Mechanism Of Division Research Articles

Comparative analysis of anatomy, gene expression of Vaccinium corymbosum cyclins and cyclin dependent kinases during the flower bud and fruit ontogeny

Cell-cycle system controls flower and fruit growth, size and mass precisely, accompanied by cumulative cell proliferation and cell expansion. Vaccinium corymbosum shows significant variation in berry size, but its underlying anatomical and molecular mechanisms are poorly known. In this study, single fruit mass and cell layers of Southern highbush blueberry cultivars 'O'Neal' and 'Bluerain' were analyzed, and 12 cell-cycle related genes were isolated and detected its expression tendency. The results showed that blueberry flower buds had a lower contribution to mature fruit mass, and fruit growth exhibited a double-sigmoid pattern. Ovary wall (or pericarp) was the vital component for final fruit size, and approximately 70% cell layers of pericarp were produced before anthesis. Cell division in the blueberry fruit was arrested at pre- and post-anthesis. The sequences of Vccyclins and VcCDKs were relatively conserved, and its expression tendency followed flower bud and fruit developmental pattern, while VcCycA2L, VcCycB2L, VcCycD3;1L, VcCycT1;4L, VcCDKB2;2, VcCDKC1L and VcCDKE1 might be directly involved in cell proliferation and cell expansion. However, the difference of expression pattern between two cultivars was not quite significant, indicated that isolated Vccyclins and VcCDKs were not the key factors for blueberry fruit size. Collectively, this study expands our understanding of the complex cell division and cell expansion mechanisms, and cell-cycle regulatory mechanisms were involved in V. corymbosum flower and fruit during ontogeny.

A stimulus–response-based allocation method for the circle packing problem with equilibrium constraints

Based on the industrial background of packing objects inside the satellites, this paper addresses the circle packing problem with equilibrium constraints. From a new view of any solid material occupying certain space, a solution of the problem can be seen as different circular objects occupy different space in the container. Hence, the circle packing problem can be treated as a space allocation problem of allocating the container space reasonably to circular objects. Through the mapping between the task allocation in swarm intelligence labor division and the space allocation in circle packing problems, we propose a stimulus–response-based allocation (SRA) method. In this paper, we design four actions, viz., fix, shift, jump and swap, for circular objects to occupy the container space. The SRA method adopts the stimulus–response mechanism of labor division to regulate the actions performed on circular objects. With the characteristic of flexibility inherent in the stimulus–response mechanism, SRA could achieve an effective space allocation under dynamically changed packing environments. Three sets of 35 benchmark instances are used to test the performance of SRA, and SRA improves the best-known results on 28 instances, matches 4 and misses 3.

Mitochondrial Behavior

Mitochondria are double membrane-bounded organelles that perform a myriad of diverse and essential functions in cells. These functions are dependent on the collective intracellular behavior of the organelle. We have characterized key features of mitochondrial behaviors. Our work has addressed the physiological functions and mechanisms of mitochondrial division and fusion, which are important determinants of overall mitochondrial shape and distribution. We have characterized contact sites that intimately link mitochondria with the ER and determined their roles in mitochondrial positioning and dynamics. We have also addressed the fundamental question of how mitochondrial membranes are sub-compartmentalized to reveal how the complex internal architecture of the organelle is generated. Our current challenge is to determine how mitochondrial behaviors are integrated with one another and physiologically regulated within cells and organisms.

Gene expression is more strongly associated with behavioural specialization than with age or fertility in ant workers.

The ecological success of social insects is based on division of labour, not only between queens and workers, but also among workers. Whether a worker tends the brood or forages is influenced by age, fertility and nutritional status, with brood carers being younger, more fecund and more corpulent. Here, we experimentally disentangle behavioural specialization from age and fertility inTemnothorax longispinosus ant workers and analyse how these parameters are linked to whole-body gene expression. A total of 3,644 genes were associated with behavioural specialization which is ten times more than associated with age and 50 times more than associated with fertility. Brood carers were characterized by an upregulation of three Vitellogenin (Vg) genes, one of which, Vg-like A, was the most differentially expressed gene that was recently shown experimentally to control the switch from brood to worker care. The expression of Conventional Vg was unlinked to behavioural specialization, age or fertility, which contrasts to studies on bees and some ants. Diversity in Vg/Vg-like copy number and expression bias across ants supports subfunctionalization of Vg genes and indicates that some regulatory mechanisms of division of labour diverged in different ant lineages. Simulations revealed that our experimental dissociation of co-varying factors reduced transcriptomic noise, suggesting that confounding factors could potentially explain inconsistencies across transcriptomic studies of behavioural specialization in ants. Thus, our study reveals that worker gene expression is mainly linked to the worker's function for the colony and provides novel insights into the evolution of sociality in ants.

