Morphology, ontogeny and histochemistry of secretory trichomes of Geranium robertianum (Geraniaceae)

Geranium robertianum bears three types of glandular uniseriate trichomes which originate from a single protodermal cell and develop through periclinal divisions. Type I trichomes are procumbent and have an oval apical cell, two stalk cells and a basal cell. Type II trichomes are erect and have a pear shaped apical cell, two stalk cells and a basal cell. Type III trichomes are much longer than the other two types and have an elongated apical cell, five long stalk cells and a basal cell. Type I and type II trichomes are common on leaves while III trichomes are more abundant on flower structures.
Type I and type II trichomes secrete terpenoids and phenols. Type III trichomes are characterized by the accumulation of anthocyanins in the apical cell and secrete flavonoids.     

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.     

Autophagy functions in programmed cell death

Autophagic cell death is a prominent morphological form of cell death that occurs in diverse animals. Autophagosomes are abundant during autophagic cell death, yet the functional role of autophagy in cell death has been enigmatic. We find that autophagy and the Atg genes are required for autophagic cell death of Drosophila salivary glands. Although caspases are present in dying salivary glands, autophagy is required for complete cell degradation. Further, induction of high levels of autophagy results in caspase-independent autophagic cell death. Our results provide the first in vivo evidence that autophagy and the Atg genes are required for autophagic cell death and confirm that autophagic cell death is a physiological death program that occurs during development.     

细胞周期调控的研究进展

细胞周期是一种非常复杂和精细的调节过程,有大量调节蛋白参与其中。此过程的核心是细胞周期依赖性蛋白激酶（CDKs）。CDKs的激活又依赖于另一类呈细胞周期特异性或时相性表达的细胞周期蛋白（cyclins）,而CDKs调节的关键步骤是细胞周期检查点。PLKs是多种细胞周期检查点的主要调节因子,Aurora蛋白激酶主要在细胞有丝分裂期起作用。本文就上述因素在细胞周期进程中的作用作一综述。     

mig-5/Dsh controls cell fate determination and cell migration in C. elegans

Cell fate determination and cell migration are two essential events in the development of an organism. We identify mig-5, a Dishevelled family member, as a gene that regulates several cell fate decisions and cell migrations that are important during C. elegans embryonic and larval development. In offspring from mig-5 mutants, cell migrations are defective during hypodermal morphogenesis, QL neuroblast migration, and the gonad arm migration led by the distal tip cells (DTCs). In addition to abnormal migration, DTC fate is affected, resulting in either an absent or an extra DTC. The cell fates of the anchor cell in hermaphrodites and the linker cells in the male gonad are also defective, often resulting in the cells adopting the fates of their sister lineage. Moreover, 2 degrees vulval precursor cells occasionally adopt the 3 degrees vulval cell fate, resulting in a deformed vulva, and the P12 hypodermal precursor often differentiates into a second P11 cell. These defects demonstrate that MIG-5 is essential in determining proper cell fate and cell migration throughout C. elegans development.     

A hidden program in Drosophila peripheral neurogenesis revealed: fundamental principles underlying sensory organ diversity

How is cell fate diversity reliably achieved during development? Insect sensory organs have been a favorable model system for investigating this question for over 100 years. They are constructed using defined cell lineages that generate a maximum of cell diversity with a minimum number of cell divisions, and display tremendous variety in their morphologies, constituent cell types, and functions. An unexpected realization of the past 5 years is that very diverse sensory organs in Drosophila are produced by astonishingly similar cell lineages, and that their diversity can be largely attributed to only a small repertoire of developmental processes. These include changes in terminal cell differentiation, cell death, cell proliferation, cell recruitment, cell-cell interactions, and asymmetric segregation of cell fate determinants during mitosis. We propose that most Drosophila sensory organs are built from an archetypal lineage, and we speculate about how this stereotyped pattern of cell divisions may have been built during evolution.     

Alteration of cell cycle kinetics by reducing agents in human peripheral blood lymphocytes from adult and senescent donors

For improving cell proliferation reducing agents are routinely used as medium supplements in murine cell cultures, however, they are rarely used for human peripheral blood lymphocytes (PBLs). Data on changes in cell kinetics induced by reducing agents are not available. Here cell kinetic alterations induced by reducing agents in human lymphocytes are revealed by applying flow cytometric BrdUrd/Hoechst cell cycle analysis and by using the exit kinetic model of Smith and Martin. Applying alpha-thioglycerol (a-TG) as a model compound it was shown that the major cell kinetic effect is a shortening of the mean duration of the G0/G1 phase. The minimum G0/G1 phase duration and the percentage of the non-cycling G0/G1 cell fraction decrease only slightly. Moreover, a lower number of PBL's are arrested in the G2/M phase of the 1st cell cycle. The durations of the S and G2/M phase in the 1st and G1 phase in the 2nd cycle are not affected. These cell kinetic effects are identical for lymphocytes from both adult and senescent donors. The supplementation of the cell cultures with recombinant IL-2 did not induce similar cell kinetic alterations compared with a-TG. This indicates that the variation of the cell cycle progression factor IL-2 is not solely responsible for improvement of the cell activation process in the G0/G1 phase.     

