Geometric control of cell life and death

Human and bovine capillary endothelial cells were switched from growth to apoptosis by using micropatterned substrates that contained extracellular matrix-coated adhesive islands of decreasing size to progressively restrict cell extension. Cell spreading also was varied while maintaining the total cell-matrix contact area constant by changing the spacing between multiple focal adhesion-sized islands. Cell shape was found to govern whether individual cells grow or die, regardless of the type of matrix protein or antibody to integrin used to mediate adhesion. Local geometric control of cell growth and viability may therefore represent a fundamental mechanism for developmental regulation within the tissue microenvironment.

Observation of Gravitational Waves from a Binary Black Hole Merger

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

Immune response in mice that lack the interferon-gamma receptor

Interferon-gamma (IFN-gamma) exerts pleiotropic effects, including antiviral activity, stimulation of macrophages and natural killer cells, and increased expression of major histocompatibility complex antigens. Mice without the IFN-gamma receptor had no overt anomalies, and their immune system appeared to develop normally. However, mutant mice had a defective natural resistance, they had increased susceptibility to infection by Listeria monocytogenes and vaccinia virus despite normal cytotoxic and T helper cell responses. Immunoglobulin isotype analysis revealed that IFN-gamma is necessary for a normal antigen-specific immunoglobulin G2a response. These mutant mice offer the possibility for the further elucidation of IFN-gamma-mediated functions by transgenic cell- or tissue-specific reconstitution of a functional receptor.

Neurodegeneration, myocardial injury, and perinatal death in mitochondrial superoxide dismutase-deficient mice

Manganese superoxide dismutase (SOD2) converts superoxide to oxygen plus hydrogen peroxide and serves as the primary defense against mitochondrial superoxide. Impaired SOD2 activity in humans has been associated with several chronic diseases, including ovarian cancer and type I diabetes, and SOD2 overexpression appears to suppress malignancy in cultured cells. We have produced a line of SOD2 knockout mice (SOD2m1BCM/SOD2m1BCM) that survive up to 3 weeks of age and exhibit several novel pathologic phenotypes including severe anemia, degeneration of neurons in the basal ganglia and brainstem, and progressive motor disturbances characterized by weakness, rapid fatigue, and circling behavior. In addition, SOD2m1BCM/SOD2m1BCM mice older than 7 days exhibit extensive mitochondrial injury within degenerating neurons and cardiac myocytes. Approximately 10% of SOD2m1BCM/SOD2m1BCM mice exhibit markedly enlarged and dilated hearts. These observations indicate that SOD2 deficiency causes increased susceptibility to oxidative mitochondrial injury in central nervous system neurons, cardiac myocytes, and other metabolically active tissues after postnatal exposure to ambient oxygen concentrations. Our SOD2-deficient mice differ from a recently described model in which homozygotes die within the first 5 days of life with severe cardiomyopathy and do not exhibit motor disturbances, central nervous system injury, or ultrastructural evidence of mitochondrial injury.

Cardiac muscle cell hypertrophy and apoptosis induced by distinct members of the p38 mitogen-activated protein kinase family

p38 mitogen-activated protein (MAP) kinase activities were significantly increased in mouse hearts after chronic transverse aortic constriction, coincident with the onset of ventricular hypertrophy. Infection of cardiomyocytes with adenoviral vectors expressing upstream activators for the p38 kinases, activated mutants of MAP kinase kinase 3b(E) (MKK3bE) and MAP kinase kinase 6b(E) (MKK6bE), elicited characteristic hypertrophic responses, including an increase in cell size, enhanced sarcomeric organization, and elevated atrial natriuretic factor expression. Overexpression of the activated MKK3bE in cardiomyocytes also led to an increase in apoptosis. The hypertrophic response was enhanced by co-infection of an adenoviral vector expressing wild type p38 beta, and was suppressed by the p38 beta dominant negative mutant. In contrast, the MKK3bE-induced cell death was increased by co-infection of an adenovirus expressing wild type p38 alpha, and was suppressed by the dominant negative p38 alpha mutant. This provides the first evidence in any cell system for divergent physiological functions for different members of the p38 MAP kinase family. The direct involvement of p38 pathways in cardiac hypertrophy and apoptosis suggests a significant role for p38 signaling in the pathophysiology of heart failure.

