A genome-wide resource of cell cycle and cell shape genes of fission yeast

To identify near complete sets of genes required for the cell cycle and cell shape, we have visually screened a genome-wide gene deletion library of 4843 fission yeast deletion mutants (95.7% of total protein encoding genes) for their effects on these processes. A total of 513 genes have been identified as being required for cell cycle progression, 276 of which have not been previously described as cell cycle genes. Deletions of a further 333 genes lead to specific alterations in cell shape and another 524 genes result in generally misshapen cells. Here, we provide the first eukaryotic resource of gene deletions, which describes a near genome-wide set of genes required for the cell cycle and cell shape.     

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.     

Glycoproteins and lectins in cell adhesion and cell recognition processes

Summary The discovery of endogenous lectins having specific and high affinity for the carbohydrate portions of glycoproteins has opened up new directions in the field of cell adhesion and cell recognition. Two endogenous lectins, termed as CSL and R1, initially isolated from the rat cerebellum and having a wide distribution in mammalian tissues, have been shown to participate in essential mechanisms of cell adhesion. The membrane-bound lectin R1 seems to be involved in transient recognition between neuronal cells, followed by elimination of the glycoprotein ligands at the surface of the recognized cell. In contrast, CSL is a molecule involved in adhesion between various normal or transformed cells since it participates in the formation of tight junctions. The glycoprotein ligands recognized with higher affinity by these two lectins seem to possess a special structure which defines a sub-class of oncofetal HNK-1 glycans. The over-expression of the glycoprotein ligands of these lectins in most transformed cells provides new tools for understanding the underlying mechanism of malignant transformation as well as the generation of signals through cell adhesion.     

Cell wars: regulation of cell survival and proliferation by cell competition

During cell competition fitter cells take over the tissue at the expense of viable, but less fit, cells, which are eliminated by induction of apoptosis or senescence. This probably acts as a quality-control mechanism to eliminate suboptimal cells and safeguard organ function. Several experimental conditions have been shown to trigger cell competition, including differential levels in ribosomal activity or in signalling pathway activation between cells, although it is unclear how those differences are sensed and translated into fitness levels. Many of the pathways implicated in cell competition have been previously linked with cancer, and this has led to the hypothesis that cell competition could play a role in tumour formation. Cell competition could be co-opted by cancer cells to kill surrounding normal cells and boost their own tissue colonization. However, in some cases, cell competition could have a tumour suppressor role, as cells harbouring mutations in a subset of tumour suppressor genes are killed by wild-type cells. Originally described in developing epithelia, competitive interactions have also been observed in some stem cell niches, where they play a role in regulating stem cell selection, maintenance and tissue repopulation. Thus competitive interactions could be relevant to the maintenance of tissue fitness and have a protective role against aging.     

Dlg,Scribble and Lgl in cell polarity,cell proliferation and cancer

Dlg (Discs large), Scrib (Scribble) and Lgl (Lethal giant larvae) are evolutionarily conserved components of a common genetic pathway that link the seemingly disparate functions of cell polarity and cell proliferation in epithelial cells. dlg, scrib and lgl have been identified as tumour suppressor genes in Drosophila, mutations of which cause similar phenotypes, involving disruption of cell polarity and neoplastic overgrowth of tissues. The molecular mechanisms by which Dlg, Scrib and Lgl proteins regulate cell proliferation are not clear, but there is some evidence that epithelial polarisation is required for this regulation. Dlg, Scrib and Lgl are highly conserved between human and Drosophila, and we discuss evidence that these proteins also play a role in cancer progression in humans.     

Inheritance of malignancy in somatic cell hybrids

After a recall of the importance of early basic developments of in vitro established cell lines for investigations on malignant transformation, a survey of essential steps in the study of malignancy by means of somatic cell hybridization is presented. Since the early sixties, in vitro crosses of malignant versus nonmalignant parental cells have provided many experimental models in which mechanisms of expression of malignancy have been approached. Allogenic as well as xenogenic cell matings resulted in tumor-producing or nontumorigenic hybrids which have been analyzed, particularly in terms of karyology in order to determine possible chromosomal patterns linked with inheritance of malignancy and its suppression. The authors discuss the successive concepts devised for interpretation of experimental data, implicating specific genetic "normalizing" information, genetic dosage as well as, more recently, epigenetic and cytoplasmic mechanisms.     

Interspecific cell markers and cell lineage in birds

A cell marking technique based on the structural differences existing between the interphase nucleus in two closely related species of birds, the chick and the Japanese quail, is described. In all embryonic and adult cell types of the quail, a large mass of heterochromatin is associated with the nucleolus making quail and chick cells easy to identify at the single cell level after application of any DNA-specific staining procedure and also at the electron microscope level. This method has been largely used to construct chimeras in ovo and to study dynamic processes such as cell migrations or cell lineage segregation during ontogeny. Recently monoclonal antibodies specific for either quail or chick antigenic determinants (for example, class II MHC antigens) have been prepared, increasing the interest of the quail-chick chimera system as an experimental model.     

