Mechanical Forces Program the Orientation of Cell Division during Airway Tube Morphogenesis

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Quantitative Analyses of Cell Division in Plants

At the molecular level regulatory interactions between cell cycle genes are being uncovered rapidly, but less progress is made in unravelling how these molecular events regulate growth processes at the level of cells and of the whole organism. The main obstacle is the absence of a set of analytical tools that are powerful enough to determine pertinent parameters and, at the same time, relatively easy to use by non-specialized laboratories. Appropriate methodology to obtain this type of data has been pioneered in the first half of the last century and is now commonly defined as ‘kinematic analysis’. Unfortunately, the laborious nature of these analyses and the relatively complex numerical methods used, have limited their use to only a handful of specialized research groups. In this article we attempt to present an accessible entry to this methodology, particularly in terms of the mathematical framework. We start describing the simplest possible system, i.e., a virtually homogenous cell suspension culture. Then, we outline the analysis of dicotyledonous leaves, root tips, monocotyledonous leaves, and finally shoot apical meristems. For each of these systems we discuss the details of the calculation of cell division parameters such as cell cycle duration, size of the meristem and number of cells contained in it, which enables answering fundamental questions about the relative contribution of differences in cell production and cell size to variation in growth. In addition, we discuss the assumptions and limitations of these and alternative methodologies with the aim to facilitate the choice of appropriate analyses depending on the specific research question.     

细胞不对称分裂

细胞不对称分裂是多细胞生物发育的基础。细胞不对称分裂的重要特征是细胞命运决定子在细胞分裂期间的不对称分离。细胞不对称分裂一般要经历4个步骤：在细胞中建立一个极性轴;沿此轴定向并形成纺锤体;细胞命运决定子沿极性轴作极性分布;细胞分裂后,不同的细胞命运决定子指导决定细胞的不同命运。     

The Bacterial Cell Cycle: DNA Replication,Nucleoid Segregation,and Cell Division

Data on the bacterial cell cycle published in the last 10–15 years are considered, with a special stress on studies of nucleoid segregation between dividing cells. The degree of similarity between the eukaryotic mitotic apparatus and the apparatus performing nucleoid separation is discussed.__________Translated from Mikrobiologiya, Vol. 74, No. 4, 2005, pp. 437–451.Original Russian Text Copyright © 2005 by Prozorov.     

B细胞不对称分裂

细胞的不对称分裂对于细胞多样性产生的重要性已经被大部分人所认识。B细胞的不对称分裂首先是在抗体类别转换的研究中发现的。最近,美国5科学家对B细胞在免疫发生中心中不对称分裂的原因进行了探索。结果发表在2012年1月20日出版的《Science》中。B细胞的不对称分裂参与体液免疫的抗体类别转换和抗体亲和力成熟过程。对于其机制仍不清楚,但目前研究初步提示细胞内分子的不对称分布是其发生的上游因素。并且B细胞的不对称分裂可能与不对称抗原分离可能在抗体亲和力成熟过程中具有独立协同作用。     

生长素对拟南芥叶片发育调控的研究进展

叶片（包括子叶）是茎端分生组织产生的第一类侧生器官,在植物发育中具有重要地位。早期叶片发育包括三个主要过程：叶原基的起始,叶片腹背性的建立和叶片的延展。大量证据表明叶片发育受到体内遗传机制和体外环境因子的双重调节。植物激素,尤其是生长素在协调体内外调节机制中起着不可或缺的作用。生长素的稳态调控、极性运输和信号转导影响叶片发育的全过程。本文着重介绍生长素在叶片生长发育和形态建成中的调控作用,试图了解复杂叶片发育调控网络。     

Cortical and Nuclear Events During Cell Division and Resting Cyst Formation in Colpoda inflata

Nuclear and cortical phenomena during dividing and resting cyst formation of Colpoda inflata are described. Cell division forms a cyst and produces two or four tomites. In each tomite, the right oral field results from the proliferation of the anterior extreme of a single kinety, and the left oral field results from the proliferation of four, five, or six somatic kineties. After macronuclear division, each macronuclear mass undergoes a chromatinic extrusion process. During resting cyst formation, the oral infraciliature of the vegetative cell is resorbed. The somatic kineties dispose in a radial way and some pairs of kinetosomes disappear. As in cell division, there is an extrusion process. From these results we conclude that the resting cysts of Colpoda inflata cannot be included in any group of the previous classifications for hypotrich resting cysts. Thus, we propose a new additional group to Walker and Maugel's classification called PKR (partial-kinetosome-resorbing) cysts.     

