Arrest Of Cell Division Research Articles

Use of Time Lapse Microscopy to Visualize Anoxia-induced Suspended Animation in <em>C. elegans</em> Embryos

Caenorhabdits elegans has been used extensively in the study of stress resistance, which is facilitated by the transparency of the adult and embryo stages as well as by the availability of genetic mutants and transgenic strains expressing a myriad of fusion proteins(1-4). In addition, dynamic processes such as cell division can be viewed using fluorescently labeled reporter proteins. The study of mitosis can be facilitated through the use of time-lapse experiments in various systems including intact organisms; thus the early C. elegans embryo is well suited for this study. Presented here is a technique by which in vivo imaging of sub-cellular structures in response to anoxic (99.999% N2; <2 ppm O2) stress is possible using a simple gas flow through setup on a high-powered microscope. A microincubation chamber is used in conjunction with nitrogen gas flow through and a spinning disc confocal microscope to create a controlled environment in which animals can be imaged in vivo. Using GFP-tagged gamma tubulin and histone, the dynamics and arrest of cell division can be monitored before, during and after exposure to an oxygen-deprived environment. The results of this technique are high resolution, detailed videos and images of cellular structures within blastomeres of embryos exposed to oxygen deprivation.

Lectin-like Oxidized Low-density Lipoprotein Receptor-1 (LOX-1) and Cardiac Fibroblast Growth

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) regulates growth of a variety of cells and is important in inflammation, oxidative stress, and tissue remodeling. Recent studies show that LOX-1 deletion limits cardiac remodeling after sustained hypertension. We posited that LOX-1 may affect cardiac fibroblast growth and collagen secretion. To examine this postulate, we studied growth pattern of cardiac fibroblasts from hearts of wild-type and LOX-1 knockout (KO) mice. LOX-1 KO fibroblasts exhibited dramatically reduced growth when compared with wild-type mice fibroblasts and became much larger than wild-type mice fibroblasts in serial cultures, suggesting arrest of cell division. Western blotting and immunofluorescence showed that cell division control protein 42, a key regulator for cell division, was markedly downregulated in LOX-1 KO fibroblasts. The cytoskeletal organization in these fibroblasts was significantly altered in strand orientation, and some fibroblasts were completely devoid of F-actin. Furthermore, NADPH oxidase expression and generation of reactive oxygen species, as well as cell proliferation signals serine/threonine-specific protein kinase and murine double minute 2, were significantly reduced in LOX-1 KO fibroblasts. To confirm the essential role of LOX-1 in fibroblast growth, LOX-1 KO fibroblasts were transfected with h-LOX-1 cDNA. After transfection, the altered pattern of cytoskeletal organization, as well as expression of cell division control protein 42, serine/threonine-specific protein kinase, and murine double minute 2, was normalized. In congruent with these in vitro data, we found that the cardiac fibroblast number and expression of fibronectin and procoallagen-1/collagen were significantly lower in hypertensive LOX-1 KO mice hearts than in hypertensive wild-type mice hearts subjected to sustained hypertension (angiotensin II infusion). These findings implicate LOX-1 in cytoskeletal organization and growth of cardiac fibroblasts.

Signaling Pathways that Regulate Cell Division

Cell division requires careful orchestration of three major events: entry into mitosis, chromosomal segregation, and cytokinesis. Signaling within and between the molecules that control these events allows for their coordination via checkpoints, a specific class of signaling pathways that ensure the dependency of cell-cycle events on the successful completion of preceding events. Multiple positive- and negative-feedback loops ensure that a cell is fully committed to division and that the events occur in the proper order. Unlike other signaling pathways, which integrate external inputs to decide whether to execute a given process, signaling at cell division is largely dedicated to completing a decision made in G1 phase-to initiate and complete a round of mitotic cell division. Instead of deciding if the events of cell division will take place, these signaling pathways entrain these events to the activation of the cell-cycle kinase cyclin-dependent kinase 1 (CDK1) and provide the opportunity for checkpoint proteins to arrest cell division if things go wrong.