The structural and mechanical complexity of cell-growth control

Tight control of cell proliferation is required to ensure normal tissue patterning and prevent cancer formation. The analysis of cultured cells has led to an explosion in our understanding of the molecules that trigger growth and mediate cell-cycle progression. However, the mechanism by which the local growth differentials that drive morphogenesis are established and maintained still remains unknown. Here we review recent work that reveals the importance of cell binding to the extracellular matrix, and associated changes in cell shape and cytoskeletal tension, to the spatial control of cell-cycle progression. These findings change the paradigm of cell-growth control, by placing our understanding of molecular signalling cascades in the context of the structural and mechanical complexity of living tissues.

How a protein binds B12: A 3.0 A X-ray structure of B12-binding domains of methionine synthase

The crystal structure of a 27-kilodalton methylcobalamin-containing fragment of methionine synthase from Escherichia coli was determined at 3.0 A resolution. This structure depicts cobalamin-protein interactions and reveals that the corrin macrocycle lies between a helical amino-terminal domain and an alpha/beta carboxyl-terminal domain that is a variant of the Rossmann fold. Methylcobalamin undergoes a conformational change on binding the protein; the dimethylbenzimidazole group, which is coordinated to the cobalt in the free cofactor, moves away from the corrin and is replaced by a histidine contributed by the protein. The sequence Asp-X-His-X-X-Gly, which contains this histidine ligand, is conserved in the adenosylcobalamin-dependent enzymes methylmalonyl-coenzyme A mutase and glutamate mutase, suggesting that displacement of the dimethylbenzimidazole will be a feature common to many cobalamin-binding proteins. Thus the cobalt ligand, His759, and the neighboring residues Asp757 and Ser810, may form a catalytic quartet, Co-His-Asp-Ser, that modulates the reactivity of the B12 prosthetic group in methionine synthase.

Micropatterned surfaces for control of cell shape, position, and function

The control of cell position and function is a fundamental focus in the development of applications ranging from cellular biosensors to tissue engineering. Using microcontact printing of self-assembled monolayers (SAMs) of alkanethiolates on gold, we manufactured substrates that contained micrometer-scale islands of extracellular matrix (ECM) separated by nonadhesive regions such that the pattern of islands determined the distribution and position of bovine and human endothelial cells. In addition, the size and geometry of the islands were shown to control cell shape. Traditional approaches to modulate cell shape, either by attaching suspended cells to microbeads of different sizes or by plating cells on substrates coated with different densities of ECM, suggested that cell shape may play an important role in control of apoptosis as well as growth. Data are presented which show how micropatterned substrates were used to definitively test this hypothesis. Progressively restricting bovine and human endothelial cell extension by culturing cells on smaller and smaller micropatterned adhesive islands regulated a transition from growth to apoptosis on a single continuum of cell spreading, thus confirming the central role of cell shape in cell function. The micropatterning technology is therefore essential not only for construction of biosurface devices but also for the investigation of the fundamental biology of cell-ECM interactions.

Shape-dependent control of cell growth, differentiation, and apoptosis: switching between attractors in cell regulatory networks