Cytokinin-Regulated Mesophyll Cell Division and Expansion during Development of Cucurbita pepo Leaves

The role of cytokinins in the development of mesophyll structure was studied in developing pumpkin Cucurbita pepo L. leaves. Leaves were treated with cytokinins at different stages of growth: when they reached 25 or 50% of their final size (S _max), immediately after leaf growth ceased, and during senescence. At the early stages of leaf development, treatment with exogenous benzyladenine accelerated division of mesophyll cells. At the later stages of development, BA treatment activated expansion of growing cells and those, which have just accomplished their growth. The exogenous cytokinin did not affect the senescent leaf cells. The content of endogenous cytokinins changed during mesophyll development. The juvenile leaves (25% of S _max) were characterized by low level of these phytohormones. In the expanding leaves (50% of S _max), the content of phytohormones increased and decreased when leaf growth ceased. In the senescent leaves, the cytokinin content decreased markedly. It was concluded that the response of mesophyll cells to cytokinin depended on the cell growth phase at the moment of hormone action. Furthermore, in the young leaves, lower cytokinin concentrations were required for division of mesophyll cells in vivo than for cell expansion at the final stage of leaf development.     

The Roles of Cell Division and Cell Expansion in the Growth of Alfalfa Leaf Mesophyll

Leaf mesophyll of Medicago sativa (L.) was investigated to determinethe roles of cell division and cell expansion in tissue growth.Samples of leaf tissue were macerated, stained, and squashed.The slides were studied under a phase microscope to determinethe percentage of recently divided cells and the average celldiameter for leaflets of varying lengths. Cell division wasgreatest in young leaflets and virtually ceased as a leaf lengthof 12 mm was attained. For leaflets less than 12 mm in length,the rate of increase in cell size appeared to be inversely associatedto the degree of cell division. For alfalfa leaflets greaterthan 12 mm in length, the mean cell size increased in proportionto leaf length since cell division had virtually ceased.     

Host-Polarized Cell Growth in Animal Symbionts

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CPPU对瓠瓜单性结实的诱导作用及对细胞分裂和内源激素水平的影响

NAA和GA3处理未经授粉的瓠瓜子房不能显著促进其细胞分裂和膨大而产生单性结实果,而CP-PU处理未经授粉的瓠瓜子房则使其细胞数目和中果皮单个细胞横切面积以及单果重都显著高于未授粉和人工授粉果.经CPPU诱导座果而产生的单性结实果中IAA、ABA和t-zeatin的浓度均不同程度地低于人工授粉和不授粉果实.     

Ectopic BASL Reveals Tissue Cell Polarity throughout Leaf Development in Arabidopsis thaliana

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丛藓科（Pottiaceae）植物叶细胞形态特征及其系统学意义

通过光学显微镜（LM）和扫描电镜（SEM）观察了17属国产丛藓科（Pottiaceae）植物叶中上部细胞的形态特征,结果表明：丛藓科植物的叶中上部细胞的形状、大小及表面形态等特征上具较大相似性;据细胞表面特征,叶细胞可分为无疣或具乳突、具圆疣以及具分枝的马蹄形疣3种类型,且该特征在丛藓科不同属、种间有较大的区别。因此,叶细胞形态特征可为丛藓科植物属级和亚科级的划分提供细胞形态学依据。     

Decoupling of Nuclear Division Cycles and Cell Size during the Coenocytic Growth of the Ichthyosporean Sphaeroforma arctica

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Characterization of Hormonal Complex in Pea Phenotypes Differing in Leaf Morphology

Two genotypes of the pea (Pisum sativum L.) with wild-type leaves (variety Orlovchanin, Af/Af genotype) and the afila morphotype (aphyllous variety Nord, af/af genotype) were compared in terms of growth performance and hormonal characteristics of different leaf parts and the whole plant. The replacement of leaflets by tendrils in the afila variety led to a reduction in total dry weight and the area of photosynthesizing surfaces. The loss of leaflets was partly compensated for by rapid expansion of stipules at early stages of plant development and by the hypertrophy of tendrils at later stages. The excessive development of stipules in afila plants was paralleled by the increase in IAA and cytokinin level in their tissues. The hypertrophied development of tendrils and chlorophyll accumulation in tendrils of afila plants was correlated with a high IAA and cytokinin content at a low ABA background level. The elevated content of ABA in tissues of wild-type plants was associated with the preferential development of leaflets and a larger transpiratory surface compared with those in the afila form. It is assumed that this feature ensures the turgescence of wild-type plants. The possible involvement of phytohormones in growth and morphogenesis of pea mutants is discussed.     

