Cycling in a crowd: Coordination of plant cell division,growth, and cell fate

The reiterative organogenesis that drives plant growth relies on the constant production of new cells, which remain encased by interconnected cell walls. For these reasons, plant morphogenesis strictly depends on the rate and orientation of both cell division and cell growth. Important progress has been made in recent years in understanding how cell cycle progression and the orientation of cell divisions are coordinated with cell and organ growth and with the acquisition of specialized cell fates. We review basic concepts and players in plant cell cycle and division, and then focus on their links to growth-related cues, such as metabolic state, cell size, cell geometry, and cell mechanics, and on how cell cycle progression and cell division are linked to specific cell fates. The retinoblastoma pathway has emerged as a major player in the coordination of the cell cycle with both growth and cell identity, while microtubule dynamics are central in the coordination of oriented cell divisions. Future challenges include clarifying feedbacks between growth and cell cycle progression, revealing the molecular basis of cell division orientation in response to mechanical and chemical signals, and probing the links between cell fate changes and chromatin dynamics during the cell cycle.

Plant cell cycle and division are linked to specific cell fates and respond to growth-related cues, such as metabolic state, cell size, cell shape, and mechanical stress.     

Action potential conduction between a ventricular cell model and an isolated ventricular cell.

We used the Luo and Rudy (LR) mathematical model of the guinea pig ventricular cell coupled to experimentally recorded guinea pig ventricular cells to investigate the effects of geometrical asymmetry on action potential propagation. The overall correspondence of the LR cell model with the recorded real cell action potentials was quite good, and the strength-duration curves for the real cells and for the LR model cell were in general correspondence. The experimental protocol allowed us to modify the effective size of either the simulation model or the real cell. 1) When we normalized real cell size to LR model cell size, required conductance for propagation between model cell and real cell was greater than that found for conduction between two LR model cells (5.4 nS), with a greater disparity when we stimulated the LR model cell (8.3 +/- 0.6 nS) than when we stimulated the real cell (7.0 +/- 0.2 nS). 2) Electrical loading of the action potential waveform was greater for real cell than for LR model cell even when real cell size was normalized to be equal to that of LR model cell. 3) When the size of the follower cell was doubled, required conductance for propagation was dramatically increased; but this increase was greatest for conduction from real cell to LR model cell, less for conduction from LR model cell to real cell, and least for conduction from LR model cell to LR model cell. The introduction of this "model clamp" technique allows testing of proposed membrane models of cardiac cells in terms of their source-sink behavior under conditions of extreme coupling by examining the symmetry of conduction of a cell pair composed of a model cell and a real cardiac cell. We have focused our experimental work with this technique on situations of extreme uncoupling that can lead to conduction block. In addition, the analysis of the geometrical factors that determine success or failure of conduction is important in the understanding of the process of discontinuous conduction, which occurs in myocardial infarction.     

Cell motility in a new single-cell wound model

Summary  Until now researchers have used a monolayer of cultured cells to investigate cell motility toward an injured cell. However, we suspect that, when using this method, adjacent cells move to the free space due to relief of contact inhibition. The current study was designed to investigate the cell motility nearby an injured cell in varying cell connectivity. A lowpower laser beam was used to damage one cell selectively with the silver coating beads. After injury, we observed the cell motility in three different cell types: (1) those immediately adjacent to the injured cell, 92) those removed from the injured cell by interposition of another cell, and (3) those removed from the injured cell by free space. The cells that are in direct contact with the injured cell moved toward the injured cell within 1.5–3.0 h. Indirectly connected cells and cells with no contact, on the other hand, showed no significant movement toward the injured cell. This suggests that the cell motility toward the cell injury is not only due to relief of contact inhibition but might also be caused by cell-to-cell signaling via cell connection. The current method will provide a tool to create a cell injury without damaging adjacent cells.     

Unlinked regulation of cell growth and differentiation in immature B cell lines

We established many immunoglobulin-null immature B cell lines transformed by tsOS-59, a temperature-sensitive mutant of Abelson murine leukemia virus. In different cell lines cell growth was depressed and cell differentiation (generation of intracytoplasmic mu-positive cells from Ig- cells) was induced by the shift of culture temperature from low (35 degrees C) to high (39 degrees C). Cell lines were categorized into four groups: (i) temperature sensitive (ts) to both cell growth and differentiation, (ii) ts to cell growth but not to cell differentiation, (iii) ts to cell differentiation but not to cell growth, and (iv) ts to neither cell growth nor differentiation. These results indicated that the depression of cell growth did not necessarily induce cell differentiation, and that cell differentiation was induced regardless of whether cell growth was depressed or not. Furthermore, the results showed that the depression of cell growth and the induction of cell differentiation occurred without the reduction of tyrosine kinase activity of P120gag-abl at high, nonpermissive temperature. Our cell growth and differentiation system described here should provide us with the interesting findings of the relation between B cell growth and differentiation.     