Vascular endothelial growth factor and HDAC 6: a neuroprotective signalling pathway against cancer therapy-induced neuropathy

In the context of treatments for cancer, the use of chemotherapeutic agents focuses on arresting cell division, anti-angiogenesis and targeting mechanisms responsible for metastasis. For that purpose, treatments are designed to manipulate molecules that impair each of these processes by inhibition of signalling pathways and growth factor receptors, as well as changing the dynamics of cytoskeletal proteins involved in cell division and migration. However, chemotherapeutic drugs affect not only tumour cells but also the physiology of other host tissues, including neurons: specifically, anti-cancer drugs exert direct and indirect effects on sensory nerves. Peripheral neuropathies result from dysregulation of mechanisms controlling neuronal physiology and myelination. Toxic neuropathies caused by chemotherapeutic agents are prominent amongst the many genetic and non-genetic causes of neuropathy (von Hehn et al. , 2012). The mechanisms involved in neuropathy associated with the use of paclitaxel include terminal arbour degeneration, mitochondrial changes, inflammation, activation of calpain and caspases and changes in the expression and function of calcium, sodium and potassium voltage-gated ionic channels (Jaggi and Singh, 2012). These changes may predispose to profound loss of motor and sensory function with pain. Paclitaxel binds to beta-tubulin and stabilizes its polymerization, disrupting the dynamics of microtubules, arresting cell division and activating apoptotic pathways. Paclitaxel also increases tubulin acetylation, which has several consequences on physiological and pathological processes (Polomano et al. , 2001). Tubulin acetylation impacts on subcellular organelles, and vesicular traffic and signalling that control the localization and movement of plasma membrane proteins (Janke …

Discrimination of Ligands with Different Flexibilities Resulting from the Plasticity of the Binding Site in Tubulin

Tubulin, an α,β heterodimer, has four distinct ligand binding sites (for paclitaxel, peloruside/laulimalide, vinca, and colchicine). The site where colchicine binds is a promising drug target for arresting cell division and has been observed to accommodate compounds that are structurally diverse but possess comparable affinity. This investigation, using two such structurally different ligands as probes (one being colchicine itself and another, TN16), aims to provide insight into the origin of this diverse acceptability to provide a better perspective for the design of novel therapeutic molecules. Thermodynamic measurements reveal interesting interplay between entropy and enthalpy. Although both these parameters are favourable for TN16 binding (ΔH < 0, ΔS > 0), but the magnitude of entropy has the determining role for colchicine binding as its enthalpic component is destabilizing (ΔH > 0, ΔS > 0). Molecular dynamics simulation provides atomistic insight into the mechanism, pointing to the inherent flexibility of the binding pocket that can drastically change its shape depending on the ligand that it accepts. Simulation shows that in the complexed states both the ligands have freedom to move within the binding pocket; colchicine can switch its interactions like a "flying trapeze", whereas TN16 rocks like a "swing cradle", both benefiting entropically, although in two different ways. Additionally, the experimental results with respect to the role of solvation entropy correlate well with the computed difference in the hydration: water molecules associated with the ligands are released upon complexation. The complementary role of van der Waals packing versus flexibility controls the entropy-enthalpy modulations. This analysis provides lessons for the design of new ligands that should balance between the "better fit" and "flexibility"', instead of focusing only on the receptor-ligand interactions.