The gapped xylem mutant identifies a common regulatory step in secondary cell wall deposition

The phenotype of the novel gapped xylem (gpx) mutant is described. gpx plants exhibit gaps in the xylem in positions where xylem elements would normally be located. These gaps are not part of the transpiration stream and result in gpx plants having fewer functional xylem elements. The gaps are due to the absence of a secondary cell wall in developing xylem elements, resulting in complete degradation of these elements during cell death, and illustrate the importance of the secondary cell wall in retaining a functional xylem element following programmed cell death. Consequently the gpx phenotype suggests that the processes of secondary cell wall formation and cell death are independently regulated in developing xylem. gpx plants also exhibit a highly irregular pattern of secondary cell wall thickening in interfascicular cells, with some cells apparently undergoing little or no secondary cell wall deposition. Secondary cell wall deposition in plants involves the co-ordinate regulation of several complex metabolic pathways. The gpx mutant identifies a key step involved in regulating the deposition of secondary cell wall material in both xylem and interfascicular cells, and suggests that a common regulatory step controls secondary cell wall formation in these diverse cell types. The gpx mutant offers a unique opportunity to elucidate the mechanism by which the complex processes involved in secondary cell wall formation are co-ordinately regulated.     

Autophagy functions in programmed cell death

Autophagic cell death is a prominent morphological form of cell death that occurs in diverse animals. Autophagosomes are abundant during autophagic cell death, yet the functional role of autophagy in cell death has been enigmatic. We find that autophagy and the Atg genes are required for autophagic cell death of Drosophila salivary glands. Although caspases are present in dying salivary glands, autophagy is required for complete cell degradation. Further, induction of high levels of autophagy results in caspase-independent autophagic cell death. Our results provide the first in vivo evidence that autophagy and the Atg genes are required for autophagic cell death and confirm that autophagic cell death is a physiological death program that occurs during development.

Addendum to: Berry DL, Baehrecke EH. Growth arrest and autophagy are required for programmed salivary gland cell degradation in Drosophila. Cell 2007; 131:1137-48.     

Correlating cell behavior with tissue topology in embryonic epithelia

Measurements on embryonic epithelial tissues in a diverse range of organisms have shown that the statistics of cell neighbor numbers are universal in tissues where cell proliferation is the primary cell activity. Highly simplified non-spatial models of proliferation are claimed to accurately reproduce these statistics. Using a systematic critical analysis, we show that non-spatial models are not capable of robustly describing the universal statistics observed in proliferating epithelia, indicating strong spatial correlations between cells. Furthermore we show that spatial simulations using the Subcellular Element Model are able to robustly reproduce the universal histogram. In addition these simulations are able to unify ostensibly divergent experimental data in the literature. We also analyze cell neighbor statistics in early stages of chick embryo development in which cell behaviors other than proliferation are important. We find from experimental observation that cell neighbor statistics in the primitive streak region, where cell motility and ingression are also important, show a much broader distribution. A non-spatial Markov process model provides excellent agreement with this broader histogram indicating that cells in the primitive streak may have significantly weaker spatial correlations. These findings show that cell neighbor statistics provide a potentially useful signature of collective cell behavior.     

A computational approach for inferring the cell wall properties that govern guard cell dynamics

Guard cells dynamically adjust their shape in order to regulate photosynthetic gas exchange, respiration rates and defend against pathogen entry. Cell shape changes are determined by the interplay of cell wall material properties and turgor pressure. To investigate this relationship between turgor pressure, cell wall properties and cell shape, we focused on kidney‐shaped stomata and developed a biomechanical model of a guard cell pair. Treating the cell wall as a composite of the pectin‐rich cell wall matrix embedded with cellulose microfibrils, we show that strong, circumferentially oriented fibres are critical for opening. We find that the opening dynamics are dictated by the mechanical stress response of the cell wall matrix, and as the turgor rises, the pectinaceous matrix stiffens. We validate these predictions with stomatal opening experiments in selected Arabidopsis cell wall mutants. Thus, using a computational framework that combines a 3D biomechanical model with parameter optimization, we demonstrate how to exploit subtle shape changes to infer cell wall material properties. Our findings reveal that proper stomatal dynamics are built on two key properties of the cell wall, namely anisotropy in the form of hoop reinforcement and strain stiffening.     