Three-Dimensional Numerical Model of Cell Morphology during Migration in Multi-Signaling Substrates

Cell Migration associated with cell shape changes are of central importance in many biological processes ranging from morphogenesis to metastatic cancer cells. Cell movement is a result of cyclic changes of cell morphology due to effective forces on cell body, leading to periodic fluctuations of the cell length and cell membrane area. It is well-known that the cell can be guided by different effective stimuli such as mechanotaxis, thermotaxis, chemotaxis and/or electrotaxis. Regulation of intracellular mechanics and cell’s physical interaction with its substrate rely on control of cell shape during cell migration. In this notion, it is essential to understand how each natural or external stimulus may affect the cell behavior. Therefore, a three-dimensional (3D) computational model is here developed to analyze a free mode of cell shape changes during migration in a multi-signaling micro-environment. This model is based on previous models that are presented by the same authors to study cell migration with a constant spherical cell shape in a multi-signaling substrates and mechanotaxis effect on cell morphology. Using the finite element discrete methodology, the cell is represented by a group of finite elements. The cell motion is modeled by equilibrium of effective forces on cell body such as traction, protrusion, electrostatic and drag forces, where the cell traction force is a function of the cell internal deformations. To study cell behavior in the presence of different stimuli, the model has been employed in different numerical cases. Our findings, which are qualitatively consistent with well-known related experimental observations, indicate that adding a new stimulus to the cell substrate pushes the cell to migrate more directionally in more elongated form towards the more effective stimuli. For instance, the presence of thermotaxis, chemotaxis and electrotaxis can further move the cell centroid towards the corresponding stimulus, respectively, diminishing the mechanotaxis effect. Besides, the stronger stimulus imposes a greater cell elongation and more cell membrane area. The present model not only provides new insights into cell morphology in a multi-signaling micro-environment but also enables us to investigate in more precise way the cell migration in the presence of different stimuli.     

东亚飞蝗Locusta migratoria manilensis（Mey．）膝下器中具橛感器的附属细胞和附属结构的超微结构

东亚飞蝗膝下器的具橛感器主要由三类细胞组成．即：感觉细胞、感橛细胞和冠细胞。感觉细胞为具橛感器的主要结构和功能细胞,其超微结构已在其他的文章中描述。感橛细胞是具橛感器的主要支持细胞,从近端到远端依次与神经胶质细胞、感觉细胞的远端树突部分和感觉纤毛部以及顶端细胞外结构——冠、冠细胞直接接触．感橛细胞内最明显的结构为感概,另外,感橛细胞质被高度“空化”。冠细胞紧密包围着感橛细胞和冠,冠细胞中含有大量的纵行微管．并将整个具橛感器连接到体壁上。     

Construction of a cultivation system of a yeast single cell in a cell chip microchamber

A novel single cell screening system was constructed using a yeast cell chip in combination with the yeast cell surface engineering [NanoBiotechnology 2005, 1, 105-111]. Enzymes or functional proteins displayed on a yeast cell surface can be used as a protein cluster. To achieve high-throughput screening of protein libraries on the cell surface, a catalytic reaction by a single cell-surface-engineered yeast cell was successfully carried out in the microchamber on the yeast cell chip. After screening, to replicate a target cell for use in measuring of activity, DNA sequencing, and preservation, a novel single cell cultivation system in the yeast cell chip was constructed. To avoid damage of the rapid dry up of medium in the microchamber array, the yeast cell chip was modified with a protection sheet, so that the modified chip was like a micro-culture tank constructed on the yeast cell chip microchamber. As a result, single yeast cell cultivation in the yeast cell chip microchamber was observed, and the modified yeast cell chip was evaluated to be good for a single cell selection. The improvement showed that the single cell screening system coupled with the single cell cultivation using the modified yeast cell chip may be superior to that by a cell sorter for the isolation of a target cell and its practical use.     

