Cell Life Cycle Research Articles

X-ray Absorption Spectroscopy Characterization of a Li/S Cell.

The X-ray absorption spectroscopy technique has been applied to study different stages of the lithium/sulfur (Li/S) cell life cycle. We have investigated how speciation of S in Li/S cathodes changes upon the introduction of CTAB (cetyltrimethylammonium bromide, CH3(CH2)15N+(CH3)3Br−) and with charge/discharge cycling. The introduction of CTAB changes the synthesis reaction pathway dramatically due to the interaction of CTAB with the terminal S atoms of the polysulfide ions in the Na2Sx solution. For the cycled Li/S cell, the loss of electrochemically active sulfur and the accumulation of a compact blocking insulating layer of unexpected sulfur reaction products on the cathode surface during the charge/discharge processes make the capacity decay. A modified coin cell and a vacuum-compatible three-electrode electro-chemical cell have been introduced for further in-situ/in-operando studies.

Cell cycle inhibitors in oral leukoplakia: A review

Cell cycle is a complex and coordinated process characterized by orderly progression in the life cycle of cells mainly orchestrated by cyclins and cyclin dependent kinases (CDK) and their inhibitors. The kinases drive the cell cycle by phosphorylating critical target proteins that are required for progression of cell to the next phase of cell cycle. This progress is tightly regulated by a group of cell cycle inhibitors known as CDK inhibitors which may be responsible for maintenance of cell cycle and proliferation arrest once the cells’ developmental fate has been reached. Cell cycle inhibitors may act as checkpoints to identify the defective components of the cell thereby aiding in its repair and hence inactivation of these genes may interfere with the terminal differentiation thus leading to unrestricted proliferation and tumorigenesis. Cell proliferation is an important property of malignant tumor cells and dysregulation of genes governing the cell cycle is of considerable significance in the development of oral squamous cell carcinoma. Most OSCC generally develop by the malignant transformation of potentially malignant disorders the most common of which is leukoplakia. Hence evaluation of these genetic alterations in leukoplakia can be useful in assessment of the potential for malignant transformation and may also aid in attempting any therapeutic strategies at this stage. This review aims to provide data related to the role of cell cycle inhibitors in oral leukoplakia highlighting their role in malignant transformation.

Functional characterization of Bombyx mori nucleopolyhedrovirus mutant lacking late expression factor 9.

Baculoviridae is a family of invertebrate viruses with large double-stranded DNA genomes. Proteins encoded by some late expression factor (lef ) genes are involved in the regulation of viral gene expression. Lef-9 is one of four transcription-specific Lefs, which are components of the virus-encoded RNA polymerase, and can initiate and transcribe late and very late genes. As a multifunctional protein encoded by the Bombyx mori nucleopolyhedrovirus (BmNPV), Lef-9 may be involved in the regulation of viral propagation. However, the underlying mechanism remains unclear. To determine the role of lef-9 in baculovirus infection, lef-9-knockout virus (lef-9-KO-Bacmid virus) was constructed using the Red recombination system, and the Bac-to-Bac system was used to prepare lef-9-repaired virus (lef-9-Re-Bacmid virus). The lef-9-KO virus did not produce infectious viruses or show infection activity, while the lef-9-repaired virus recovered both. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis of the transcription levels in wild-type-Bacmid, lef-9-KO-Bacmid, and lef-9-Re-Bacmid viruses showed that the lef-9-KO bacmid had little effect on viral genome replication. However, the transcription levels of the early and late viral genes, lef-3, ie-1, vp39, and p10, were significantly lower in BmN cells transfected with lef-9-KO-Bacmids than in the controls. Electron microscopy showed no visible enveloped virions in cells transfected with lef-9-KO-Bacmids, while many mature virions in cells transfected with lef-9-Re-Bacmid and wt-Bacmid were present. Thus, lef-9 was not essential for viral genome replication, but significantly affected viral gene transcription and expression in all periods of cell life cycle.