Development of characteristic tissue patterns requires that individual cells be switched locally between different phenotypes or "fates;" while one cell may proliferate, its neighbors may differentiate or die. Recent studies have revealed that local switching between these different gene programs is controlled through interplay between soluble growth factors, insoluble extracellular matrix molecules, and mechanical forces which produce cell shape distortion. Although the precise molecular basis remains unknown, shape-dependent control of cell growth and function appears to be mediated by tension-dependent changes in the actin cytoskeleton. However, the question remains: how can a generalized physical stimulus, such as cell distortion, activate the same set of genes and signaling proteins that are triggered by molecules which bind to specific cell surface receptors. In this article, we use computer simulations based on dynamic Boolean networks to show that the different cell fates that a particular cell can exhibit may represent a preprogrammed set of common end programs or "attractors" which self-organize within the cell's regulatory networks. In this type of dynamic network model of information processing, generalized stimuli (e.g., mechanical forces) and specific molecular cues elicit signals which follow different trajectories, but eventually converge onto one of a small set of common end programs (growth, quiescence, differentiation, apoptosis, etc.). In other words, if cells use this type of information processing system, then control of cell function would involve selection of preexisting (latent) behavioral modes of the cell, rather than instruction by specific binding molecules. Importantly, the results of the computer simulation closely mimic experimental data obtained with living endothelial cells. The major implication of this finding is that current methods used for analysis of cell function that rely on characterization of linear signaling pathways or clusters of genes with common activity profiles may overlook the most critical features of cellular information processing which normally determine how signal specificity is established and maintained in living cells.

Blockade of NF-kappaB activity in human prostate cancer cells is associated with suppression of angiogenesis, invasion, and metastasis

Since the NF-kappaB/relA transcription factor is constitutively activated in human prostate cancer cells, we determined whether blocking NF-kappaB/relA activity in human prostate cancer cells affected their angiogenesis, growth, and metastasis in an orthotopic nude mouse model. Highly metastatic PC-3M human prostate cancer cells were transfected with a mutated IkappaBalpha (IkappaBalphaM), which blocks NF-kappaB activity. Parental (PC-3M), control vector-transfected (PC-3M-Neo), and IkappaBalphaM-transfected (PC-3M-IkappaBalphaM) cells were injected into the prostate gland of nude mice. PC-3M and PC-3M-Neo cells produced rapidly growing tumors and regional lymph node metastasis, whereas PC-3M-IkappaBalphaM cells produced slow growing tumors with low metastatic potential. NF-kappaB signaling blockade significantly inhibited in vitro and in vivo expression of three major proangiogenic molecules, VEGF, IL-8, and MMP-9, and hence decreased neoplastic angiogenesis. Inhibition of NF-kappaB activity in PC-3M cells also resulted in the downregulation of MMP-9 mRNA and collagenase activity, resulting in decreased invasion through Matrigel. Collectively, these data suggest that blockade of NF-kappaB activity in PC-3M cells inhibits angiogenesis, invasion, and metastasis.

Patterned deposition of cells and proteins onto surfaces by using three-dimensional microfluidic systems

Three-dimensional microfluidic systems were fabricated and used to pattern proteins and mammalian cells on a planar substrate. The three-dimensional topology of the microfluidic network in the stamp makes this technique a versatile one with which to pattern multiple types of proteins and cells in complex, discontinuous structures on a surface. The channel structure, formed by the stamp when it is in contact with the surface of the substrate, limits migration and growth of cells in the channels. With the channel structure in contact with the surface, the cells stop dividing once they form a confluent layer. Removal of the stamp permits the cells to spread and divide.

Oral cancer risk in relation to sexual history and evidence of human papillomavirus infection

BACKGROUND

Experimental models and analyses of human tumors suggest that oncogenic, sexually transmittable human papillomaviruses (HPVs) are etiologic factors in the development of oral squamous cell carcinoma (SCC). We conducted a population-based, case-control study to determine whether the risk of this cancer is related to HPV infection and sexual history factors.

METHODS

Case subjects (n = 284) were 18-65-year-old residents of three counties in western Washington State who were newly diagnosed with oral SCC from 1990 through 1995. Control subjects (n = 477) similar in age and sex were selected from the general population. Serum samples were tested for HPV type 16 capsid antibodies. Exfoliated oral tissue collected from case and control subjects and tumor tissue from case subjects were tested for HPV DNA. Odds ratios (ORs) were calculated after adjusting for age, sex, cigarette smoking, and alcohol consumption.