Pore Network Investigation of Trapped Gas and Foam Generation Mechanisms

The mobility of gas is greatly reduced when the injected gas is foamed. The reduction in gas mobility is attributed to the reduction in gas relative permeability and the increase in gas effective viscosity. The reduction in the gas relative permeability is a consequence of the larger amount of gas trapped when foam is present while the increase in gas effective viscosity is explicitly a function of foam texture. Therefore, understanding how foam is generated and subsequent trapped foam behavior is of paramount importance to modeling of gas mobility. In this paper, we push the envelope to enlighten our decisions of which descriptions are most physical to foam flow in porous media regarding both the flowing foam fraction and the rate of generation. We use a statistical pore network interwoven with the invasion percolation with memory algorithm to model foam flow as a drainage process and investigate the dependence of the flowing foam fraction on the pressure gradient and to shed light on foam generation mechanisms. A critical snap-off probability is required for strong foam to emerge in our network. The pressure gradient and, hence, the gas mobility reduction are very low below this critical snap-off probability. Above this snap-off probability threshold, we find that the steady-state flowing lamellae fraction scales as $$(\nabla \tilde{p})^{0.19}$$ in 2D lattices and as $$(\nabla \tilde{p})^{0.32}$$ in 3D lattices. Results obtained from our network were convolved with percolation network scaling ideas to compare the probabilities of snap-off and lamella division mechanisms in the network during the initial gas displacement at the leading edge of the gas front. At this front, during strong foam flow, lamella division is practically nonexistent in 2D lattices. In 3D lattices, lamella division occurs, but the probability of snap-off is always greater than the probability of lamella division.

Developmental Diversity in Cell Division Mechanisms

Cytokinesis is the subject of intense study, but mechanisms underlying contractility and cell shape change in cytokinesis are still being defined. Furthermore, it is unknown how contractile mechanisms vary among cell types and throughout development. Recent findings uncover differential molecular requirements for cytokinesis depending on cell fate and embryonic context.

How do plastids and mitochondria divide?

Plastids and mitochondria are thought to have originated from free-living cyanobacterial and alpha-proteobacterial ancestors, respectively, via endosymbiosis. Their evolutionary origins dictate that these organelles do not multiply de novo but through the division of pre-existing plastids and mitochondria. Over the past three decades, studies have shown that plastid and mitochondrial division are performed by contractile ring-shaped structures, broadly termed the plastid and mitochondrial-division machineries. Interestingly, the division machineries are hybrid forms of the bacterial cell division system and eukaryotic membrane fission system. The structure and function of the plastid and mitochondrial-division machineries are similar to each other, implying that the division machineries evolved in parallel since their establishment in primitive eukaryotes. Compared with our knowledge of their structures, our understanding of the mechanical details of how these division machineries function is still quite limited. Here, we review and compare the structural frameworks of the plastid and mitochondrial-division machineries in both lower and higher eukaryotes. Then, we highlight fundamental issues that need to be resolved to reveal the underlying mechanisms of plastid and mitochondrial division. Finally, we highlight related studies that point to an exciting future for the field.

Beata Mierzwa: Bridging the divide between science and art.

Mierzwa studies mechanisms of cell division in different cell types and tissue contexts.