Optimal Strategies for Virus Propagation

This paper explores a number of questions regarding optimal strategies evolved by viruses upon entry into a vertebrate host. The infected cell life cycle consists of a non-productively infected stage in which it is producing virions but not releasing them and of a productively infected stage in which it is just releasing virions. The study explores why the infected cell cycle should be so delineated, something which is akin to a classic “bang-bang control” or all-or-none principle. The times spent in each of these stages represent a viral strategy to optimize peak viral load. Increasing the time spent in the non-productively infected phase (τ1) would lead to a concomitant increase in peak viremia. However increasing this time would also invite a more vigorous response from Cytotoxic TLymphocytes (CTLs). Simultaneously, if there is a vigorous antibody response, then we might expect τ1 to be high, in order that the virus builds up its population and conversely if there is a weak antibody response, τ1 might be small. These tradeoffs are explored using a mathematical model of virus propagation using Ordinary Differential Equations (ODEs). The study raises questions about whether common viruses have actually settled into an optimum, the role for reliability and whether experimental infections of hosts with non-endemic strains could help elicit answers about viral progression.

Nucleus pulposus phenotypic markers to determine stem cell differentiation: fact or fiction?

Progress in mesenchymal stem cell (MSC) based therapies for nucleus pulposus (NP) regeneration are hampered by a lack of understanding and consensus of the normal NP cell phenotype. Despite the recent consensus paper on NP markers, there is still a need to further validate proposed markers. This study aimed to determine whether an NP phenotypic profile could be identified within a large population of mature NP samples.qRT-PCR was conducted to assess mRNA expression of 13 genes within human non-degenerate articular chondrocytes (AC) (n=10) and NP cells extracted from patients across a spectrum of histological degeneration grades (n=71). qRT-PCR results were used to select NP marker candidates for protein expression analysis.Differential expression at mRNA between AC and non-degenerate NP cells was only observed for Paired Box Protein 1 (PAX1) and Forkhead box F1 (FOXF1). In contrast no other previously suggested markers displayed differential expression between non-degenerate NP and AC at mRNA level. PAX1 and FOXF1 protein expression was significantly higher in the NP compared to annulus fibrosus (AF), cartilaginous endplate (CEP) and AC. In contrast Laminin-5 (LAM-332), Keratin-19 (KRT-19) and Hypoxia Inducible Factor 1 alpha (HIF1α) showed no differential expression in NP cells compared with AC cells.A marker which exclusively differentiates NP cells from AF and AC cells remains to be identified, raising the question: is the NP a heterogeneous population of cells? Or does the natural biological variation during IVD development, degeneration state and even the life cycle of cells make finding one definitive marker impossible?

Rho GTPases in ameloblast differentiation.

SummaryDuring tooth development, ameloblasts differentiate from inner enamel epithelial cells to enamel-forming cells by modulating the signal pathways mediating epithelial–mesenchymal interaction and a cell-autonomous gene network. The differentiation process of epithelial cells is characterized by marked changes in their morphology and polarity, accompanied by dynamic cytoskeletal reorganization and changes in cell–cell and cell–matrix adhesion over time. Functional ameloblasts are tall, columnar, polarized cells that synthesize and secrete enamel-specific proteins. After deposition of the full thickness of enamel matrix, ameloblasts become smaller and regulate enamel maturation. Recent significant advances in the fields of molecular biology and genetics have improved our understanding of the regulatory mechanism of the ameloblast cell life cycle, mediated by the Rho family of small GTPases. They act as intracellular molecular switch that transduce signals from extracellular stimuli to the actin cytoskeleton and the nucleus. In our review, we summarize studies that provide current evidence for Rho GTPases and their involvement in ameloblast differentiation. In addition to the Rho GTPases themselves, their downstream effectors and upstream regulators have also been implicated in ameloblast differentiation.

Molecular interplay between T-Antigen and splicing factor, arginine/serine-rich 1 (SRSF1) controls JC virus gene expression in glial cells.