Rationalization of paclitaxel insensitivity of yeast β-tubulin and human βIII-tubulin isotype using principal component analysis

BackgroundThe chemotherapeutic agent paclitaxel arrests cell division by binding to the hetero-dimeric protein tubulin. Subtle differences in tubulin sequences, across eukaryotes and among β-tubulin isotypes, can have profound impact on paclitaxel-tubulin binding. To capture the experimentally observed paclitaxel-resistance of human βIII tubulin isotype and yeast β-tubulin, within a common theoretical framework, we have performed structural principal component analyses of β-tubulin sequences across eukaryotes.ResultsThe paclitaxel-resistance of human βIII tubulin isotype and yeast β-tubulin uniquely mapped on to the lowest two principal components, defining the paclitaxel-binding site residues of β-tubulin. The molecular mechanisms behind paclitaxel-resistance, mediated through key residues, were identified from structural consequences of characteristic mutations that confer paclitaxel-resistance. Specifically, Ala277 in βIII isotype was shown to be crucial for paclitaxel-resistance.ConclusionsThe present analysis captures the origin of two apparently unrelated events, paclitaxel-insensitivity of yeast tubulin and human βIII tubulin isotype, through two common collective sequence vectors.

Effects of advanced glycation end-products (AGEs) on skin keratinocytes by nuclear factor-kappa B (NF-κB) activation

Advance glycation end-products (AGEs) are produced in patients with long-term hyperglycemia metabolic disorder and responsible for multiple symptoms including impaired wound healing. This study was designed to reveal the roles and possible mechanism of AGE in diabetic wound healing. Sixteen Sprague-Dawley (SD) rats were divided into two groups randomly; the streptozotocin (STZ) induced diabetic group and the normal group. Eight weeks later, epidermal growth factor (EGF) and AGE levels, nuclear factor-kappa B (NF-κB) localization and cell viability were measured in vivo. Keratinocytes from normal skin were cultured in AGE-enriched conditional media, and the cell viability, apoptosis, adhesion and migration were detected in order to find the directed evidence between AGE and keratinocytes. AGE content was higher and NF-κB expression was more localized in the nuclear of keratinocytes in diabetic skins. AGE could inhibit normal cell growth by inducing apoptosis and arresting cell division cycle, inhibiting cell adhesion and promoting migration which might be mediated by NF-κB in vitro. Blocking NF-κB activity could reverse effects of AGE on cell proliferation and migration, but not adhesion. Therefore, AGE could damage the skin keratinocytes function in vivo and in vitro, and the activation of NF-κB is involved in this process. Key words : AGE, NF-kappaB, keratinocytes, diabetes, wound healing.

Ribonuclease E Modulation of the Bacterial SOS Response

Plants, animals, bacteria, and Archaea all have evolved mechanisms to cope with environmental or cellular stress. Bacterial cells respond to the stress of DNA damage by activation of the SOS response, the canonical RecA/LexA-dependent signal transduction pathway that transcriptionally derepresses a multiplicity of genes–leading to transient arrest of cell division and initiation of DNA repair. Here we report the previously unsuspected role of E. coli endoribonuclease RNase E in regulation of the SOS response. We show that RNase E deletion or inactivation of temperature-sensitive RNase E protein precludes normal initiation of SOS. The ability of RNase E to regulate SOS is dynamic, as down regulation of RNase E following DNA damage by mitomycin C resulted in SOS termination and restoration of RNase E function leads to resumption of a previously aborted response. Overexpression of the RraA protein, which binds to the C-terminal region of RNase E and modulates the actions of degradosomes, recapitulated the effects of RNase E deficiency. Possible mechanisms for RNase E effects on SOS are discussed.

Dynamic Deposition of Histone Variant H3.3 Accompanies Developmental Remodeling of the Arabidopsis Transcriptome

In animals, replication-coupled histone H3.1 can be distinguished from replication-independent histone H3.3. H3.3 variants are enriched at active genes and their promoters. Furthermore, H3.3 is specifically incorporated upon gene activation. Histone H3 variants evolved independently in plants and animals, and it is unclear whether different replication-independent H3.3 variants developed similar properties in both phyla. We studied Arabidopsis H3 variants in order to find core properties of this class of histones. Here we present genome-wide maps of H3.3 and H3.1 enrichment and the dynamic changes of their profiles upon cell division arrest. We find H3.3 enrichment to positively correlate with gene expression and to be biased towards the transcription termination site. In contrast with H3.1, heterochromatic regions are mostly depleted of H3.3. We report that, in planta, dynamic changes in H3.3 profiles are associated with the extensive remodeling of the transcriptome that occurs during cell differentiation. We propose that H3.3 dynamics are linked to transcription and are involved in resetting covalent histone marks at a genomic scale during plant development. Our study suggests that H3 variants properties likely result from functionally convergent evolution.