樟子松大孢子的发生和雌配子体的形成过程

樟子松大孢子母细胞经一系列变化,发育成雌配子体。在哈尔滨地区樟子松大孢子母细胞于每年6月8～14日形成,接着进行减数分裂,于6月16～20日形成大孢子。随着大孢子核的分裂,进入游离核时期,并于次年5月28日～6月4日形成细胞壁,幼雌配子体中出现颈卵器原始细胞,它分裂一次形成颈细胞和中央细胞。6月7～9日中央细胞分裂成卵细胞和腹沟细胞,6月13～15日颈卵器发育成熟。成熟的颈卵器含有颈细胞、腹沟细胞和卵细胞,但颈细胞和腹沟细胞已经退化。     

Stacked stem cell sheets enhance cell-matrix interactions

Cell sheet engineering has enabled the production of confluent cell sheets stacked together for use as a cardiac patch to increase cell survival rate and engraftment after transplantation, thereby providing a promising strategy for high density stem cell delivery for cardiac repair. One key challenge in using cell sheet technology is the difficulty of cell sheet handling due to its weak mechanical properties. A single-layer cell sheet is generally very fragile and tends to break or clump during harvest. Effective transfer and stacking methods are needed to move cell sheet technology into widespread clinical applications. In this study, we developed a simple and effective micropipette based method to aid cell sheet transfer and stacking. The cell viability after transfer was tested and multi-layer stem cell sheets were fabricated using the developed method. Furthermore, we examined the interactions between stacked stem cell sheets and fibrin matrix. Our results have shown that the preserved ECM associated with the detached cell sheet greatly facilitates its adherence to fibrin matrix and enhances the cell sheet-matrix interactions. Accelerated fibrin degradation caused by attached cell sheets was also observed.     

Mitochondrial DNA molecules and virtual number of mitochondria per cell in mammalian cells

A new biochemical method for estimating the virtual number of mitochondria (mt) per cell was developed and used together with a plasmid probe to measure mt DNA/mitochondrion and mt DNA/cell. These methods were used in five cell types from four mammalian species. Mt DNA/mitochondrion was essentially constant in all cell types (mean 2.6 +/- 0.30 SE mitochondrial DNA molecules/mt). Mt DNA molecules/cell encompassed an eight-fold range between various cell types (low 220 +/- 6.2; high 1,720 +/- 162 mt DNA molecules/cell). Virtual mt number/cell ranged from 83 +/- 17 to 677 +/- 80 (SE) mt/cell in various cell types. All five mammalian virtual mitochondria contained the same genomic mass. The number of virtual mitochondria per cell and amount of mt DNA per cell appear to be closely regulated within a given cell type but differ widely from cell type to cell type.     

Butanol-extractable and detergent-solubilized cell surface components from murine large cell lymphoma cells associated with adhesion to organ microvessel endothelial cells.

Metastatic variant cell lines of the murine RAW117 large cell lymphoma were used to study the cell surface components involved in syngeneic tumor cell/microvessel endothelial cell interactions. Poorly liver-metastatic parental RAW117-P cell line adhered to murine hepatic sinusoidal endothelial cell monolayers at significantly lower rates than the liver-selected, highly liver-metastatic RAW117-H10 line and both cell lines were poorly adherent to lung microvessel and bovine aorta endothelial cells. Viable, 2% 1-butanol-treated RAW117-H10 tumor cells formed fewer liver tumor nodules in experimental metastasis assays than untreated H10 cells and were significantly less adherent to murine hepatic sinusoidal endothelial cell monolayers. When 2% 1-butanol extracts of metabolically labeled or CHAPS detergent lysates of cell surface-labeled tumor cells were analyzed for their ability to bind to fixed microvessel endothelial cell monolayers, quantitative differences were found in the extractable tumor cell surface components that bound to the different organ-derived microvessel endothelial cells. Cell surface components (1-butanol extractable), of Mr approximately 85,000-90,000 and approximately 37,000-40,000 bound to hepatic sinusoidal endothelial cell monolayers to a greater extent than to murine lung microvessel endothelial or bovine aortic endothelial cell monolayers, whereas tumor cell surface components of Mr approximately 45,000, approximately 33,000, and approximately 25,000 bound similarly to endothelial cells regardless of origin. The results suggest but do not prove that tumor cell/endothelial cell adhesion involves multiple tumor cell surface components, some of which commonly bind to various endothelial cells and others for which binding may be dictated by the tissue origin and type of endothelial cell. Particular RAW117 butanol-extractable cell membrane components were associated with tumor cell-endothelial cell adhesion, and these components could be responsible, in part, for the preferential adhesion of RAW117 cells to liver sinusoidal endothelial cells and metastasis to liver.     