Induction of rod versus cone photoreceptor-specific progenitors from retinal precursor cells

During development, multipotent progenitors undergo temporally-restricted differentiation into post-mitotic retinal cells; however, the mechanisms of progenitor division that occurs during retinogenesis remain controversial. Using clonal analyses (lineage tracing and single cell cultures), we identify rod versus cone lineage-specific progenitors derived from both adult retinal stem cells and embryonic neural retinal precursors. Taurine and retinoic acid are shown to act in an instructive and lineage-restricted manner early in the progenitor lineage hierarchy to produce rod-restricted progenitors from stem cell progeny. We also identify an instructive, but lineage-independent, mechanism for the specification of cone-restricted progenitors through the suppression of multiple differentiation signaling pathways. These data indicate that exogenous signals play critical roles in directing lineage decisions and resulting in fate-restricted rod or cone photoreceptor progenitors in culture. Additional factors may be involved in governing photoreceptor fates in vivo.

A novel combined model based on echo state network for multi-step ahead wind speed forecasting: A case study of NREL

Accurate wind speed forecasting plays a crucial role in wind power plants and wind systems. Numerous studies that dedicated to enhance wind speed forecasting accuracy have been proposed. Nevertheless, some classical models are not good at dealing with nonlinear time sequence, and artificial intelligence are easy fall into local optimum. Based on this, this paper proposed a novel combined model for wind speed forecasting, which combined hybrid models based on decomposition method and optimization algorithm. In this approach, four distinct hybrid models are proposed and to additionally enhance the forecasting performance, ESN (Echo state network) is initially applied to integrate all the results obtained by each hybrid model and achieve the ultimate forecasting results. Besides, a distinct data set division mechanism is adopted in the multi-step wind speed forecasting. To verify the effectiveness and versatility of the proposed combined model, the wind speed data of 20 m, 50 m, 80 m per minute of the M2 tower from the National Wind Power Technology Center, United States, are utilized as case studies. The experimental results indicate that the proposed combined model performs better than other conventional methods.

Dissecting the Control Mechanisms for DNA Replication and Cell Division in E. coli

Understanding the classic problem of how single E.coli cells coordinate cell division with genome replication would open the way to addressing cell-cycle progression at the single-cell level. Recent studies produced new data, but the contrast in their conclusions and proposed mechanisms makes the emerging picture fragmented and unclear. Here, we re-evaluate available data and models, including generalizations based on the same assumptions. We show that although they provide useful insights, none of the proposed models captures all correlation patterns observed in data. We conclude that the assumption that replication is the bottleneck process for cell division is too restrictive. Instead, we propose that two concurrent cycles responsible for division and initiation of DNA replication set the time of cell division. This framework allows us to select a nearly constant added size per origin between subsequent initiations as the most likely mechanism setting initiation of replication.

Emerging mechanisms of asymmetric stem cell division

The asymmetric cell division of stem cells, which produces one stem cell and one differentiating cell, has emerged as a mechanism to balance stem cell self-renewal and differentiation. Elaborate cellular mechanisms that orchestrate the processes required for asymmetric cell divisions are often shared between stem cells and other asymmetrically dividing cells. During asymmetric cell division, cells must establish asymmetry/polarity, which is guided by varying degrees of intrinsic versus extrinsic cues, and use intracellular machineries to divide in a desired orientation in the context of the asymmetry/polarity. Recent studies have expanded our knowledge on the mechanisms of asymmetric cell divisions, revealing the previously unappreciated complexity in setting up the cellular and/or environmental asymmetry, ensuring binary outcomes of the fate determination. In this review, we summarize recent progress in understanding the mechanisms and regulations of asymmetric stem cell division.

Toxoplasma gondii chromosomal passenger complex is essential for the organization of a functional mitotic spindle: a prerequisite for productive endodyogeny.

The phylum Apicomplexa encompasses deadly pathogens such as malaria and Cryptosporidium. Apicomplexa cell division is mechanistically divergent from that of their mammalian host, potentially representing an attractive source of drug targets. Depending on the species, apicomplexan parasites can modulate the output of cell division, producing two to thousands of daughter cells at once. The inherent flexibility of their cell division mechanisms allows these parasites to adapt to different niches, facilitating their dissemination. Toxoplasma gondii tachyzoites divide using a unique form of cell division called endodyogeny. This process involves a single round of DNA replication, closed nuclear mitosis, and assembly of two daughter cells within a mother. In higher Eukaryotes, the four-subunit chromosomal passenger complex (CPC) (Aurora kinase B (ARKB)/INCENP/Borealin/Survivin) promotes chromosome bi-orientation by detaching incorrect kinetochore-microtubule attachments, playing an essential role in controlling cell division fidelity. Herein, we report the characterization of the Toxoplasma CPC (Aurora kinase 1 (Ark1)/INCENP1/INCENP2). We show that the CPC exhibits dynamic localization in a cell cycle-dependent manner. TgArk1 interacts with both TgINCENPs, with TgINCENP2 being essential for its translocation to the nucleus. While TgINCENP1 appears to be dispensable, interfering with TgArk1 or TgINCENP2 results in pronounced division and growth defects. Significant anti-cancer drug development efforts have focused on targeting human ARKB. Parasite treatment with low doses of hesperadin, a known inhibitor of human ARKB at higher concentrations, phenocopies the TgArk1 and TgINCENP2 mutants. Overall, our study provides new insights into the mechanisms underpinning cell cycle control in Apicomplexa, and highlights TgArk1 as potential drug target.