RESULTS

Among males only, oral SCC risk increased with self-reported decreasing age at first intercourse, increasing number of sex partners, and a history of genital warts. Approximately 26% of the tumors in case subjects contained HPV DNA; 16.5% of the tumors contained HPV type 16 DNA. The prevalence of oncogenic HPV types in exfoliated oral tissue was similar in case and control subjects. The ORs for HPV type 16 capsid seropositivity were 2.3 (95% confidence interval [CI] = 1.6-3.3) for all oral SCCs and 6.8 (95% CI = 3.0-15.2) for oral SCCs containing HPV type 16 DNA. The joint association of cigarette smoking and HPV type 16 capsid seropositivity with oral SCC (OR = 8.5; 95% CI = 5.1-14.4) was stronger than predicted from the sum of individual associations with current smoking (OR = 3.2; 95% CI = 2.0-5.2) and seropositivity (OR = 1.7; 95% CI = 1.1-2.6).

CONCLUSIONS

HPV type 16 infection may contribute to the development of a small proportion of oral SCCs in this population, most likely in combination with cigarette smoking.

How stable is stable? Function versus community composition

The microbial community dynamics of a functionally stable, well-mixed, methanogenic reactor fed with glucose were analyzed over a 605-day period. The reactor maintained constant pH and chemical oxygen demand removal during this period. Thirty-six rrn clones from each of seven sampling events were analyzed by amplified ribosomal DNA restriction analysis (ARDRA) for the Bacteria and Archaea domains and by sequence analysis of dominant members of the community. Operational taxonomic units (OTUs), distinguished as unique ARDRA patterns, showed reproducible distribution for three sample replicates. The highest diversity was observed in the Bacteria domain. The 16S ribosomal DNA Bacteria clone library contained 75 OTUs, with the dominant OTU accounting for 13% of the total clones, but just 21 Archaea OTUs were found, and the most prominent OTU represented 50% of the clones from the respective library. Succession in methanogenic populations was observed, and two periods were distinguished: in the first, Methanobacterium formicicum was dominant, and in the second, Methanosarcina mazei and a Methanobacterium bryantii-related organism were dominant. Higher variability in Bacteria populations was detected, and the temporal OTU distribution suggested a chaotic pattern. Although dominant OTUs were constantly replaced from one sampling point to the next, phylogenetic analysis indicated that inferred physiologic changes in the community were not as dramatic as were genetic changes. Seven of eight dominant OTUs during the first period clustered with the spirochete group, although a cyclic pattern of substitution occurred among members within this order. A more flexible community structure characterized the second period, since a sequential replacement of a Eubacterium-related organism by an unrelated deep-branched organism and finally by a Propionibacterium-like species was observed. Metabolic differences among the dominant fermenters detected suggest that changes in carbon and electron flow occurred during the stable performance and indicate that an extremely dynamic community can maintain a stable ecosystem function.

Aberrant FoxM1B expression increases matrix metalloproteinase-2 transcription and enhances the invasion of glioma cells

We recently showed that FoxM1 is overexpressed in human glioblastomas and that forced FoxM1B expression in anaplastic astrocytoma cells leads to the formation of highly invasive glioblastoma multiforme (GBM) in nude mice. However, the molecular mechanisms by which FoxM1 enhances glioma invasion are unknown. In this study, we found that FoxM1 overexpression increased matrix metalloproteinase (MMP)-2 expression in glioma cells, whereas blockade of FoxM1 expression suppressed MMP-2 expression. Transfection of FoxM1 into glioma cells directly activated the MMP-2 promoter, whereas inhibition of FoxM1 expression by FoxM1-siRNA suppressed its activation. We identified a FoxM1-binding site in the MMP-2 promoter and demonstrated that FoxM1 protein bound directly to it. Mutation of this FoxM1-binding site significantly attenuated MMP-2 promoter activity. Furthermore, FoxM1 overexpression increased the invasiveness of glioma cells, whereas inhibition of FoxM1 expression suppressed the invasiveness of GBM cells. Inhibition of MMP-2 by a specific MMP-2 inhibitor reversed the invasive phenotype of glioma cells overexpressing FoxM1. Finally, immunohistochemical analysis of 45 human GBM specimens showed a significant correlation between FoxM1 overexpression and elevated MMP-2 expression. Collectively, these findings provide evidence that FoxM1 contributes to glioma progression by enhancing MMP-2 gene transcription and thus tumor-cell invasion.

