Mutants altered in the control co-ordinating cell division with cell growth in the fission yeast Schizosaccharomyces pombe

Summary The control co-ordinating cell division with cell growth has been investigated in the fission yeast Schizosaccharomyces pombe. Twenty-five mutants altered in this control have been isolated which have the same growth rate as wild type but divide at a smaller cell size. The mutants define two genes wee 1 and wee 2, both of which are involved in a control initiating mitosis when the cell attains a critical size.     

Stunted plant 1 mediates effects of cytokinin, but not of auxin, on cell division and expansion in the root of Arabidopsis

Plants control organ growth rate by adjusting the rate and duration of cell division and expansion. Surprisingly, there have been few studies where both parameters have been measured in the same material, and thus we have little understanding of how division and expansion are regulated interdependently. We have investigated this regulation in the root meristem of the stunted plant 1 (stp1) mutation of Arabidopsis, the roots of which elongate more slowly than those of the wild type and fail to accelerate. We used a kinematic method to quantify the spatial distribution of the rate and extent of cell division and expansion, and we compared stp1 with wild type and with wild type treated with exogenous cytokinin (1 microM zeatin) or auxin (30 nM 2,4-dichlorophenoxyacetic acid). All treatments reduced average cell division rates, which reduced cell production by the meristem. Auxin lowered root elongation by narrowing the elongation zone and reducing the time spent by a cell in this zone, but did not decrease maximal strain rate. In addition, auxin increased the length of the meristem. In contrast, cytokinin reduced root elongation by lowering maximal strain rate, but did not change the time spent by a cell within the elongation zone; also, cytokinin blocked the increase in length and cell number of the meristem and elongation zone. The cytokinin-treated wild type phenocopied stp1 in nearly every detail, supporting the hypothesis that cytokinin affects root growth via STP1. The opposite effects of auxin and cytokinin suggest that the balance of these hormones may control the size of the meristem.     

细胞分裂蛋白编码基因的敲除对丙酮丁醇梭菌溶剂合成与细胞形态的影响

丙酮丁醇梭菌是生物丁醇合成的重要菌株,近年来,研究者们利用基因编辑等技术对其进行菌株改造。通过对丙酮丁醇梭菌中3个细胞分裂蛋白(RodA、DivIVA、DivIB)编码基因(cac1251、cac2118、cac2125)进行敲除,发现cac2118敲除菌株的细胞在产溶剂期为球状形态,细胞变小,ABE发酵的丁醇得率为0.19 g/g,与野生型相比提高了5.6%。cac1251敲除菌株的葡萄糖消耗量和丁醇产量与野生型相比降低了33.9%和56.3%,分别为47.3 g/L和5.6 g/L。cac1251和cac2125的敲除对细胞生长有显著影响,菌体浓度最大值与野生型相比分别降低了40.4%和38.3%。研究表明细胞分裂蛋白DivIVA对细胞的形态和大小调控起重要作用;细胞分裂蛋白RodA和DivIB调控细胞分裂进程,进而影响细胞生长和溶剂合成进程。     

Ectopic expression of AINTEGUMENTA in Arabidopsis plants results in increased growth of floral organs.

AINTEGUMENTA (ANT) was previously shown to be involved in floral organ initiation and growth in Arabidopsis. ant flowers have fewer and smaller floral organs and possess ovules that lack integuments and a functional embryo sac. The present work shows that young floral meristems of ant plants are smaller than those in wild type. Failure to initiate the full number of organ primordia in ant flowers may result from insufficient numbers of meristematic cells. The decreased size of ant floral organs appears to be a consequence of decreased cell division within organ primordia. Ectopic expression of ANT under the control of the constitutive 35S promoter results in the development of larger floral organs. The number and shape of these organs is not altered and the size of vegetative organs is normal. Microscopic and molecular analyses indicate that the increased size of 35S::ANT sepals is the result of increased cell division, whereas the increased sizes of 35S::ANT petals, stamens, and carpels are primarily attributable to increased cell expansion. In addition, 35S::ANT ovules often exhibit increased growth of the nucellus and the funiculus. These results suggest that ANT stimulates cell growth in floral organs.     