Effects of increased temperature on dimethylsulfoniopropionate (DMSP) concentration and methionine synthase activity in Symbiodinium microadriaticum

Dinoflagellate algae of the genus Symbiodinium occur as endosymbionts in a variety of hosts including coral. The response of Symbiodinium spp. to environmental changes could dictate survival of their hosts and the ecological success of coral reef ecosystems. Oxidative stress has been linked to a breakdown in this symbiotic relationship, known as bleaching. Increased temperature is one of the primary environmental changes linked to this phenomenon. Preliminary studies have established high concentrations of the sulfur compound dimethylsulfoniopropionate (DMSP) in Symbiodinium spp., with increased temperature. To examine the potential use of DMSP as an antioxidant, a 5 day incubation experiment was conducted at two temperatures with the algae S. microadriaticum (CCMP1633) isolated from the cnidarian host Aiptasia pulchella. An HPLC assay for the activity of the enzyme B12-dependent methionine synthase was modified and used to determine the link between de novo production of methionine, a precursor to DMSP, and temperature induced oxidative stress. DMSP concentrations per cell increased approximately 38 % in the 33 °C treatment cultures over 120 h. However, these cells also increased more than 2-fold in biovolume (127 ± 43 %), and SYTO-BC stain indicated increased DNA content (approximately 4-fold), suggesting arrested cell division. Normalization of DMSP to biovolume revealed that the concentrations actually decreased approximately 49 % after 2 days in cultures exposed to elevated temperature (33 °C), but were not significantly different from the control treatment at 120 h (27 °C). Concomitant changes in the 33 °C treatment relative to the control (after 120 h) resulted in an approximately 8-fold increase in reactive oxygen species, a 37 % (±7 %) decrease in photosynthetic efficiency of photosystem II, and a 5-fold increase in xanthophyll cycling. Methionine synthase activity (MSA) correlated to the decrease in DMSP concentration (R 2 = 0.778), with decreasing activity at the high temperature. Given this decrease in MSA, the increase in DMSP per cell may be due to DMSP production utilizing methionine from protein turnover, and not de novo synthesis via MSA. The findings of this study provide insight into the responses of algal symbionts to environmental changes, shed light on the potential use of DMSP and other known photo-protective mechanisms such as xanthophyll cycling under temperature induced oxidative stress, and support the suspected cessation of cell division under these conditions. This information could be crucial to understanding cellular responses to environmental changes and the ability of these organisms to survive under elevated sea surface temperatures projected for the near future.

Concentration-dependent cytotoxicity of copper ions on mouse fibroblasts in vitro: effects of copper ion release from TCu380A vs TCu220C intra-uterine devices