BackgroundHuman polyomavirus JCV is the etiologic agent of progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease characterized by lytic infection of glial cells in the central nervous system. PML is seen primarily in immunosuppressed patients and is mainly classified as an AIDS-defining disease. In addition to structural capsid proteins, JCV encodes multiple regulatory proteins, including T-antigen and agnoprotein, which are required for functional lytic infection. Previous studies have suggested that molecular interaction between viral proteins and host factors play an important role in reactivation of JCV and progression of the viral life cycle in glial cells. Recently, serine/arginine rich splicing factor 1 (SRSF1), a cellular alternative splicing factor, was identified as a strong negative regulator of JCV in glial cells. SRSF1 inhibits JCV gene expression and viral replication by directly interacting with viral promoter sequences. Here, we have investigated possible impact of JCV regulatory proteins, T-antigen and agnoprotein, on SRSF1-mediated suppression of JCV gene expression in glial cells.ResultsReporter gene analysis has suggested that T-antigen rescues viral transcriptional suppression mediated by SRSF1. Further analyses have revealed that T-antigen promotes viral gene expression by suppressing SRSF1 gene transcription in glial cells. A subsequent ChIP analysis revealed that T-antigen associates with the promoter region of SRSF1 to induce the transcriptional suppression.ConclusionsThese findings have revealed a molecular interplay between cellular SRSF1 and viral T-antigen in controlling JCV gene expression, and may suggest a novel mechanism of JCV reactivation in patients who are at risk of developing PML.

Mitotic catastrophe and cancer drug resistance: A link that must to be broken

An increased tendency of genomic alterations during the life cycle of cells leads to genomic instability, which is a major driving force for tumorigenesis. A considerable fraction of tumor cells are tetraploid or aneuploid, which renders them intrinsically susceptible to mitotic aberrations, and hence, are particularly sensitive to the induction of mitotic catastrophe. Resistance to cell death is also closely linked to genomic instability, as it enables malignant cells to expand even in a stressful environment. Currently it is known that cells can die via multiple mechanisms. Mitotic catastrophe represents a step preceding apoptosis or necrosis, depending on the expression and/or proper function of several proteins. Mitotic catastrophe was proposed to be an onco-suppressive mechanism and the evasion of mitotic catastrophe constitutes one of the gateways to cancer development. Thus, stimulation of mitotic catastrophe appears to be a promising strategy in cancer treatment. Indeed, several chemotherapeutic drugs are currently used at concentrations that induce apoptosis irrespective of the cell cycle phase, yet are very efficient at triggering mitotic catastrophe at lower doses, significantly limiting side effects. In the present review we summarize current data concerning the role of mitotic catastrophe in cancer drug resistance and discuss novel strategies to break this link.

Systemic Delivery of Anti-miRNA for Suppression of Triple Negative Breast Cancer Utilizing RNA Nanotechnology.

MicroRNAs play important roles in regulating the gene expression and life cycle of cancer cells. In particular, miR-21, an oncogenic miRNA is a major player involved in tumor initiation, progression, invasion and metastasis in several cancers, including triple negative breast cancer (TNBC). However, delivery of therapeutic miRNA or anti-miRNA specifically into cancer cells in vivo without collateral damage to healthy cells remains challenging. We report here the application of RNA nanotechnology for specific and efficient delivery of anti-miR-21 to block the growth of TNBC in orthotopic mouse models. The 15 nm therapeutic RNA nanoparticles contains the 58-nucleotide (nt) phi29 pRNA-3WJ as a core, a 8-nt sequence complementary to the seed region of miR-21, and a 39-nt epidermal growth factor receptor (EGFR) targeting aptamer for internalizing RNA nanoparticles into cancer cells via receptor mediated endocytosis. The RNase resistant and thermodynamically stable RNA nanoparticles remained intact after systemic injection into mice and strongly bound to tumors with little or no accumulation in healthy organs 8 h postinjection, and subsequently repressed tumor growth at low doses. The observed specific cancer targeting and tumor regression is a result of several key attributes of RNA nanoparticles: anionic charge which disallows nonspecific passage across negatively charged cell membrane; “active” targeting using RNA aptamers which increases the homing of RNA nanoparticles to cancer cells; nanoscale size and shape which avoids rapid renal clearance and engulfment by lung macrophages and liver Kupffer cells; favorable biodistribution profiles with little accumulation in healthy organs, which minimizes nonspecific side effects; and favorable pharmacokinetic profiles with extended in vivo half-life. The results demonstrate the clinical potentials of RNA nanotechnology based platform to deliver miRNA based therapeutics for cancer treatment.