Loss of growth homeostasis by genetic decoupling of cell division from biomass growth: implication for size control mechanisms

Growing cells adjust their division time with biomass accumulation to maintain growth homeostasis. Size control mechanisms, such as the size checkpoint, provide an inherent coupling of growth and division by gating certain cell cycle transitions based on cell size. We describe genetic manipulations that decouple cell division from cell size, leading to the loss of growth homeostasis, with cells becoming progressively smaller or progressively larger until arresting. This was achieved by modulating glucose influx independently of external glucose. Division rate followed glucose influx, while volume growth was largely defined by external glucose. Therefore, the coordination of size and division observed in wild‐type cells reflects tuning of two parallel processes, which is only refined by an inherent feedback‐dependent coupling. We present a class of size control models explaining the observed breakdowns of growth homeostasis.     

拟南芥叶绿体分裂突变体pdl37的基因鉴定与分析

pd137是经甲基磺酸乙脂（ethyl methane sulphonate, EMS）诱变并通过筛选得到的一个拟南芥叶绿体分裂突变体。该突变体的叶绿体表型与野生型相比有很大差异： 叶绿体面积显著增大, 细胞中叶绿体数量明显减少。遗传分析显示pd137的突变表型受隐性单基因控制。本研究通过遗传作图将该突变基因粗定位于拟南芥2号染色体的分子标记CH2-13.70和CH2-16.0区间内。该区间内已知的与叶绿体分裂相关的基因只有FtsZ2-1。对FtsZ2-1基因的测序结果显示pd137突变体的FtsZ2-1基因第505位碱基发生了无义突变, 使蛋白质翻译提前终止。该突变还严重影响了FtsZ2-1基因的mRNA水平。转基因互补实验进一步验证了该突变体表型是由于FtsZ2-1基因突变引起。本项工作为研究叶绿体分裂的机制提供了新材料和一些有用的线索。     

The effect of low temperature on patterns of cell division in developing second leaves of wild-type and slender mutant barley (Hordeum vulgare L.)

This study reports on investigations into the effect of long-term growth at reduced temperatures on cell elongation and cell division in the wild type and a temperature-insensitive ( slender ) mutant of barley. Plants were grown under two temperature regimes (20 and 5 °C) and the mitotic index, cell doubling time and cell lengths over the division and elongation zone were monitored at several stages of development in the second leaf. Leaf length and leaf growth rates were characteristically greater in the slender mutant than in the wild type and this was greatly exaggerated by growth at low temperature. Cell length and the length of the division zone were also greater in the slender mutant than in the wild type, and growing the plants at reduced temperature (5 °C) shortened cell lengths only in the wild type. The slender mutant had a higher mitotic index than the wild type, although in neither genotype was change in the mitotic index observed following growth at reduced temperature. Cell doubling time, on the other hand, was reduced by growth at reduced temperature in the wild type but not in the slender mutant. Thus, the data suggest very different growth responses to low temperature in the two genotypes. The results are discussed in terms of the ability of plants to sense their environment and optimize their metabolism for future growth.     

Mutations in the Diageotropica (Dgt) gene uncouple patterned cell division during lateral root initiation from proliferative cell division in the pericycle

In angiosperms, root branching requires a continuous re-initiation of new root meristems. Through some unknown mechanism, in most eudicots pericycle cells positioned against the protoxylem change identity and initiate patterned division, leading to formation of lateral root primordia that further develop into lateral roots. This process is auxin-regulated. We have observed that three mutations in the Diageotropica (Dgt) gene in tomato prevent primordium formation. Detailed analysis of one of these mutants, dgt1-1, demonstrated that the mutation does not abolish the proliferative capacity of the xylem-adjacent pericycle in the differentiated root portion. Files of shortened pericycle cells found in dgt1-1 roots were unrelated to primordium formation. Auxin application stimulated this unusual proliferation, leading to formation of a multi-layered xylem-adjacent pericycle, but did not rescue the primordium formation. In contrast to wild type, auxin could not induce any cell divisions in the pericycle of the most distal dgt1-1 root-tip portion. In wild-type roots, the Dgt gene promoter was expressed strongly in lateral root primordia starting from their initiation, and on auxin treatment was induced in the primary root meristem. Auxin level and distribution were altered in dgt1-1 root tissues, as judged by direct auxin measurements, and the tissue-specific expression of an auxin-response reporter was altered in transgenic plants. Together, our data demonstrate that the Dgt gene product, a type-A cyclophilin, is essential for morphogenesis of lateral root primordia, and that the dgt mutations uncouple patterned cell division in lateral root initiation from proliferative cell division in the pericycle.     