Sustained release of copper (Cu) ions from Cu-containing intrauterine devices (CuIUD) is quite efficient for contraception. However, the tissue surrounding the CuIUD is exposed to toxic Cu ion levels. The objective for this study was to quantify the concentration dependent cytotoxic effects of Cu ions and correlate the toxicity due to Cu ion burst release for two popular T-shaped IUDs - TCu380A and TCu220C on L929 mouse fibroblasts. Fibroblasts were cultured in 98 well tissue culture plates and 3-(4,5-dimethylthiazol- 2-yl)-2,5-diphehyltetrazolium bromide (MTT) assay was used to determine their viability and proliferation as a function of time. For cell seeding numbers ranging from 10,000 to 100,000, a maximum culture time of 48 h was identified for fibroblasts without significant reduction in cell proliferation due to contact inhibition. Thus, for Cu cytotoxicity assays, a cell seeding density of 50,000 and a maximum culture time of 48 h in 96 well plates were used. 24 h after cell seeding, culture media were replaced with Cu ion containing media solutions of different concentrations, including 24 and 72 h extracts from TCuIUDs and incubated for a further 24 h. Cell viability decreased with increasing Cu ion concentration, with 30 % and 100 % reduction for 40 μg/ml and 100 μg/ml respectively at 24 h. The cytotoxic effects were further evaluated using light microscopy, apoptosis and cell cycle analysis assays. Fibroblasts became rounded and eventually detached from TCP surface due to Cu ion toxicity. A linear increase in apoptotic cell population with increasing Cu ion concentration was observed in the tested range of 0 to 50 μg/ml. Cell cycle analysis indicated the arrest of cell division for the tested 25 to 50 μg/ml Cu ion treatments. Among the TCuIUDs, TCu220C having 265 mm(2) Cu surface area released 9.08 ± 0.16 and 26.02 ± 0.25 μg/ml, while TCu380A having 400 mm(2) released 96.7 ± 0.11 and 159.3 ± 0.15 μg/ml respectively following 24 and 72 h extractions. The effects of TCuIUD extracts on viability, morphology, apoptosis and cell cycle assay on L929 mouse fibroblasts cells, were appropriate for their respective Cu ion concentrations. Thus, a concentration of about 46 μg/ml (~29 μM) was identified as the LD50 dose for L929 mouse fibroblasts when exposed for 24 h based on our MTT cell viability assay. The burst release of lethal concentration of Cu ions from TCu380A, especially at the implant site, is a cause of concern, and it is advisable to use TCuIUD designs that release Cu ions within cytotoxic limits yet therapeutic, similar to TCu220C.

Abstract 961: Pathways of tumorigenesis promoted by the growth factor progranulin in SW-13 adrenocortical carcinoma cells

Abstract Adrenocortical carcinomas are highly malignant cancers, with a very low 5 year survival rate. The SW-13 cell line originated from a stage IV adrenocortical carcinoma, but is only poorly tumorigenic in mice. It can, however, be made highly tumorigenic in vivo if it is engineered to express a limited number of growth factors including progranulin (PGRN, also called PCDGF, granulin epithelin precursor, or proepithelin) and secreted FGFs. This provides a model system to study the transition of an adrenocortical carcinoma from low to a high malignant potential. PGRN is a secreted glycoprotein growth factor that is over produced by many cancers including those of the breast, ovary, endometrium, prostate, bladder, and liver. It acts on cancer growth by increasing mitosis, decreasing apoptosis and stimulating invasion. In addition, PGRN has been implicated as a stimulator of tumor stroma growth in breast cancer. We examined the expression of PGRN in SW-13 cells at different stages of the cell cycle. Cells were synchronized using two independent agents, L-Mimosine and aphidicolin to arrest cell division. Washout of the drugs released the SW-13 cells into the cell cycles with slow (L-Mimosine) or rapid (aphidicolin) kinetics, and PGRN expression increased in parallel with the increased proportion of cells in active cell division. Depleting PGRN mRNA levels slowed reentry into the cell cycle following drug removal. Inhibition of MEK1/2, phosphatidylinositol-3 kinase (PI3K), protein kinase C (PKC) and phospholipase-C-α (PLCγ) impairs proliferation of SW-13 cells carrying only empty vector (SW-13V) with differential effects on mitosis and apoptosis. In cells with elevated PGRN, (SW-13P), the anti-proliferative effects of inhibiting MEK1/2, PI3K and PKC, but not PLCγ, are attenuated. Inhibition of the stress kinase p38 increases proliferation of SW-13V, but not SW-13P cells, suggesting that PGRN and p38 have opposing effects on proliferation. Inhibition of p38 enhances the phosphorylation of MEK1/2 in SW-13V cells, while inhibiting PKC decreases it, suggesting that PKC and p38 pathways interact with the PGRN-regulated MEK1/2 signaling cascade. Transcriptional profiling indicated that expression of PGRN modulated levels of proteins in the Wnt and Notch-signaling pathways. These results suggest that PGRN expression may be coordinated with the cell cycle, and, may promote tumorigenesis by intervening in several signaling pathways. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 961. doi:1538-7445.AM2012-961

Is cellular senescence an example of antagonistic pleiotropy?