Cellular aspect ratio and cell division mechanics underlie the patterning of cell progeny in diverse mammalian epithelia.

Cell division is essential to expand, shape, and replenish epithelia. In the adult small intestine, cells from a common progenitor intermix with other lineages, whereas cell progeny in many other epithelia form contiguous patches. The mechanisms that generate these distinct patterns of progeny are poorly understood. Using light sheet and confocal imaging of intestinal organoids, we show that lineages intersperse during cytokinesis, when elongated interphase cells insert between apically displaced daughters. Reducing the cellular aspect ratio to minimize the height difference between interphase and mitotic cells disrupts interspersion, producing contiguous patches. Cellular aspect ratio is similarly a key parameter for division-coupled interspersion in the early mouse embryo, suggesting that this physical mechanism for patterning progeny may pertain to many mammalian epithelia. Our results reveal that the process of cytokinesis in elongated mammalian epithelia allows lineages to intermix and that cellular aspect ratio is a critical modulator of the progeny pattern.

Division of Labor: How Microbes Split Their Responsibility

Within a biofilm, individual cells might perform only a subset of activities required for overall success of the biofilm. A new study examining matrix production, a task necessary for biofilm formation, shows possible mechanisms of genetic or phenotypic division of labor.

Cell scientist to watch – Guangshuo Ou

ABSTRACT Guangshuo moved from China to the USA in 2001 for his PhD at the University of California, Davis. There, he worked on motor proteins in ciliogenesis in C. elegans in the laboratory of Jonathan Scholey. He then joined the laboratory of Ron Vale at the University of California, San Francisco, and started to develop tools to investigate the mechanisms of neuroblast division, migration and differentiation in C. elegans larvae. Guangshuo returned to China in 2011 to establish his own research group at the Institute of Biophysics at the Chinese Academy of Sciences with a Junior One Thousand Talent Plan Award. Two years later, he moved to the School of Life Sciences at Tsinghua University in Beijing, and he became a principal investigator of the Joint Center for Life Sciences at Tsinghua and Peking Universities. Guangshuo became a Journal of Cell Science Editor in 2017. His laboratory continues to investigate the mechanisms regulating neural progenitors in C. elegans, using live-imaging, biochemical and genetic tools.

A Decrease in the Proliferative Activity of Human Mesenchymal Stem Cells during Long-Term Cultivation is Not Connected with Change in Their Migration Properties

In the context of rehabilitation therapy, the proliferation and migration of mesenchymal stem cells (MSCs) are functional properties of which the relationship remains unstudied. The aim of the present work consisted in parallel determination of proliferative and migration capacity of endometrial, adipose, and bonemarrow human MSCs (hMSCs) during long-term cultivation. The migration capacity of hMSCs was determined in comparison with those in epithelial cells of the established НСТ116, MCF7, and A-549 human lines. hMSCs obtained from different tissues demonstrate a comparable division rate on early passages, which progressively slows down by the tenth passage, which corresponds to a decrease in the expression of Ki67 proliferation marker and D1 cyclin. The mobility of MSCs during the determination of the cell migration through 8-μm filters and a “scratch regeneration” method does not change by the tenth passage. A high level of N-cadherin, vimentin production, and absence of E-cadherin, which level out in epithelial cells of the HCT116, MCF7, and A-549 lines is inverted as compared with those in MSCs, corresponding to the active mobility of MSCs of different tissue origin. Our results demonstrate that a decrease of the proliferative activity of MSCs of different tissue specificity during passaging is not associated with changes in their ability to migrate. It is likely that the mechanisms of division and cell-mobility regulation are genetically and functionally not related to each other and change autonomously during continuous cultivation.