TAL nucleases (TALNs): hybrid proteins composed of TAL effectors and FokI DNA-cleavage domain

DNA double-strand breaks enhance homologous recombination in cells and have been exploited for targeted genome editing through use of engineered endonucleases. Here we report the creation and initial characterization of a group of rare-cutting, site-specific DNA nucleases produced by fusion of the restriction enzyme FokI endonuclease domain (FN) with the high-specificity DNA-binding domains of AvrXa7 and PthXo1. AvrXa7 and PthXo1 are members of the transcription activator-like (TAL) effector family whose central repeat units dictate target DNA recognition and can be modularly constructed to create novel DNA specificity. The hybrid FN-AvrXa7, AvrXa7-FN and PthXo1-FN proteins retain both recognition specificity for their target DNA (a 26 bp sequence for AvrXa7 and 24 bp for PthXo1) and the double-stranded DNA cleaving activity of FokI and, thus, are called TAL nucleases (TALNs). With all three TALNs, DNA is cleaved adjacent to the TAL-binding site under optimal conditions in vitro. When expressed in yeast, the TALNs promote DNA homologous recombination of a LacZ gene containing paired AvrXa7 or asymmetric AvrXa7/PthXo1 target sequences. Our results demonstrate the feasibility of creating a tool box of novel TALNs with potential for targeted genome modification in organisms lacking facile mechanisms for targeted gene knockout and homologous recombination.

Kruppel-like factor 4 (KLF4) is required for maintenance of breast cancer stem cells and for cell migration and invasion

Kruppel-like factor 4 (KLF4) is highly expressed in more than 70% of breast cancers and functions as an oncogene. However, an exact mechanism by which KLF4 enhances tumorigenesis of breast cancer remains unknown. In this study, we show that KLF4 was highly expressed in cancer stem cell (CSC)-enriched populations in mouse primary mammary tumor and breast cancer cell lines. Knockdown of KLF4 in breast cancer cells (MCF-7 and MDA-MB-231) decreased the proportion of stem/progenitor cells as demonstrated by expression of stem cell surface markers such as aldehyde dehydrogenase 1 (ALDH1), side-population (SP), and by in vitro mammosphere assay. Consistently KLF4 overexpression led to an increase of the cancer stem cell population. KLF4 knockdown also suppressed cell migration and invasion in MCF-7 and MDA-MB-231 cells. Furthermore, knockdown of KLF4 reduced colony formation in vitro and inhibited tumorigenesis in immunocompromised NOD/SCID mice, supporting an oncogenic role for KLF4 in breast cancer development. Further mechanistic studies revealed that the Notch signaling pathway was required for KLF4-mediated cell migration and invasion, but not for CSC maintenance. Taken together, our study provides evidence that KLF4 plays a potent oncogenic role in mammary tumorigenesis likely by maintaining stem cell-like features and by promoting cell migration and invasion. Thus, targeting KLF4 may provide an effective therapeutic approach to suppress tumorigenicity in breast cancer.