Molecular basis of cell integrity and morphogenesis in Saccharomyces cerevisiae.

In fungi and many other organisms, a thick outer cell wall is responsible for determining the shape of the cell and for maintaining its integrity. The budding yeast Saccharomyces cerevisiae has been a useful model organism for the study of cell wall synthesis, and over the past few decades, many aspects of the composition, structure, and enzymology of the cell wall have been elucidated. The cell wall of budding yeasts is a complex and dynamic structure; its arrangement alters as the cell grows, and its composition changes in response to different environmental conditions and at different times during the yeast life cycle. In the past few years, we have witnessed a profilic genetic and molecular characterization of some key aspects of cell wall polymer synthesis and hydrolysis in the budding yeast. Furthermore, this organism has been the target of numerous recent studies on the topic of morphogenesis, which have had an enormous impact on our understanding of the intracellular events that participate in directed cell wall synthesis. A number of components that direct polarized secretion, including those involved in assembly and organization of the actin cytoskeleton, secretory pathways, and a series of novel signal transduction systems and regulatory components have been identified. Analysis of these different components has suggested pathways by which polarized secretion is directed and controlled. Our aim is to offer an overall view of the current understanding of cell wall dynamics and of the complex network that controls polarized growth at particular stages of the budding yeast cell cycle and life cycle.     

Pom1 and cell size homeostasis in fission yeast

Cells sense their size and use this information to coordinate cell division with cell growth to maintain a constant cell size within a given population. A model has been proposed for cell size control in the rod-shaped cells of the fission yeast, Schizosaccharomyces pombe. This involves a protein localized to the cell ends, which inhibits mitotic activators in the middle of the cell in a cell size-dependent manner. This protein, Pom1, along with another tip-localized protein, Nif1, have been implicated as direct sensors of cell size controlling the onset of mitosis. Here we have investigated cell size variability and size homeostasis at the G₂/M transition, focusing on the role of pom1 and nif1. Cells deleted for either of these 2 genes show wild-type size homeostasis both in size variability analyses and size homeostasis experiments. This indicates that these genes do not have a critical role as direct cell size sensors in the control mechanism. Cell size homeostasis also seems to be independent of Cdc2–Tyr15 phosphorylation, suggesting that the size sensing mechanism in fission yeast may act through an unidentified pathway regulating CDK activity by an unknown mechanism.     

植物原生质体在分子细胞生物学研究中的应用

植物原生质体是去除了细胞壁的裸露细胞,其具有细胞全能性,现广泛应用于植物分子细胞生物学的研究中,可以大大缩减实验周期,并有助于得到体内实验的实时检测数据。该文除了介绍植物原生质体的提取和纯化方法外,还对国内外利用各种植物的原生质体进行细胞瞬时转化、亚细胞定位、细胞融合和大分子复合物相互作用等试验进行了总结和讨论。植物原生质体还可用于基因表达模式的实时检测,并作为生物反应器的受体细胞进行代谢物的体外生产。此外,还对当前该技术所面临的瓶颈进行了分析,为植物原生质体在分子细胞生物学领域的应用提供帮助,为技术的优化和推广提供参考。     

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.     

Non-hormonal cell types in the pituitary candidating for stem cell

Hormone balances in the body are primarily governed by the hypothalamus-pituitary system. For its pivotal role, the pituitary gland relies on an assortment of different hormone-producing cell types, the proportions of which dynamically change in response to fluctuating endocrine demands. Mechanisms of pituitary cellular plasticity are at present far from understood, and may include proliferation and transdifferentiation of hormonal cells. Whether new cells also originate by recruitment from stem cells is unsettled, although this idea has frequently been proposed. Here, I will review these data by focusing on the non-hormonal cell types that have been advanced as candidates for the pituitary stem cell position.     

Asymmetric cell division and cell fate in plants

A variety of approaches has recently been employed to investigate how sister cells adopt distinct fates following asymmetric divisions during plant development. Surgical and drug studies have been used to analyze asymmetric divisions during both early embryogenesis in brown algae and pollen development in tobacco. Genetic screens have been used to identify genes in Arabidopsis thaliana that are required for specific asymmetric cell divisions during pollen and root development. These studies indicate that cell polarity and division orientation are closely tied to the process of cell fate specification, and suggest that differential inheritance of determinants and positional information may both be involved in the specification of cell fates following asymmetric cell division.     

Requirement for Arf6 in cell adhesion, migration, and cancer cell invasion

Cell movements are essential to life, in a variety of aspects including development, repair and defence processes. Cell migration is a multifactorial process in which a number of distinct events occur simultaneously. Besides its strong appeal towards the basic sciences, the molecular mechanisms of cell migration have long been major targets of oncology, including clinical studies aiming for cancer therapy and prevention. For the further advancement of these studies, as well as for the benefit of its clinical applications, it is important to understand the fundamental machinery and mechanisms regulating cell adhesion and motility. Here the possible roles of a small GTP-binding protein, Arf6, in epithelial cell adhesion and migration, and also in cancer cell invasion, are discussed.     