An immunocytochemical and electron-microscopical study of endocrine cells in the gut and pancreas of a stomachless teleost fish,Barbus conchonius (Cyprinidae)

Summary Four immunoreactive endocrine cell types can be distinguished in the pancreatic islets of B. conchonius: insulin-producing B cells, somatostatin-producing A₁ (= D) cells, glucagon-producing A₂ cells and pancreatic poly-peptide-producing PP cells. The principal islet of this species contains only a few PP cells, while many PP cells are present in the smaller islets. Except for the B cell all pancreatic endocrine cell types are also present in the pancreatic duct.At least six enteroendocrine cell types are present in the gut of B. conchonius: 1. a cell type (I) with small secretory granules, present throughout the intestine, and possibly involved in the regulation of gut motility; 2. a C-terminal gastrin immunoreactive cell, probably producing a caerulein-like peptide; these cells are located at the upper parts of the folds, especially in the proximal part of the intestinal bulb; 3. a met-enkephalin-immunoreactive cell, present throughout the first segment; 4. a glucagon-immunoreactive cell, which is rare in the first segment; 5. a PP-immunoreactive cell, mainly present in the first half of the first segment; 6. an immunoreactive cell, which cannot at present be specified, located in the intestinal bulb. The latter four cell types are mostly located in the basal parts of the folds, although some PP-immunoreactive cells can also be found in the upper parts.Most if not all enteroendocrine cells are of the open type. The possible functions of all enteroendocrine cell types are discussed.Abbreviations BPP bovine pancreatic polypeptide - CCK cholecystokinin - GEP gastro-entero-pancreatic - GIP gastric inhibitory peptide or glucose-dependent insulin releasing peptide - PPP pig pancreatic polypeptide - VIP vasoactive intestinal polypeptide     

Generation and Fates of Supernumerary Centrioles in Dividing Cells

The centrosome is a subcellular organelle from which a cilium assembles. Since centrosomes function as spindle poles during mitosis, they have to be present as a pair in a cell. How the correct number of centrosomes is maintained in a cell has been a major issue in the fields of cell cycle and cancer biology. Centrioles, the core of centrosomes, assemble and segregate in close connection to the cell cycle. Abnormalities in centriole numbers are attributed to decoupling from cell cycle regulation. Interestingly, supernumerary centrioles are commonly observed in cancer cells. In this review, we discuss how supernumerary centrioles are generated in diverse cellular conditions. We also discuss how the cells cope with supernumerary centrioles during the cell cycle.     

Rapid detection of low‐level HeLa cell contamination in cell culture using nested PCR

HeLa cells are a commonly used cell line in many biological research areas. They are not picky for culture medium and proliferate rapidly. HeLa cells are a notorious source of cell cross‐contamination and have been found to be able to contaminate a wide range of cell lines in cell culture. In this study, we reported a simple and efficient method for detecting the presence of HeLa cell contamination in cell culture. HPV‐18 was used as a biomarker. The cell culture supernatant was used directly as the template for nested PCR without extracting nucleic acid. By PCR amplification of the cell culture supernatant with the designed primers, we were able to detect the presence of HeLa cells in the culture. The sensitivity of this method can reach 1%, which is 10‐fold higher than Short tandem repeat sequence (STR) profiling. This simple, rapid, and “noninvasive” quality checking method should find applications in routine cell culture practice.     

Repetitive cellular patterns in the secondary phloem of conifer and dicot trees,and a hypothesis for their development

Abstract

The radial fusiform cell files of the secondary phloem of conifers and dicots are composed of different cell types?–?fibres, parenchyma and sieve cells (in conifers), or sieve elements plus companion cells (in dicots). These cell types are arranged in characteristic, species-specific sequences along the radii of the files. The sequences are replicated in adjacent files and this leads to tangential bands of similar cell type. Moreover, the sequences are developed repetitively so that a sequence found in one year's growth increment of phloem is repeated in the next increment. In some species, many repetitions of the same sequence occur within one annual increment. A general hypothesis has been developed to account for the radial sequences of cell types. It is proposed that there is a gradient of a phloem-promoting morphogen, a series of morphogen thresholds for the determination of each phloem cell type, and a particular spatio-temporal pattern of periclinal cell division in the phloem domain of the vascular cambium that generates a corresponding pattern of cell displacement through the morphogen gradient in the immediately post-mitotic zone of cell determination. The feasibility of the hypothesis was supported by means of simulation which, using a constant set of initial conditions, could reproduce very nearly all the radial sequences of cell types found in the secondary phloem of a range of species of conifers and woody dicots. The tangential banding of the various cell types suggests that cell production and cell determination are events which occur synchronously across the radial files. The repeating blocks of cell types may constitute functional modules of phloem tissue, and the constituent cells probably have particular patterns of symplasmic connections and mechano-structural properties.     