It is generally accepted that the permanent arrest of cell division known as cellular senescence contributes to aging by an antagonistic pleiotropy mechanism: cellular senescence would act beneficially early in life by suppressing cancer, but detrimentally later on by causing frailty and, paradoxically, cancer. In this review, we show that there is room to rethink this common view. We propose a critical appraisal of the arguments commonly brought in support of it, and we qualitatively analyse published results that are of relevance to understand whether or not cellular senescence-associated genes really act in an antagonistic-pleiotropic manner in humans.

Taxol-Conjugated Pamam Dendrimers Utilize Three Modes of Action on Microtubule Structure

Paclitaxel (Taxol) is a cancer drug that causes cell death by stabilizing microtubules and consequently arresting cell division. Previously, the cytotoxicity of taxol-conjugated PAMAM dendrimers was demonstrated in cancer cells. The exact mode(s) of action responsible for the potent cytotoxicity of these dendrimers were not examined but the literature provides uncertainty that the taxol could be released from the dendrimer carrier after cellular entry. Accordingly, we asked whether the taxol-dendrimer conjugate itself is able to bind microtubules. To address this question, we investigated the effect of these conjugates on microtubules in vitro using total internal reflection fluorescence microscopy (TIRFM) and transmission electron microscopy (TEM). We find that the taxol-dendrimer conjugate affects microtubule structure in two ways: (1) the conjugate can bind tubulin during tubulin polymerization and stabilize it into a tubular structure and (2) the conjugate can bundle microtubules in a manner that is not dependent on taxol, but dendrimer electrostatics. Both of these modes of action would arrest cell division and consequently kill the cell. This is the first time that the binding of taxol-conjugated dendrimers to microtubules has been demonstrated in vitro. Furthermore, our results provide both mechanistic insights into the cytotoxicity of the previously characterized taxol-conjugated PAMAM dendrimers and additional evidence for the potential of these and similar conjugates as cancer therapeutics.

Study of Effect of Colchicine Exposure on Length of Chromosome During Mitosis

In routine karyotyping procedure from lymphocyte culture (blood culture) cells are exposed to colchicine to arrest cell division at metaphase to visualise chromosomes. Routinely duration of exposure to colchicine varies from 1 to 2 hours. To get better quality of chromosomes both the concentration and period of exposure to colchicine can be altered.While standardization of departmental Genetic/Research laboratory trial different period of exposure time of colchicine was done to get longer chromosomes with splitted chromosomes.It was observed it was marked that by shortening the exposure period of colchicine longer and better quality of chromosomes can be obtained whereas longer exposure period of colchicine gives condensed chromosomes.