A role for leaf epidermis in the control of leaf size and the rate and extent of mesophyll cell division

Little is known about the control of leaf size in plants, yet there must be mechanisms by which organ size is measured. Because the control of leaf size extends beyond the action of individual genes or cells, an understanding of the role of leaf cell layers in the determination of leaf size is warranted. Following the construction of graft chimeras composed of small- and large-leaf genotypes of Nicotiana, bilateral leaf blade asymmetry was observed on leaves possessing either a genetically larger or smaller epidermis on one side of the midrib. Although cell size was unaffected by the genotype of the epidermis, the rate and extent of cell division in leaf epidermis altered the rate and extent of cell division in mesophyll and affected leaf size. The data presented neither prove nor disprove whether the mesophyll impacts epidermal cell division but provide the first unequivocal evidence that the extent of cell division in the leaf epidermis alters the extent of cell division in the mesophyll and is a factor regulating blade expansion and ultimate leaf size.     

Participation of the chemotactic system in regulating cell division in Escherichia coli

The possible role of the chemotaxis system in regulating cell division of Escherichia coli was studied. Attractants increased the rate of division whereas repellents reduced it. Non-metabolisable attractants analogues were also effective in stimulating cell division. Fucose, a non-metabolisable analogue of galactose, increased the rate of division by 20-25%. Co2+ at concentrations which had no effect on the tar-mutant division suppressed the division of the wild type. Likewise, indole at concentrations which did not influence the division of the tsr-mutant, suppressed the division of the wild type.     

烟草NtFtsZ2-1基因参与叶绿体分裂和扩大的调节

叶绿体虽然是植物细胞内一种极其重要的细胞器,但其分裂的分子机制尚不很清楚。已经证明FtsZ蛋白作为真核细胞分裂装置的一个关键成分,参与叶绿体的分裂过程。烟草的FtsZ基因属于2个不同的家族,在对NtFtsZ1家族成员研究的基础上,用正义和反义表达技术研究了NtFtsZ2家族成员NtFtsZ2-1基因在转基因烟草中的功能。显微分析结果表明NtFtsZ2-1基因的表达水平异常增强或减弱都会严重干扰叶绿体的正常分裂过程,导致叶绿体在形态和数目上的异常（体积明显增大,数目显著减少）,而单个叶肉细胞中叶绿体的总表面积在正反义转基因烟草和野生型烟草之间保持了相对稳定,没有发生明显的变化。同时还证明NtFtsZ2-1基因表达的变化对叶绿素含量和叶绿体的光合作用能力没有直接的影响。据此我们认为NtFtsZ2-1基因参与叶绿体的分裂和体积的扩大,其表达水平的波动会改变植物中叶绿体的数目和大小,而且在叶绿体的数目与体积之间可能存在一种补偿机制,保证叶绿体能最大限度地吸收光能,从而使光合作用得以正常进行。     

Development of surface pattern during division in Paramecium. II. Defective spatial control in the mutant kin241.

kin241 is a monogenic nuclear recessive mutation producing highly pleiotropic effects on cell size and shape, generation time, thermosensitivity, nuclear reorganization and cortical organization. We have analyzed the nature of the cortical disorders and their development during division, using various specific antibodies labelling either one of the cortical cytoskeleton components, as was previously done for analysis of cortical pattern formation in the wild type. Several abnormalities in basal body properties were consistently observed, although with a variable frequency: extra microtubules in either the triplets or in the lumen; nucleation of a second kinetodesmal fiber; abnormal orientation of the newly formed basal body with respect to the mother one. The latter effect seems to account for the major observed cortical disorders (reversal, intercalation of supplementary ciliary rows). The second major effect of the mutation concerns the spatiotemporal map of cortical reorganization during division. Excess basal body proliferation occurs and is correlated with modified boundaries of some of the cortical domains identified in the wild type on the basis of their basal body duplication pattern. This is the first mutant described in a ciliate in which both the structure and duplication of basal bodies and the body plan are affected. The data support the conclusion that the mutation does not alter the nature of the morphogenetic signal(s) which pervade the dividing cell, nor the competence of cytoskeletal structures to respond to signalling, but affects the local interpretation of the signals.     

Studies on the expression of a mutant with abnormal cell division in Chlamydomonas reinhardi

A mutant of Chlamydomonas reinhardi, in which cell and nuclear division are no longer synchronised, has been compared with wild type with the aim of clarifying the nature of the difference between the two strains. On entry into stationary phase, wild type cultures show a marked increase in protein, RNA and chlorophyll per cell, whereas mutant cultures do not show a comparable increase. The effect of chemicals which may interfere with particular aspects of the cell division process on the expression of the mutant have been studied. Vitamin B12 and the related compounds, benzimidazole, 5,6,dimethylbenzimidazole and cobaltous chloride increase the asynchrony between cell and nuclear division and consequently lead to the accumulation of large multinucleate cells. The mutant is less resistant than wild type to the inhibitory effects of caffeine.     