利用流式细胞仪研究拟南芥叶发育过程中细胞周期的调控

叶的形态建成依赖于细胞不断地分裂增殖和不同类型细胞的特化。在叶发育早期,叶细胞主要通过旺盛的有丝分裂来增加原基中细胞的数目。随着叶片的生长,叶细胞自顶部向基部逐渐退出有丝分裂进入内复制来增加细胞的倍性,同时伴随细胞的扩展和分化。本文介绍利用流式细胞仪研究双子叶模式植物拟南芥叶发育过程中细胞周期调控的方法和具体研究实例。我们发现至少存在3种类型的细胞周期异常的拟南芥叶发育突变体。此外,我们还介绍利用流式细胞仪测定DNA复制效率的方法。     

Division competence in Tetrahymena: determination of minimum cell volume and rate of nutrient uptake

Cell volume and doubling time have been determined for exponentially growing Tetrahymena pyriformis cells in broth medium with and without glucose and in media made from these media by dilution with water. The cells tolerate media with dry weights from 105 down to 0.06 g/L. In the diluted media the cells have small volumes and the doubling time is increased. When the cell volume increase per time per cell in a given medium is expressed as a function of the cell volume in this same medium, a direct proportionality is found. From this equation the minimum cell volume of division competence (MVDC) can be found. It is 2,100 microns 3 for T. pyriformis at 28 degrees C. The lag period resulting from an upshift of exponentially growing cells from diluted media to more concentrated media is a function of the initial and resulting cell volumes and MVDC. The increase in cell volume per unit of time for a given cell depends on the dry weight of the medium. This parameter can be transformed to mass increase per cell surface area per time, which represents rate of nutrient uptake. When plotted against the dry weight of the media, a Michaelis-Menten-like curve is obtained with two Km values of 3.8 and 0.08 g/L with corresponding Vmax values of 20 and 4 ng/cm2.s. The low Km value (0.08 g/L) indicates that Tetrahymena is able to take up nutrients from highly diluted media. The high value of Vmax (20 ng/cm2.s) increases the ability of growth in more concentrated media.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transduction Mechanisms Involved in Thrombin Receptor-Induced Nerve Growth Factor Secretion and Cell Division in Primary Cultures of Astrocytes

Abstract: In astrocytes, thrombin and thrombin receptor-activating activating peptide (TRAP-14), a 14-amino-acid agonist of the proteolytic activating receptor for thrombin (PART), significantly increased cell division as assessed by [³H]thymidine incorporation into DNA (EC₅₀ = 1 n M and +650% at 100 n M for thrombin; EC₅₀ = 3 µ M and +600% at 100 µ M for TRAP-14) and nerve growth factor (NGF) secretion (approximately twofold at 100 n M thrombin or 100 µ M TRAP-14). The [³H]thymidine incorporation was prevented by protein kinase C inhibitors (staurosporine and H7) or by down-regulation of this enzyme by chronic exposure of astrocytes to phorbol 12-myristate 13-acetate (PMA). Thrombin-induced NGF secretion was completely inhibited by protein kinase C inhibitors. Treatment with PMA stimulated NGF secretion 19-fold, and this effect was not further enhanced by thrombin. These data suggest an absolute requirement of protein kinase C activity for thrombin-induced NGF secretion and cell division. Pretreatment of astrocytes with pertussis toxin (PTX) reduced thrombin- and TRAP-14-induced DNA synthesis. PART activation caused a decrease in forskolin-stimulated cyclic AMP accumulation. PTX treatment prevented the inhibitory effect of PART activation on cyclic AMP accumulation, suggesting that a PTX-sensitive G protein, such as G_i or G_o, is involved in thrombin-induced cell division. In contrast, thrombin-induced NGF secretion was not inhibited by PTX. Finally, the protein tyrosine kinase inhibitor herbimycin A partially but significantly prevented thrombin- and TRAP-14-induced cell division but was without effect on NGF secretion. Taken together, these results demonstrate that, in astrocytes, PART(s)-triggered cell division or NGF secretion is mediated by distinct transduction mechanisms.