Fundamentos de la citología diagnóstica en la neoplasia cervical preclínica

Los distintos tejidos que componen el organismo humano han sido clasificados por Bizzozero en perennes, estables y lábiles, de acuerdo al ciclo vital de las células que contienen. Los tejidos perennes están constituidos por células altamente diferenciadas que aparecen durante el crecimiento embrionario y fetal y que en condiciones fisiológicas no se multiplican ni mueren durante toda la vida extrauterina del individuo. Las neuronas del sistema nervioso central son representativas de este tipo de tejido que también han recibido el nombre de poblaciones celulares estáticas, porque la· cantidad total de ADN que contienen, permanece constante durante la vida.

Porcine retinal cell line VIDO R1 and Chlamydia suis to modelize ocular chlamydiosis

Human ocular Chlamydia trachomatis infections can lead to trachoma, the major cause of infectious blindness worldwide. Trachoma control strategies are very helpful but logistically challenging, and a trachoma vaccine is needed but not available. Pigs are a valuable large animal model for various immunological questions and could facilitate the study of human ocular chlamydial infections. In addition, a recent study identified the zoonotic potential of Chlamydia suis, the natural pathogen of pigs. In terms of the One Health Initiative, understanding the host–pathogen-interactions and finding a vaccine for porcine chlamydia infections would also benefit human health. Thus, we infected the porcine retinal cell line VIDO R1 with C. suis and analyzed the chlamydial life cycle and the innate immune response of the infected cells. Our results indicate that C. suis completes its life cycle in VIDO R1 cells within 48h, comparable to C. trachomatis in humans. C. suis infection of VIDO R1 cells led to increased levels of various innate immune mediators like pathogen recognition receptors, cytokines and chemokines including IL6, TNFα, and MMP9, also most relevant in human C. trachomatis infections. These results illustrate the first steps in the host–pathogen-interactions of ocular C. suis infections in pigs and show their similarity to C. trachomatis infections in humans, justifying further testing of pigs as an animal model for human trachoma.

Mycophenolic acid induces apoptosis of hepatic stellate cells in an in vitro model of HCV

Introduction. Hepatitis C virus (HCV) infection is an important risk factor for the development of liver fibrosis and progression to cirrhosis. Liver transplantation as terminal treatment option for liver disease requires life-long immunosuppression. However, immunomodulatory therapy may promote reinfection and renewed fibrogenesis. Immunosupressive agents may also affect the life cycle of hepatic stellate cells (HSC), the main source of extracellular matrix. We thus aimed to characterize the effects of three common immunosuppressive agents on HSC apoptosis with or without engulfment of HCV infected apoptotic bodies.Material and methods. LX2 cells were incubated with three different immunosuppressants (rapamycine, mycophenolic acid or cyclosporine A) and co-incubated for 24 and 48 h with apoptotic bodies (AB), produced from Huh7 cells or from Con1 cells (Huh7-cells containing a subgenomic HCV replicon). The engulfment of AB was confirmed by immunofluorescence staining. HSC viability, apoptosis rate and expression of profibrogenic and proapoptotic genes were quantified.Results. In LX2 cells that engulfed Conl AB, the treatment with mycophenolic acid induced HSC apoptosis and reduced collagen lalpha 1 expression compared to cylosporine A or rapamycine treatment. In conclusion mycophenolic acid is a potent inducer of HSC apoptosis and attenuates HSC activation and consecutively fibrogenesis in HCV infection. Translational studies will need to confirm these mono-culture results in vivo.

Redox-Responsive Fluorescent Probes with Different Design Strategies.