Control of cyclin D1, p27(Kip1), and cell cycle progression in human capillary endothelial cells by cell shape and cytoskeletal tension

The extracellular matrix (ECM) plays an essential role in the regulation of cell proliferation during angiogenesis. Cell adhesion to ECM is mediated by binding of cell surface integrin receptors, which both activate intracellular signaling cascades and mediate tension-dependent changes in cell shape and cytoskeletal structure. Although the growth control field has focused on early integrin and growth factor signaling events, recent studies suggest that cell shape may play an equally critical role in control of cell cycle progression. Studies were carried out to determine when cell shape exerts its regulatory effects during the cell cycle and to analyze the molecular basis for shape-dependent growth control. The shape of human capillary endothelial cells was controlled by culturing cells on microfabricated substrates containing ECM-coated adhesive islands with defined shape and size on the micrometer scale or on plastic dishes coated with defined ECM molecular coating densities. Cells that were prevented from spreading in medium containing soluble growth factors exhibited normal activation of the mitogen-activated kinase (erk1/erk2) growth signaling pathway. However, in contrast to spread cells, these cells failed to progress through G1 and enter S phase. This shape-dependent block in cell cycle progression correlated with a failure to increase cyclin D1 protein levels, down-regulate the cell cycle inhibitor p27(Kip1), and phosphorylate the retinoblastoma protein in late G1. A similar block in cell cycle progression was induced before this same shape-sensitive restriction point by disrupting the actin network using cytochalasin or by inhibiting cytoskeletal tension generation using an inhibitor of actomyosin interactions. In contrast, neither modifications of cell shape, cytoskeletal structure, nor mechanical tension had any effect on S phase entry when added at later times. These findings demonstrate that although early growth factor and integrin signaling events are required for growth, they alone are not sufficient. Subsequent cell cycle progression and, hence, cell proliferation are controlled by tension-dependent changes in cell shape and cytoskeletal structure that act by subjugating the molecular machinery that regulates the G1/S transition.

Bmk1/Erk5 is required for cell proliferation induced by epidermal growth factor

Epidermal growth factor (EGF) induces cell proliferation in a variety of cell types by binding to a prototype transmembrane tyrosine kinase receptor. Ligation of this receptor by EGF activates Erk1 and Erk2, members of the mitogen-activated protein (MAP) kinase family, through a Ras-dependent signal transduction pathway. Despite our detailed understanding of these events, the exact mechanism by which EGF causes cells to proliferate is unclear. Big MAP kinase (Bmk1), also known as Erk5, is a member of the MAP kinase family that is activated in cells in response to oxidative stress, hyperosmolarity and treatment with serum. Here we show that EGF is a potent activator of Bmk1. In contrast to Erk1/2, EGF-mediated activation of Bmk1 occurs independently of Ras and requires the MAP-kinase kinase Mek5. Expression of a dominant-negative form of Bmk1 blocks EGF-induced cell proliferation and prevents cells from entering the S phase of the cell cycle. These results demonstrate that Bmk1 is part of a distinct MAP-kinase signalling pathway that is required for EGF-induced cell proliferation and progression through the cell cycle.

Modularly assembled designer TAL effector nucleases for targeted gene knockout and gene replacement in eukaryotes

Recent studies indicate that the DNA recognition domain of transcription activator-like (TAL) effectors can be combined with the nuclease domain of FokI restriction enzyme to produce TAL effector nucleases (TALENs) that, in pairs, bind adjacent DNA target sites and produce double-strand breaks between the target sequences, stimulating non-homologous end-joining and homologous recombination. Here, we exploit the four prevalent TAL repeats and their DNA recognition cipher to develop a 'modular assembly' method for rapid production of designer TALENs (dTALENs) that recognize unique DNA sequence up to 23 bases in any gene. We have used this approach to engineer 10 dTALENs to target specific loci in native yeast chromosomal genes. All dTALENs produced high rates of site-specific gene disruptions and created strains with expected mutant phenotypes. Moreover, dTALENs stimulated high rates (up to 34%) of gene replacement by homologous recombination. Finally, dTALENs caused no detectable cytotoxicity and minimal levels of undesired genetic mutations in the treated yeast strains. These studies expand the realm of verified TALEN activity from cultured human cells to an intact eukaryotic organism and suggest that low-cost, highly dependable dTALENs can assume a significant role for gene modifications of value in human and animal health, agriculture and industry.