Growth-Arrest-Specific Protein 2 Inhibits Cell Division in Xenopus Embryos

BackgroundGrowth-arrest-specific 2 gene was originally identified in murine fibroblasts under growth arrest conditions. Furthermore, serum stimulation of quiescent, non-dividing cells leads to the down-regulation of gas2 and results in re-entry into the cell cycle. Cytoskeleton rearrangements are critical for cell cycle progression and cell division and the Gas2 protein has been shown to co-localize with actin and microtubules in interphase mammalian cells. Despite these findings, direct evidence supporting a role for Gas2 in the mechanism of cell division has not been reported.Methodology and Principal FindingsTo determine whether the Gas2 protein plays a role in cell division, we over-expressed the full-length Gas2 protein and Gas2 truncations containing either the actin-binding CH domain or the tubulin-binding Gas2 domain in Xenopus laevis embryos. We found that both the full-length Gas2 protein and the Gas2 domain, but not the CH domain, inhibited cell division and resulted in multinucleated cells. The observation that Gas2 domain alone can arrest cell division suggests that Gas2 function is mediated by microtubule binding. Gas2 co-localized with microtubules at the cell cortex of Gas2-injected Xenopus embryos using cryo-confocal microscopy and co-sedimented with microtubules in cytoskeleton co-sedimentation assays. To investigate the mechanism of Gas2-induced cell division arrest, we showed, using a wound-induced contractile array assay, that Gas2 stabilized microtubules. Finally, electron microscopy studies demonstrated that Gas2 bundled microtubules into higher-order structures.Conclusion and SignificanceOur experiments show that Gas2 inhibits cell division in Xenopus embryos. We propose that Gas2 function is mediated by binding and bundling microtubules, leading to cell division arrest.

Targeted killing of a mammalian cell based upon its specialized metabolic state

Mouse ES cells use a mitochondrial threonine dehydrogenase (TDH) enzyme to catabolize threonine into glycine and acetyl-CoA. Measurements of mRNA abundance have given evidence that ES cells express upwards of 1,000-fold higher levels of TDH mRNA than any of seven other mouse tissues tested. When cell culture medium is deprived of threonine, ES cells rapidly discontinue DNA synthesis, arrest cell division, and eventually die. Such studies led to the conclusion that mouse ES cells exist in a threonine-dependent metabolic state. Proceeding with the assumption that the active TDH enzyme should be essential for the growth and viability of mouse ES cells, we performed a drug screen in search of specific inhibitors of the purified TDH enzyme. Such efforts led to the discovery of a class of quinazolinecarboxamide (Qc) compounds that inhibit the ability of the TDH enzyme to catabolize threonine into glycine and acetyl-CoA. Administration of Qc inhibitors of TDH to mouse ES cells impeded cell growth and resulted in the induction of autophagy. By contrast, the same chemicals failed to affect the growth of HeLa cells at concentrations 300-fold higher than that required to kill mouse ES cells. It was likewise observed that the Qc class of TDH inhibitors failed to affect the growth or viability of ES cell-derived embryoid body cells known to have extinguished TDH expression. These studies demonstrate how it is possible to kill a specific mammalian cell type on the basis of its specialized metabolic state.

Retracted: Maf acts downstream of ComGA to arrest cell division in competent cells of B. subtilis

Transformable (competent) cells of Bacillus subtilis are blocked in cell division because the traffic ATPase ComGA prevents the formation of FtsZ rings. Although ComGA-deficient cells elongate and form FtsZ rings, cell division remains blocked at a later stage and the cells become mildly filamented. Here we show that the highly conserved protein Maf is synthesized predominantly in competent cells under the direct control of the transcription factor ComK and is solely responsible for the later block in cell division. In vivo and in vitro data show that Maf binds to both ComGA and DivIVA. A point mutation in maf that interferes with Maf binding to DivIVA also interferes with the ability of Maf to inhibit cell division. Based on these findings, we propose that Maf and ComGA mediate mechanisms for the inhibition of cell division in competent cells with Maf acting downstream of ComGA. We further suggest that Maf must interact with DivIVA to inhibit cell division.

Cell division blockage: but this time by a surprisingly conserved protein

Activation of DNA repair proteins is often accompanied by an arrest in cell division. Several proteins have been identified that regulate the division blockage associated with the SOS response. When Bacillus subtilis cells become genetically competent they also activate DNA repair proteins and stop dividing. In this issue of Molecular Microbiology, Briley et al., 2011 describe a new protein involved in this process. This protein, Maf, does not prevent FtsZ polymerization, but it inhibits synthesis of the division septum. What is fascinating about Maf is that it is conserved and can be found in all kingdoms of life.

The Smc5/6 complex and the difficulties cutting the ties of twin sisters

The Smc5/6 complex and the difficulties cutting the ties of twin sisters