昆虫细胞系的培养和建立技术

迄今已经报道的昆虫细胞系有800株以上。昆虫细胞系在昆虫病理学、寄生虫学、内分泌学、遗传学和分子生物学等基础和应用研究中得到越来越广泛的应用。本文结合我们研究的结果和实践经验,概括了国内外昆虫细胞系建立技术的研究进展,包括昆虫细胞培养的发展、昆虫细胞系建立技术、不同昆虫组织来源细胞系的建立方法和过程,以及对昆虫细胞系特征的鉴定等方面。     

Emerging key role of cell cycle regulators in cell metabolism

The role of cell cycle regulators in the control of cell proliferation has been extensively studied, but independently of these functions in cell proliferation, it now appears that these proteins are also key to the adapted metabolic response of the cells. This has some logic since cell cycle is linked to metabolic control. This review focusses on the involvment of cyclins, cyclin dependent kinases or E2F factor in the control of adipogenesis, glucidic homeostasis, and energy consumption. Murine models in which genes encoding these regulators have been invalidated have been key to unravel these novel functions of cell cycle regulators in cell metabolism. Furthermore, these findings may also have some relevance for metabolic disorders such as obesity or diabetes.     

Penicillin binding proteins: key players in bacterial cell cycle and drug resistance processes

Bacterial cell division and daughter cell formation are complex mechanisms whose details are orchestrated by at least a dozen different proteins. Penicillin-binding proteins (PBPs), membrane-associated macromolecules which play key roles in the cell wall synthesis process, have been exploited for over 70 years as the targets of the highly successful beta-lactam antibiotics. The increasing incidence of beta-lactam resistant microorganisms, coupled to progress made in genomics, genetics and immunofluorescence microscopy techniques, have encouraged the intensive study of PBPs from a variety of bacterial species. In addition, the recent publication of high-resolution structures of PBPs from pathogenic organisms have shed light on the complex intertwining of drug resistance and cell division processes. In this review, we discuss structural, functional and biological features of such enzymes which, albeit having initially been identified several decades ago, are now being aggressively pursued as highly attractive targets for the development of novel antibiotherapies.     

Development of new cell lines for animal cell biotechnology

Mammalian cell culture has been an important technique in laboratory-scale experimentation for many decades. Developments in large-scale culture have been due to the need to grow large numbers of cells to support the growth of viruses for vaccine production, and more recently, for growing hybridoma cells as a source of monoclonal antibody. Increasingly, however, pharmaceutical products such as hormones, enzymes, growth factors, and clotting factors are being produced from cell lines which have been manipulated by recombinant DNA techniques. It is clear, therefore, that the high cost of growing mammalian cells on a large scale does not necessarily prohibit their use for biotechnology, and indeed there is considerable evidence to suggest that animal cell biotechnology will continue to be a major growth area in the future.     

Totipotency and embryogenesis in plant cell and tissue cultures

Summary An important development in the field of plant cell and tissue culture has been the demonstration in the past decade of the totipotency of higher plant cells. Isolated single cells were first successfully grown on a nurse tissue separated by a filter paper and gave rise to a callus tissue. Later, completely isolated single cells of tobacco were grown in microchambers to form small clumps of cells which then could be differentiated to form adult tobacco plants. Indirect evidence of the totipotency of higher plant cells has also been provided in a number of other plants. Embryo-like structures (or embryoids) or whole plants, or both, have been obtained from such highly differentiated cells as the pollen grains (gametic and haploid), photosynthetic palisade cells in leaves, epidermal cells from the hypocytyl, and the triploid endosperm cells; all of these cell types perform very highly specialized functions in the plant. Plant protoplasts (cell wall is digested with enzymes) have also been cultured to give rise to normal adult plants. In many instances embryoids have been produced in vitro from several species of flowering plants which do not show such asexual activity in nature. These embryoids are normally indistinguishable morphologically from embryos produced by gametic fusion, often follow the same pattern of cell divisions and differentiation as the developing zygote, and are economically important as they provide clonal populations. Early work in this area emphasized the necessity of dissociating tissues into single cells and providing a nutritional environment identical to that of the zygote in the embryo sac (usually by supplementing the medium with liquid endosperm from coconuts), before the cells could be released morphogenetically to express their totipotency by forming embryoids. Much of the recent work, however, has shown that perfect development of embryoids can be obtained in completely synthetic media in callus tissues as well as in suspension cultures. This paper is dedicated to the memory of the late Professor Philip R. White, a dear friend who provided much counsel and inspiration to us both. for his pioneering work, valuable contributions and untiring efforts in developing the science of plant cell, tissue, and organ culture. Florida Agricultural Experiment Stations Journal Series No. 4699. Presented in the Symposium on Functional Differentiated Systems at the 23rd Annual Meeting of the Tissue Culture Association, Los Angeles, California, June 5–8, 1972.