In an aerobic organism, reactive oxygen species (ROS) are an inevitable metabolic byproduct. Endogenously produced ROS have a significant role in physiological processes, but excess ROS can cause oxidative stress and can damage tissue. Cells possess elaborate mechanisms to regulate their internal redox status. The intracellular redox homeostasis plays an essential role in maintaining cellular function. However, moderate alterations in redox balance can accompany major transitions in a cell's life cycle. Because of the role of ROS in physiology and in pathology, researchers need new tools to study redox chemistry in biological systems.In recent years, researchers have made remarkable progress in developing new, highly sensitive and selective fluorescent probes that respond to redox changes, and in this Account we highlight related research, primarily from our own group. We present an overview of the design, photophysical properties, and fluorescence transduction mechanisms of reported molecules that probe redox changes. We have designed and synthesized a series of fluorescent probes for redox cycles in biological systems relying on the active center of glutathione peroxidase (GPx). We have also constructed probes based on the oxidation and reduction of hydroquinone and of 2,2,6,6-tetramethylpiperidinooxy (TEMPO). Most of these probes exhibit high sensitivity and good selectivity, absorb in the near-infrared, and respond rapidly. Such probes are useful for confocal fluorescence microscopy, a dynamic imaging technique that could allow researchers to observe biologically important ROS and antioxidants in real time. This technique and these probes provide potentially useful tools for exploring the generation, transport, physiological function, and pathogenic mechanisms of ROS and antioxidants.We also describe features that could improve the properties of redox-responsive fluorescent probes: greater photostability; rapid, dynamic, cyclic and ratiometric responses; and broader absorption in the near-IR region. In addition, fluorescent probes that include organochalcogens such as selenium and tellurium show promise for a new class of fluorescent redox probes that are both chemically stable and robustly reversible. However, further investigations of the chemical and fluorescence transduction mechanisms of selenium-based probes in response to ROS are needed.

Characterization of resistance to rhabdovirus and retrovirus infection in a human myeloid cell line.

Viruses interact with various permissive and restrictive factors in host cells throughout their replication cycle. Cell lines that are non-permissive to viral infection have been particularly useful in discovering host cell proteins involved in viral life cycles. Here we describe the characterization of a human myeloid leukemia cell line, KG-1, that is resistant to infection by retroviruses and a Rhabdovirus. We show that KG-1 cells are resistant to infection by Vesicular Stomatits Virus as well as VSV Glycoprotein (VSVG) pseudotyped retroviruses due to a defect in binding. Moreover our results indicate that entry by xenotropic retroviral envelope glycoprotein RD114 is impaired in KG-1 cells. Finally we characterize a post- entry block in the early phase of the retroviral life cycle in KG-1 cells that renders the cell line refractory to infection. This cell line will have utility in discovering proteins involved in infection by VSV and HIV-1.

The 5' untranslated region of a novel infectious molecular clone of the dicistrovirus cricket paralysis virus modulates infection.

Dicistroviridae are a family of RNA viruses that possesses a single-stranded positive-sense RNA genome containing two distinct open reading frames (ORFs), each preceded by an internal ribosome entry site that drives translation of the viral structural and nonstructural proteins, respectively. The type species, Cricket paralysis virus (CrPV), has served as a model for studying host-virus interactions; however, investigations into the molecular mechanisms of CrPV and other dicistroviruses have been limited as an established infectious clone was elusive. Here, we report the construction of an infectious molecular clone of CrPV. Transfection of in vitro-transcribed RNA from the CrPV clone into Drosophila Schneider line 2 (S2) cells resulted in cytopathic effects, viral RNA accumulation, detection of negative-sense viral RNA, and expression of viral proteins. Transmission electron microscopy, viral titers, and immunofluorescence-coupled transwell assays demonstrated that infectious viral particles are released from transfected cells. In contrast, mutant clones containing stop codons in either ORF decreased virus infectivity. Injection of adult Drosophila flies with virus derived from CrPV clones but not UV-inactivated clones resulted in mortality. Molecular analysis of the CrPV clone revealed a 196-nucleotide duplication within its 5' untranslated region (UTR) that stimulated translation of reporter constructs. In cells infected with the CrPV clone, the duplication inhibited viral infectivity yet did not affect viral translation or RNA accumulation, suggesting an effect on viral packaging or entry. The generation of the CrPV infectious clone provides a powerful tool for investigating the viral life cycle and pathogenesis of dicistroviruses and may further understanding of fundamental host-virus interactions in insect cells. Dicistroviridae, which are RNA viruses that infect arthropods, have served as a model to gain insights into fundamental host-virus interactions in insect cells. Further insights into the viral molecular mechanisms are hampered due to a lack of an established infectious clone. We report the construction of the first infectious clone of the dicistrovirus, cricket paralysis virus (CrPV). We show that transfection of the CrPV clone RNA into Drosophila cells led to production of infectious particles that resemble natural CrPV virions and result in cytopathic effects and expression of CrPV proteins and RNA in infected cells. The CrPV clone should provide insights into the dicistrovirus life cycle and host-virus interactions in insect cells. Using this clone, we find that a 196-nucleotide duplication within the 5' untranslated region of the CrPV clone increased viral translation in reporter constructs but decreased virus infectivity, thus revealing a balance that interplays between viral translation and replication.

