethylene (ET). Nevertheless, it is unclear how avoidance of an abiotic stress triggers local changes in development as a response. It is known that stress hormones like JAs/ET and BRs can regulate the division rate of cells from the first asymmetric cell divisions (ACDs) in meristems, suggesting that stem cell activation may take part in developmental changes as a stress-avoidance-induced response. The root system is a prime responder to stress conditions in soil. Together with the primary root and lateral roots (LRs), adventitious roots (ARs) are necessary for survival in numerous plant species. AR and LR formation is affected by soil pollution, causing substantial root architecture changes by either depressing or enhancing rooting as a stress avoidance/survival response. Here, a detailed overview of the crosstalk between JAs, ET, BRs, and the stress mediator nitric oxide (NO) in auxin-induced AR and LR formation, with/without cadmium and arsenic, is presented. Interactions essential in achieving a balance between growth and adaptation to Cd and As soil pollution to ensure survival are reviewed here in the model species Arabidopsis and rice.

ASYMMETRICAL CELL DIVISION WITH EXPONENTIAL GROWTH

AbstractAn advanced pantograph-type partial differential equation, supplemented with initial and boundary conditions, arises in a model of asymmetric cell division. Methods for solving such problems are limited owing to functional (nonlocal) terms. The separation of variables entails an eigenvalue problem that involves a nonlocal ordinary differential equation. We discuss plausible eigenvalues that may yield nontrivial solutions to the problem for certain choices of growth and division rates of cells. We also consider the asymmetric division of cells with linear growth rate which corresponds to “exponential growth” and exponential rate of cell division, and show that the solution to the problem is a certain Dirichlet series. The distribution of the first moment of the biomass is shown to be unimodal.

Optimal experimental design for mathematical models of haematopoiesis.

The haematopoietic system has a highly regulated and complex structure in which cells are organized to successfully create and maintain new blood cells. It is known that feedback regulation is crucial to tightly control this system, but the specific mechanisms by which control is exerted are not completely understood. In this work, we aim to uncover the underlying mechanisms in haematopoiesis by conducting perturbation experiments, where animal subjects are exposed to an external agent in order to observe the system response and evolution. We have developed a novel Bayesian hierarchical framework for optimal design of perturbation experiments and proper analysis of the data collected. We use a deterministic model that accounts for feedback and feedforward regulation on cell division rates and self-renewal probabilities. A significant obstacle is that the experimental data are not longitudinal, rather each data point corresponds to a different animal. We overcome this difficulty by modelling the unobserved cellular levels as latent variables. We then use principles of Bayesian experimental design to optimally distribute time points at which the haematopoietic cells are quantified. We evaluate our approach using synthetic and real experimental data and show that an optimal design can lead to better estimates of model parameters.

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.

The Rates of Stem Cell Division Determine the Cell Cycle Lengths of Its Lineage

Adult stem cells and their transit-amplifying progeny alter their proliferation rates to maintain tissue homeostasis. To test how the division rates of stem cells and transit-amplifying progeny affect tissue growth and differentiation, we developed a computation strategy that estimates the average cell-cycle lengths (lifespans) of germline stem cells and their progeny from fixed-tissue demography in the Drosophila testis. Analysis of the wild-type data using this method indicated that during the germline transit-amplification, the cellular lifespans extend by nearly 1.3-fold after the first division and shrink by about 2-folds after the second division. Cell-autonomous perturbations of the stem cell lifespan accordingly altered the lifespans of successive transit-amplifying stages. Remarkably, almost 2-fold alterations in the lifespans of stem cells and their immediate daughters did not affect the subsequent differentiation. Together, the results indicate that the early germline division rates can adjust the following division rates and the onset of differentiation.

Cell size: a key determinant of meristematic potential in plant protoplasts.

Metabolic pathway reconstruction and gene edits for native natural product synthesis in single plant cells are considered to be less complicated when compared to the production of non-native metabolites. Being an efficient eukaryotic system, plants encompass suitable post-translational modifications. However, slow cell division rate and heterogeneous nature is an impediment for consistent product retrieval from plant cells. Plant cell synchrony can be attained in cultures developed in vitro. Isolated plant protoplasts capable of division, can potentially enhance the unimpaired yield of target bioactives, similar to microbes and unicellular eukaryotes. Evidence from yeast experiments suggests that 'critical cell size' and division rates for enhancement machinery, primarily depend on culture conditions and nutrient availability. The cell size control mechanisms in Arabidopsis shoot apical meristem is analogous to yeast notably, fission yeast. If protoplasts isolated from plants are subjected to cell size studies and cell cycle progression in culture, it will answer the underlying molecular mechanisms such as, unicellular to multicellular transition states, longevity, senescence, 'cell-size resetting' during organogenesis, and adaptation to external cues.