Polyspermy produces viable haploid/diploid mosaics in sturgeon.

Most of sturgeon species (Acipenseridae) are currently critically endangered. Attempts to revive these populations include artificial breeding in hatcheries. However, under artificial reproduction, sturgeon embryos occasionally develop atypically, showing 3, 5, 6, 7, 9, or 10 cells at the 2- to 4-cell stage. This study was undertaken with the objective of understanding the mechanism of the atypical division (AD) in embryos during artificial breeding. Using several sturgeon species, we tested two hypotheses: (1) polyspermy and (2) retention of the second polar body. We found that (1) AD embryos survive similar to controls, (2) the ratio of AD embryos is positively correlated with the amount of sperm used for fertilization, (3) the number of micropyles and the area covered by them in AD embryos is significantly greater when compared to controls, (4) numerous spermatozoa nuclei are in the cytoplasm after fertilization, (5) all AD embryos are mosaics, and (6) AD fishes with n/2n ploidy contain diploid cells from maternal and paternal genetic markers, while the haploid cells contained only paternal ones. These results clearly indicate that AD embryos arise from plasmogamy where the accessory spermatozoon/spermatozoa entry the egg and develop jointly with zygotic cells. This suggests that a well-controlled fertilization procedure is needed to prevent the production of sturgeon with irregular ploidy, which can have detrimental genetic effects on sturgeon populations. On the other hand, if AD fish can produce haploid-derived clonal gametes, induction of multiple-sperm mosaicism might be a useful tool for the rapid production of isogenic strains of sturgeons.

Research progress on the asymmetric division in mammalian oocytes

The mammalian oocyte maturation process consists of two consecutive asymmetric divisions, and produces three daughter cells of vastly different sizes: one larger egg cell and two smaller polar bodies. Asymmetric division is a typical feature of mammalian oocyte meiosis that results in a highly polar egg cell. The mitosis of the cell after fertilization exhibits restored symmetric division, but the polarity characteristics formed during meiosis of oocytes are preserved and affect the polarity of early embryos. In this review, we summarize the research progress on asymmetric division of mammalian oocytes in recent years, and mainly focus on the asymmetric division of cytoplasmic and the asymmetric division of nucleus, including the functions of chromosome and cytoskeleton in asymmetric division of mammalian oocytes, the redistribution of cytoplasmic organelles occurring in oocyte maturation, and chromosome nonrandom separation. We aim to demonstrate the main mechanism of asymmetry division in mammalian oocytes from both cellular and molecular levels.

Stable Regulation of Cell Cycle Events in Mycobacteria: Insights From Inherently Heterogeneous Bacterial Populations.

Model bacteria, such as E. coli and B. subtilis, tightly regulate cell cycle progression to achieve consistent cell size distributions and replication dynamics. Many of the hallmark features of these model bacteria, including lateral cell wall elongation and symmetric growth and division, do not occur in mycobacteria. Instead, mycobacterial growth is characterized by asymmetric polar growth and division. This innate asymmetry creates unequal birth sizes and growth rates for daughter cells with each division, generating a phenotypically heterogeneous population. Although the asymmetric growth patterns of mycobacteria lead to a larger variation in birth size than typically seen in model bacterial populations, the cell size distribution is stable over time. Here, we review the cellular mechanisms of growth, division, and cell cycle progression in mycobacteria in the face of asymmetry and inherent heterogeneity. These processes coalesce to control cell size. Although Mycobacterium smegmatis and Mycobacterium bovis Bacillus Calmette-Guérin (BCG) utilize a novel model of cell size control, they are similar to previously studied bacteria in that initiation of DNA replication is a key checkpoint for cell division. We compare the regulation of DNA replication initiation and strategies used for cell size homeostasis in mycobacteria and model bacteria. Finally, we review the importance of cellular organization and chromosome segregation relating to the physiology of mycobacteria and consider how new frameworks could be applied across the wide spectrum of bacterial diversity.