Differential expression of the c-myb proto-oncogene marks the pre-B cell/B cell junction in murine B lymphoid tumors

A series of murine B lymphoid tumor cell lines which are representative of the pre-B cell, immature and mature B cell, and plasma cell stages of B cell development have been examined for expression of c-myb proto-oncogene mRNA. The pre-B cell lymphoma cell lines express equivalent high steady state levels of c-myb mRNA. In contrast, the B cell lymphoma and plasmacytoma cell lines express steady state c-myb mRNA at levels which are 0.005 to 0.1 times that of the pre-B cell lymphoma lines. These results correlate high levels of c-myb mRNA expression with the pre-B cell stage of development. Subclones of the 1881 pre-B cell lymphoma which express K light chain and are surface IgM-positive as well as two types of hybrid B lymphoid cell lines have been used to demonstrate that surface immunoglobulin expression is not sufficient to result in the down-regulation of c-myb mRNA levels or changes in the expression N-myc mRNA, lambda 5 mRNA, or the BP-1 surface antigen which are markers of the pre-B cell stage of development. Thus, changes in the expression of genes which are independent of immunoglobulin expression are associated with transition from the pre-B cell to the immature B cell stage of development.     

The relation of temperature and lipid composition to cell adhesion

We have examined as a function of temperature the effect of changes in the composition of the fatty acid chains of membrane phospholipids on the rate of cell to cell adhesion in the neuronal cell line B103. The rate of cell to cell adhesion in this cell line is highly temperature dependent but is not influenced by changes in the fatty acid composition of the plasma membrane generated by growing the cells either in the presence of oleic acid or elaidic acid. In contrast the temperature dependence of the rate of cell to cell adhesion, measured in a monolayer adhesion assay, is highly dependent on the shear force used during the assay. A two-step model of cell to cell adhesion involving multiple adhesion ligands is presented which can be used to explain these observations.     

CELL—CELL CONTACTS ACCELERATE CELL COLONY GROWTH IN SPARSE CULTURES OF CHICK EMBRYO FIBROBLASTS

There is no cell proliferation in very sparcely plated chick embryo cell cultures. Substituting conditioned medium or adding of ethanol-fixed homologous cells to the cultures accelerates cell colony growth. The mechanism for the mitogenic action of fixed cells is considered to be the contact stimulation of cell proliferation, and addition of extra cells to sparse culture is believed to mimic the cell micro-environment existing in subconfluent cultures. The role of diverse cell—cell contacts in cultured cell growth regulation is discussed. The procedure used (addition of ethanol-fixed cells) may improve normal cell cloning techniques.     

Linking cell division to cell growth in a spatiotemporal model of the cell cycle

Cell division must be tightly coupled to cell growth in order to maintain cell size, yet the mechanisms linking these two processes are unclear. It is known that almost all proteins involved in cell division shuttle between cytoplasm and nucleus during the cell cycle; however, the implications of this process for cell cycle dynamics and its coupling to cell growth remains to be elucidated. We developed mathematical models of the cell cycle which incorporate protein translocation between cytoplasm and nucleus. We show that protein translocation between cytoplasm and nucleus not only modulates temporal cell cycle dynamics, but also provides a natural mechanism coupling cell division to cell growth. This coupling is mediated by the effect of cytoplasmic-to-nuclear size ratio on the activation threshold of critical cell cycle proteins, leading to the size-sensing checkpoint (sizer) and the size-independent clock (timer) observed in many cell cycle experiments.     