Plant stem-cell organization and differentiation at single-cell resolution

Plants maintain populations of pluripotent stem cells in shoot apical meristems (SAMs), which continuously produce new aboveground organs. We used single-cell RNA sequencing (scRNA-seq) to achieve an unbiased characterization of the transcriptional landscape of the maize shoot stem-cell niche and its differentiating cellular descendants. Stem cells housed in the SAM tip are engaged in genome integrity maintenance and exhibit a low rate of cell division, consistent with their contributions to germline and somatic cell fates. Surprisingly, we find no evidence for a canonical stem-cell organizing center subtending these cells. In addition, trajectory inference was used to trace the gene expression changes that accompany cell differentiation, revealing that ectopic expression of KNOTTED1 (KN1) accelerates cell differentiation and promotes development of the sheathing maize leaf base. These single-cell transcriptomic analyses of the shoot apex yield insight into the processes of stem-cell function and cell-fate acquisition in the maize seedling and provide a valuable scaffold on which to better dissect the genetic control of plant shoot morphogenesis at the cellular level.

Photoacclimation to high-light stress in Chlamydomonas reinhardtii during conditional senescence relies on generating pH-dependent, high-quenching centres

Microalgae can respond to long-term increases in light intensity by altering the concentration of photosynthetic complexes. Under active growth, the ability of Chlamydomonas reinhardtii to acclimate to excess light is dependent on cell division to reduce the concentration of photosynthetic complexes. But, in batch culture, cells eventually reach stationary phase where their ability to divide is limited; this should impact their capacity to undergo photoacclimation. Our goal is to dissect excess-light responses as cells approach stationary phase and to determine how the strategies of photoacclimation differ compared to cells in the exponential-growth phase. In this study, cultures exited exponential growth and transitioned into a declining growth phase (DGP), where cells continued a slow rate of growth for the next seven days in both low (LL) and high-light (HL). During this period, both cultures experience a conditional senescence-related decline in chlorophyll levels. Under HL, however, the senescing cultures have a rapid decline in PSII reaction centres, maintain a stable concentration of LHCII antenna, rapidly increase LHCSR levels, and have a sustained increase in Fo/Fm. Collectively this implies that the remaining antenna act as pH-dependent, quenching centres, presumably to protect the senescing chloroplast against HL. We discovered that acclimating to HL post-exponential phase involves active degradation that is intertwined with the normal senescence process that allowed for a limited rate of cell division.

Mutation bias within oncogene families is related to proliferation-specific codon usage

It is well known that in cancer gene families some members are more frequently mutated in tumor samples than their family counterparts. A paradigmatic case of this phenomenon is KRAS from the RAS family. Different explanations have been proposed ranging from differential interaction with other proteins to preferential expression or localization. Interestingly, it has been described that despite the high amino acid identity between RAS family members, KRAS employs an intriguing differential codon usage. Here, we found that this phenomenon is not exclusive to the RAS family. Indeed, in the RAS family and other oncogene families with two or three members, the most prevalently mutated gene in tumor samples employs a differential codon usage that is characteristic of genes involved in proliferation. Prompted by these observations, we chose the RAS family to experimentally demonstrate that the translation efficiency of oncogenes that are preferentially mutated in tumor samples is increased in proliferative cells compared to quiescent cells. These results were further validated by assessing the translation efficiency of KRAS in cell lines that differ in their tRNA expression profile. These differences are related to the cell division rate of the studied cells and thus suggest an important role in context-specific oncogene expression regulation. Altogether, our study demonstrates that dynamic translation programs contribute to shaping the expression profiles of oncogenes. Therefore, we propose this codon bias as a regulatory layer to control cell context-specific expression and explain the differential prevalence of mutations in certain members of oncogene families.

Cell cycle events and expression of cell cycle regulators are determining factors in differential grain filling in rice spikelets based on their spatial location on compact panicles.

Rice being a staple crop for human, its production is required to be increased significantly, particularly keeping in view the expected world's population of 9.6 billion by the year 2050. In this context, although the rice breeding programs have been successful in increasing the number of spikelets per panicle, the basal spikelets remain poorly filled, undermining the yield potential. The present study also found the grain filling to bear negative correlation with the panicle grain density. The poorly filled basal spikelets of the compact-panicle cultivars showed a lower endosperm cell division rate and ploidy status of the endosperm nuclei coupled with no significant greater expression of CYCB;1 and CYCH;1 compared with the apical spikelets, unlike that observed in the lax-panicle cultivars, which might have prevented them from overcoming apical dominance. Significantly greater expression of CYCB2;2 in the basal spikelets than in the apical spikelets might also have prevented the former to enter into endoreduplication. Furthermore, expression studies of KRPs in the caryopses revealed that a higher expression of KRP;1 and KRP;4 in the basal spikelets than in the apical spikelets of the compact-panicle cultivars could also be detrimental to grain filling in the former, as KRPs form complex primarily with CDKA-CYCD that promotes S-phase activity and G1/S transition, and thus inhibits endosperm cell division. The study indicates that targeted manipulation of expression of CYCB1;1, CYCB2;2, CYCH1;1, KRP;1 and KRP4 in the basal spikelets of the compact-panicle cultivars may significantly improve their yield performance.