Studying cell biology in the skin

Advances in cell biology have often been driven by studies in diverse organisms and cell types. Although there are technical reasons for why different cell types are used, there are also important physiological reasons. For example, ultrastructural studies of vesicle transport were aided by the use of professional secretory cell types. The use of tissues/primary cells has the advantage not only of using cells that are adapted to the use of certain cell biological machinery, but also of highlighting the physiological roles of this machinery. Here we discuss advantages of the skin as a model system. We discuss both advances in cell biology that used the skin as a driving force and future prospects for use of the skin to understand basic cell biology. A unique combination of characteristics and tools makes the skin a useful in vivo model system for many cell biologists.     

Asymmetric cell divisions in flowering plants - one mother, "two-many" daughters

Plant development shows a fascinating range of asymmetric cell divisions. Over the years, however, cellular differentiation has been interpreted mostly in terms of a mother cell dividing mitotically to produce two daughter cells of different fates. This popular view has masked the significance of an entirely different cell fate specification pathway, where the mother cell first becomes a coenocyte and then cellularizes to simultaneously produce more than two specialized daughter cells. The "one mother - two different daughters" pathways rely on spindle-assisted mechanisms, such as translocation of the nucleus/spindle to a specific cellular site and orientation of the spindle, which are coordinated with cell-specific allocation of cell fate determinants and cytokinesis. By contrast, during "coenocyte-cellularization" pathways, the spindle-assisted mechanisms are irrelevant since cell fate specification emerges only after the nuclear divisions are complete, and the number of specialized daughter cells produced depends on the developmental context. The key events, such as the formation of a coenocyte and migration of the nuclei to specific cellular locations, are coordinated with cellularization by unique types of cell wall formation. Both one mother - two different daughters and the coenocyte-cellularization pathways are used by higher plants in precise spatial and time windows during development. In both the pathways, epigenetic regulation of gene expression is crucial not only for cell fate specification but also for its maintenance through cell lineage. In this review, the focus is on the coenocyte-cellularization pathways in the context of our current understanding of the asymmetric cell divisions. Instances where cell differentiation does not involve an asymmetric division are also discussed to provide a comprehensive account of cell differentiation.     

Analysis of cell growth and diffusion in a scaffold for cartilage tissue engineering

Developments in tissue engineering over the past decade have offered promising future for the repair and reconstruction of damaged tissues. To regenerate three dimensional and weight-bearing implants, advances in biomaterials and manufacturing technologies prompted cell cultivations with natural or artificial scaffolds, in which cells are allowed to proliferate, migrate, and differentiate in vitro. In this article, we develop a mathematical model for cell growth in a porous scaffold. By treating the cell-scaffold construct as a porous medium, a continuum model is set up based on basic principles of mass conservation. In addition to cell growth kinetics, we incorporate cell diffusion in the model to describe the effects of cell random walks. Computational results are compared to experimental data found in the literature. With this model, we are able to investigate cell motility, heterogeneous cell distributions, and non-uniform seeding for tissue engineering applications. Results show that random walks tend to enhance uniform cell spreads in space, which in turn increases the probabilities for cells to acquire nutrients; therefore random walks are likely to be a positive contribution to the overall cell growth on scaffolds.     

Trans-Golgi Network—An Intersection of Trafficking Cell Wall Components

The cell wall, a crucial cell compartment, is composed of a network of polysaccharides and proteins, providing structural support and protection from external stimuli. While the cell wall structure and biosynthesis have been extensively studied, very little is known about the transport of polysaccharides and other components into the developing cell wall. This review focuses on endomembrane trafficking pathways involved in cell wall deposition. Cellulose synthase complexes are assembled in the Golgi, and are transported in vesicles to the plasma membrane. Non-cellulosic polysaccharides are synthesized in the Golgi apparatus, whereas cellulose is produced by enzyme complexes at the plasma membrane. Polysaccharides and enzymes that are involved in cell wall modification and assembly are transported by distinct vesicle types to their destinations; however, the precise mechanisms involved in selection, sorting and delivery remain to be identified. The endomembrane system orchestrates the delivery of Golgi-derived and possibly endocytic vesicles carrying cell wall and cell membrane components to the newly-formed cell plate. However, the nature of these vesicles, their membrane compositions, and the timing of their delivery are largely unknown. Emerging technologies such as chemical genomics and proteomics are promising avenues to gain insight into the trafficking of cell wall components.