艰难梭菌A毒素的细胞致死活性研究

本文报道艰难梭菌Ａ毒素对４种培养细胞的细胞致死活性的探讨。４种培养细胞为Ｖｅｒｏ（非洲绿猴肾细胞）细胞、ＴＰＣ─１（人甲状腺肿瘤细胞）细胞、ＮＩＨ３Ｔ３细胞（小鼠成纤维细胞）及将ｒａｓ癌基因转基因于ＮＩＨ３Ｔ３细胞的ＮＩＨ３Ｔ３ｒａｓ细胞。应用台酚蓝排除能试验、噻唑蓝（ＭＴＳ）比色、细胞膜损害测定试验、荧光显微术观察细胞核的形态变化等测定Ａ毒素细胞致死活性。实验表明：４种培养细胞系对Ａ毒素细胞圆缩化作用的敏感性依次为ＮＩＨ３Ｔ３ｒａｓ,ＴＰＣ─１,Ｖｅｒｏ,ＮＩＨ３Ｔ３细胞。而对Ａ毒素细胞致死活性的敏感性依次为ＴＰＣ─１,ＮＩＨ３Ｔ３,Ｖｅｒｏ,ＮＩＨ３Ｔ３ｒａｓ细胞。从而得知Ａ毒素的细胞致死活性不但依细胞种类不同而不同,而且也不一定与Ａ毒素的细胞圆缩化作用有关。肿瘤细胞ＴＰＣ─１细胞对Ａ毒素致死活性有特殊敏感性。以上结果对探索抗癌新药的研制具有重要意义。     

Pathways of apoptosis and importance in development

The elimination of cells by programmed cell death is a fundamental event in development where multicellular organisms regulate cell numbers or eliminate cells that are functionally redundant or potentially detrimental to the organism. The evolutionary conservation of the biochemical and genetic regulation of programmed cell death across species has allowed the genetic pathways of programmed cell death determined in lower species, such as the nematode Caenorhabditis elegans and the fruitfly Drosophila melanogaster to act as models to delineate the genetics and regulation of cell death in mammalian cells. These studies have identified cell autonomous and non-autonomous mechanisms that regulate of cell death and reveal that developmental cell death can either be a pre-determined cell fate or the consequence of insufficient cell interactions that normally promote cell survival.     

Subsidiary cells in the Orchidaceae: their general distribution with special reference to development in the Oncidieae

Subsidiary cell formation in leaves of the Oncidieae begins with the production of a trapezoid cell on each side of the guard cell mother cell. The trapezoid cells are formed by oblique divisions in the tiles of cells next to the tile of cells containing the guard cell mother cell. The trapezoid cell usually divides unequally to form a subsidiary cell and a derivative cell. The subsidiary cell is smaller and next to the guard cell mother cell. The derivative cell enlarges and is often indistinguishable from the other epidermal cells. Rarely, polar subsidiary cells are also formed. In very rare cases the smaller of the division products of the trapezoid cell divides to form two subsidiary cells next to each guard cell. Subsidiary cells have been found in all tribes of the epidendroid and vandoid groups, all neottoid tribes examined except the Orchideae, and the subfamily Cypripedioideae. The absence of subsidiary cells in primitive genera of the epidendroid tribes and the presence of subsidiary cells in the most advanced genera of the epidendroid and vandoid groups supports the hypothesis that the presence of subsidiary cells is an advanced condition in the Orchidaceae.     

Cell cycle traverse and protein metabolism in human NHIK 3025 cells: the role of anchorage

We have studied the effect of cell anchorage on the human cell line NHIK 3025 in vitro, to see whether the growth regulating effect of cell anchorage primarily affected DNA division cycle or mass growth cycle. It was found that cell to cell anchorage had the same effect on cell cycle progression as anchorage to a solid surface, which indicates that it is anchorage per se and not cell shape that is important for growth control in NHIK 3025 cells. When NHIK 3025 cells were grown without attachment to a solid surface, both G1 and cell cycle duration was prolonged by 6 h, which means that the prolonged cell cycle was due to a prolonged G1. During the first part of the cell cycle the rate of protein synthesis and degradation was constant, and at the same level in cells grown with and without attachment. This means that the prolonged G1 was not due to a reduced protein accumulation or mass growth. Towards the end of the cell cycle protein accumulation was reduced. This effect was either due to a size control before cell division or a secondary effect of the prolonged G1. We therefore conclude that cell anchorage as a growth regulator primarily affects the DNA/cell division cycle.     

Sialic acids in T cell development and function

Virtually all cell surface proteins and many cell membrane lipids are glycosylated, creating a cell surface glycocalyx. The glycan chains attached to cell surface glycoproteins and glycolipids are complex structures with specific additions that determine functions of the glycans in cell–cell communication and cell sensing of the environment. One type of specific modification of cell surface glycans is decoration of glycan termini by sialic acids. On T cells, these terminal sialic acid residues are involved in almost every aspect of T cell fate and function, from cell maturation, differentiation, and migration to cell survival and cell death. The roles that sialylated glycans play in T cell development and function, including binding to specific sialic acid-binding lectins, are reviewed here.