Forced unraveling of chromatin fibers with nonuniform linker DNA lengths

The chromatin fiber undergoes significant structural changes during the cell's life cycle to modulate DNA accessibility. Detailed mechanisms of such structural transformations of chromatin fibers as affected by various internal and external conditions such as the ionic conditions of the medium, the linker DNA length, and the presence of linker histones, constitute an open challenge. Here we utilize Monte Carlo (MC) simulations of a coarse grained model of chromatin with nonuniform linker DNA lengths as found in vivo to help explain some aspects of this challenge. We investigate the unfolding mechanisms of chromatin fibers with alternating linker lengths of 26–62 bp and 44–79 bp using a series of end-to-end stretching trajectories with and without linker histones and compare results to uniform-linker-length fibers. We find that linker histones increase overall resistance of nonuniform fibers and lead to fiber unfolding with superbeads-on-a-string cluster transitions. Chromatin fibers with nonuniform linker DNA lengths display a more complex, multi-step yet smoother process of unfolding compared to their uniform counterparts, likely due to the existence of a more continuous range of nucleosome-nucleosome interactions. This finding echoes the theme that some heterogeneity in fiber component is biologically advantageous.

Interferometric measurements of dry mass content in nuclei and cytoplasm in the life cycle of antheridial filaments cells of Chara vulgaris L. in their successive developmental stages

Interferometric measurements of the nucleus and cytoplasm dry mass during interphase in the successive stages of development of antheridial filaments of <i>Chara vulgaris</i> demonstrated that the dry mass and surface area of cell nuclei double in size in each of the successive generations of the filaments, whereas neither the surface nor the dry mass of the cytoplasm increase in such proportion in the same period. In the successive stages of development of the antheridial filaments the dry mass and surface area of the nuclei and cytoplasm gradually diminish.

How long does it take a cell to divide?

This is one of the oldest questions asked in cell biology. Some bacterial cells can divide in as few as 20 min. The life cycle of many mammalian cells in culture takes >10 h to complete. One of the earliest techniques for determining cell growth rates is by measuring the number of cells in a culture versus time. The number of adherent cells can be measured at inoculation of a culture and again at a single succeeding time point. For suspension cultures, the culture can be sampled at numerous time points to provide a better estimate of the growth rate. These methods assume that all of the cells are playing the game, that is, that they are all growing and that none are in Go or are dying/dead. Newer methods focus on labeling of molecules within cells that are associated with specific stages of the cell cycle 1-4. The article by Summers et al. appearing in this issue of Cytometry Part A (page 385) presents a novel approach to determining cell division times. It involves recording over time a series of images of a field in a monolayer cell culture, identifying mitotic cells, and applying a non-homogeneous Poisson-based analysis to determine the inter-mitotic times. Low magnification images of a region of cells growing in a tissue culture flask are recorded at 15 min intervals. The only information extracted from the images is the presence and location of mitotic cells. This is accomplished by identifying the morphology of the mitotic cells, which is circular, as they lift off of the surface of the dish. The circular morphology is easily recognized manually as it uniquely identifies mitotic cells. An image analysis protocol was also developed to automate identification of the mitotic cells. It located 87% of the mitotic cells found manually. This approach eliminates tedious analytical methods often necessary to extract biologically relevant information from cellular images. The second novel aspect of this article is the analytical procedure—non-homogeneous Poisson time series analysis—used to determine the inter-mitotic times. When cytometrists think of Poisson statistics they usually think of counting statistics: the standard deviation of the number of events. That measure of uncertainty is applicable to the number of counts in each channel of a histogram—be it univariate or bivariate. However, that is not the Poisson statistical analysis used in this article. In order to understand the non-homogeneous Poisson analysis, it is illustrative to first describe a situation in which homogeneous Poisson analysis applies. A homogeneous Poisson process is one in which events occur at a non-varying rate and there is no memory in the system, i.e., the events are independent. An example of this is the decay of a very large number of radioactive nuclei with a very long lifetime. The decay rate is constant over the course of any measurement. The data recorded are the times of detected decay events. The lifetime is then determined by forming the distribution of times between detected decays. This time interval distribution is a negative exponential whose exponent is proportional to the radioactive lifetime. Thus, it is possible to measure very long lifetimes by recording the times of detected decays and transforming that data into an inter-time distribution. Direct measurement of the decay rate is impossible for long lifetimes, say a million years. For a phenomenon described by a non-homogeneous Poisson time series, the event rate is not constant. For the data analyzed in this article, the time series of the appearance of mitotic figures in a cell culture, the rate of detection of the mitotic figures increases with time as the measurements progress. That is, the event rate is not constant over time and the homogeneous Poisson approach does not apply. The analysis presented determines the inter-mitotic division times and is used to detect cell synchronization and quantify the degree of synchronization. What future developments might we expect? In the area of data acquisition, a fully automated identification of mitotic figures with 100% efficiency should be possible 5-7. The mitotic cell detection method presented is only applicable to growth of cells attached to a substrate. What about suspension cultures? By sequentially analyzing a fixed volume of such a culture by flow cytometry and identifying the mitotic cells, a similar analysis could be performed.