A Golgi-localized hexose transporter is involved in heterotrimeric G protein-mediated early development in Arabidopsis

Signal transduction involving heterotrimeric G proteins is universal among fungi, animals, and plants. In plants and fungi, the best understood function for the G protein complex is its modulation of cell proliferation and one of several important signals that are known to modulate the rate at which these cells proliferate is D-glucose. Arabidopsis thaliana seedlings lacking the beta subunit (AGB1) of the G protein complex have altered cell division in the hypocotyl and are D-glucose hypersensitive. With the aim to discover new elements in G protein signaling, we screened for gain-of-function suppressors of altered cell proliferation during early development in the agb1-2 mutant background. One agb1-2-dependent suppressor, designated sgb1-1(D) for suppressor of G protein beta1 (agb1-2), restored to wild type the altered cell division in the hypocotyl and sugar hypersensitivity of the agb1-2 mutant. Consistent with AGB1 localization, SGB1 is found at the highest steady-state level in tissues with active cell division, and this level increases in hypocotyls when grown on D-glucose and sucrose. SGB1 is shown here to be a Golgi-localized hexose transporter and acts genetically with AGB1 in early seedling development.     

T cell receptor-mediated signal transduction controlled by the beta chain transmembrane domain: apoptosis-deficient cells display unbalanced mitogen-activated protein kinases activities upon T cell receptor engagement.

The bases that support the versatility of the T cell receptor (TCR) to generate distinct T cell responses remain unclear. We have previously shown that mutant cells in the transmembrane domain of TCRbeta chain are impaired in TCR-induced apoptosis but are not affected in other functions. Here we describe the biochemical mechanisms by which this mutant receptor supports some T cell responses but fails to induce apoptosis. Extracellular signal-regulated protein kinase (ERK) is activated at higher and more sustained levels in TCRbeta-mutated than in wild type cells. Conversely, activation of both c-Jun N-terminal kinase and p38 mitogen-activated protein kinase is severely reduced in mutant cells. By attempting to link this unbalanced induction to altered upstream events, we found that ZAP-70 is normally activated. However, although SLP-76 phosphorylation is normally induced, TCR engagement of mutant cells results in lower tyrosine phosphorylation of LAT but in higher tyrosine phosphorylation of Vav than in wild type cells. The results suggest that an altered signaling cascade leading to an imbalance in mitogen-activated protein kinase activities is involved in the selective impairment of apoptosis in these mutant cells. Furthermore, they also provide new insights in the contribution of TCR to decipher the signals that mediate apoptosis distinctly from proliferation.     

EzrA contributes to the regulation of cell size in Staphylococcus aureus

EzrA is a negative regulator of FtsZ in Bacillus subtilis, involved in the coordination between cell growth and cell division and in the control of the cell elongation-division cycle. We have now studied the role of the Staphylococcus aureus homologue of the B. subtilis EzrA protein and shown that it is not essential for cell viability. EzrA conditional and null mutants have an overall increase of the average cell size, compared to wild type strains. In the larger ezrA mutant S. aureus cells, cell division protein FtsZ and the cell wall synthesizing Penicillin Binding Proteins (PBPs) are not properly localized. This suggests that there may be a maximum cell diameter that allows formation of a Z-ring capable of recruiting the other components of the divisome and of driving cytokinesis. We propose that the major role of EzrA in S. aureus is in cell size homeostasis.     

拟南芥叶绿体分裂突变体cpd111的基因定位与分析

通过EMS(ethyl methane sulphonate)诱变从拟南芥(Arabidopsis thaliana)突变体库中筛选到一个叶绿体分裂突变体(c)hloro(p)last (d)ivision 111 (cpd111).遗传学分析表明,该突变体的表型是单基因控制的隐性性状.与野生型相比,突变体植物细胞的叶绿体数量少,叶绿体形态和大小多样化,并且细胞体积与叶绿体数量之间无相关性.利用图位克隆的方法确定cpd111的突变基因为FtsZ1.进一步的分析表明,该突变影响FtsZ7基因mRNA的正常剪切和稳定性,使蛋白质翻译提前终止,最终导致叶绿体分裂异常.该工作为研究FtsZ1在叶绿体分裂中的作用提供了新的材料和线索.