Rice xa13 recessive resistance to bacterial blight is defeated by induction of the disease susceptibility gene Os-11N3

The rice (Oryza sativa) gene xa13 is a recessive resistance allele of Os-8N3, a member of the NODULIN3 (N3) gene family, located on rice chromosome 8. Os-8N3 is a susceptibility (S) gene for Xanthomonas oryzae pv oryzae, the causal agent of bacterial blight, and the recessive allele is defeated by strains of the pathogen producing any one of the type III effectors AvrXa7, PthXo2, or PthXo3, which are all members of the transcription activator-like (TAL) effector family. Both AvrXa7 and PthXo3 induce the expression of a second member of the N3 gene family, here named Os-11N3. Insertional mutagenesis or RNA-mediated silencing of Os-11N3 resulted in plants with loss of susceptibility specifically to strains of X. oryzae pv oryzae dependent on AvrXa7 or PthXo3 for virulence. We further show that AvrXa7 drives expression of Os-11N3 and that AvrXa7 interacts and binds specifically to an effector binding element within the Os-11N3 promoter, lending support to the predictive models for TAL effector binding specificity. The result indicates that variations in the TAL effector repetitive domains are driven by selection to overcome both dominant and recessive forms of resistance to bacterial blight in rice. The finding that Os-8N3 and Os-11N3 encode closely related proteins also provides evidence that N3 proteins have a specific function in facilitating bacterial blight disease.

Multiple microRNAs modulate p21Cip1/Waf1 expression by directly targeting its 3' untranslated region

Cyclin-dependent kinase inhibitor 1A (CDKN1A), also known as p21Cip1/Waf1, is a master downstream effector of tumor suppressors. In this study, we experimentally demonstrate through a high-throughput luciferase reporter screen that p21Cip1/Waf1 can be directly targeted by nearly 28 microRNAs (miRNAs). The results were further confirmed by a series of mutational analyses and luciferase reporter assays. These 28 miRNAs can substantially inhibit p21Cip1/Waf1 expression, predominantly at translational level. Many of these miRNAs were upregulated in cancers and might serve as modulators of oncogenesis. Furthermore, 8 of these 28 p21-regulating miRNAs are located in the chromosome 19 miRNA cluster, the largest miRNA gene cluster in humans, and they can clearly promote cell proliferation and cell-cycle progression in choriocarcinoma cells. In conclusion, our screening strategy provides an alternative approach to uncovering miRNA modulators of an individual mRNA, and it has identified multiple miRNAs that can suppress p21Cip1/Waf1 expression by directly targeting its 3' untranslated region.

Antiviral defense in mice lacking both alpha/beta and gamma interferon receptors

Alpha/beta interferon (IFN) and gamma IFN exert widely overlapping biological effects. Still, mice with individually inactivated alpha/beta or gamma receptors exhibit variably severely reduced resistance to infection and altered immune responses. To investigate to what extent the two IFN systems are functionally redundant, we generated mice with a combined receptor defect (AG129 mice). Like mice with individual mutations, AG129 mice had no apparent anomalies, confirming that in the mouse the IFN system is not essential for normal development. These mice showed an additive phenotype with respect to antiviral defense and exhibited an increased susceptibility to lymphocytic choriomeningitis virus (LCMV) and notably vaccinia virus infection. Because of unlimited replication and subsequent rapid exhaustion of cytotoxic T lymphocyte (CTL) precursors, these mice were unable to mount a CTL response to LCMV. CD8(+)-mediated immunopathology was absent in LCMV-infected mice, and virus persisted. Vaccinia virus replicated much faster in AG129 mice, and a 10(4)-fold lower dose of vaccinia virus was sufficient to prime these mice. With the normal priming dose of 10(6) PFU, cytopathic effects and overwhelming infection possibly causing partial exhaustion of CTL interfered with the anti-vaccinia virus response. Even though global antiviral immunoglobulin G (IgG) titers were within normal ranges, the IgG subclass distribution was heavily biased toward IgG1.