Virus evolution toward limited dependence on nonessential functions of the host: the case of bacteriophage SPP1.

All viruses are obligate intracellular parasites and depend on certain host cell functions for multiplication. However, the extent of such dependence and the exact nature of the functions provided by the host cell remain poorly understood. Here, we investigated if nonessential Bacillus subtilis genes are necessary for multiplication of bacteriophage SPP1. Screening of a collection of 2,514 single-gene knockouts of nonessential B. subtilis genes yielded only a few genes necessary for efficient SPP1 propagation. Among these were genes belonging to the yuk operon, which codes for the Esat-6-like secretion system, including the SPP1 receptor protein YueB. In addition, we found that SPP1 multiplication was negatively affected by the absence of two other genes, putB and efp. The gene efp encodes elongation factor P, which enhances ribosome activity by alleviating translational stalling during the synthesis of polyproline-containing proteins. PutB is an enzyme involved in the proline degradation pathway that is required for infection in the post-exponential growth phase of B. subtilis, when the bacterium undergoes a complex genetic reprogramming. The putB knockout shortens significantly the window of opportunity for SPP1 infection during the host cell life cycle. This window is a critical parameter for competitive phage multiplication in the soil environment, where B. subtilis rarely meets conditions for exponential growth. Our results in combination with those reported for other virus-host systems suggest that bacterial viruses have evolved toward limited dependence on nonessential host functions. A successful viral infection largely depends on the ability of the virus to hijack cellular machineries and to redirect the flow of building blocks and energy resources toward viral progeny production. However, the specific virus-host interactions underlying this fundamental transformation are poorly understood. Here, we report on the first systematic analysis of virus-host cross talk during bacteriophage infection in Gram-positive bacteria. We show that lytic bacteriophage SPP1 is remarkably independent of nonessential genes of its host, Bacillus subtilis, with only a few cellular genes being necessary for efficient phage propagation. We hypothesize that such limited dependence of the virus on its host results from a constant "evolutionary arms race" and might be much more widespread than currently thought.

Asociación de excreción urinaria de sodio y potasio con la presión arterial

Reovirus not only causes considerable economic loss in the swine industry of the United States and other countries, but also threatens the public health due to its zoonotic potential. According to previous reports, LiCl has antiviral activity against a number of viruses. The inhibitory effects of LiCl on reovirus life cycle in Vero cells were evaluated. The unpaired t-test and one-way ANOVA were used to analyze the differences between experimental groups. We first found that LiCl treatment significantly inhibited reovirus replication in a dose-dependent manner. Furthermore, we found that this antiviral activity of LiCl targets the early stage of viral replication. LiCl could be a potential drug against reovirus infection.