Apparent Arrest Research Articles

Effect of temperature on apparent crack arrest toughness of Eurofer97 measured by a newly developed small specimen test technique

Neutron embrittlement of in-core and out-of-core components made of ferritic steels is one of the key parameters limiting the life of power plants. Owing to the small volume of available irradiation facilities and the limited number of neutron-irradiated specimens, techniques to measure initiation fracture toughness with small specimens have been developed over the years. Although arrest toughness is of equal importance regarding safety assessment, the emphasis has been put on the effect of specimen size on initiation toughness and only a few small specimen test techniques can be found for arrest toughness measurements. The objective of the current work was to develop an experimental technique for measuring the apparent arrest toughness of ferritic steels with miniaturized specimens. Small cantilevers made of the 9Cr Eurofer97 equiaxed ferritic steel were produced with a brittle thin laser-treated layer, which enables crack initiation. The cracks were successfully arrested in the more ductile equiaxed ferritic matrix in a series of tests that were carried out from -123 °C to room temperature with different test configurations. The mechanical tests showed that brittle fracture could be triggered and stopped inside the specimen with a width of 2 mm over a temperature range of more than 100 °C. An apparent arrest toughness was calculated and its temperature dependence was related to the plastic work dissipated by a propagating crack.

Megathrust reflectivity reveals the updip limit of the 2014 Iquique earthquake rupture

The updip limit of seismic rupture during a megathrust earthquake exerts a major control on the size of the resulting tsunami. Offshore Northern Chile, the 2014 Mw 8.1 Iquique earthquake ruptured the plate boundary between 19.5° and 21°S. Rupture terminated under the mid-continental slope and did not propagate updip to the trench. Here, we use state-of-the-art seismic reflection data to investigate the tectonic setting associated with the apparent updip arrest of rupture propagation at 15 km depth during the Iquique earthquake. We document a spatial correspondence between the rupture area and the seismic reflectivity of the plate boundary. North and updip of the rupture area, a coherent, highly reflective plate boundary indicates excess fluid pressure, which may prevent the accumulation of elastic strain. In contrast, the rupture area is characterized by the absence of plate boundary reflectivity, which suggests low fluid pressure that results in stress accumulation and thus controls the extent of earthquake rupture. Generalizing these results, seismic reflection data can provide insights into the physical state of the shallow plate boundary and help to assess the potential for future shallow rupture in the absence of direct measurements of interplate deformation from most outermost forearc slopes.

DISSEMINATED METASTATIC MELANOMA OF UNKNOWN ORIGIN fiRST DIAGNOSED IN THE ORAL CAVITY WITH NEAR RESOLUTION AFTER IMMUNOTHERAPY AND SUBSEQUENT IMMUNE-RELATED SEQUALAE

Herein, we report an atypical clinicopathological presentation of amelanotic melanoma first diagnosed in the oral cavity of a 68-year-old man. The tumor was immunopositive for HMB45 and S-100, and weakly positive to Melan A. PET (positron emission tomography) and CT (computed tomography) scans demonstrated widespread organ and bone metastases, obviating surgical intervention. Standard immunotherapy was instituted with ipilimumab and nivolumab. At 3-weeks, near resolution of the oral lesion was evident and repeat imaging showed resolution of the left lung lesions and marked reductions in size of other affected sites. The patient subsequently experienced and recovered from multiple immune-related adverse events, including autoimmune carditis, which was managed with steroid administration. Following subsequent immunoregimens and 4 months since the initial diagnosis, the patient succumbed to sudden apparent cardiac arrest. Historically, surgery, chemotherapy, and radiotherapy to manage mucosal melanoma have yielded poor long-term outcomes, necessitating alternative efforts to improve patient care. Immunotherapy is an emerging modality for management of late-stage melanoma and has shown promising results to extend overall survival.

Effects of cold storage on quality of Chrysopa pallens and recovery of fecundity by insulin

The green lacewing, Chrysopa pallens Wesmael, is one of the most beneficial and prolific insects found in many horticultural and agricultural cropping system. Here, the effects of low temperature storage on quality of C. pallens were investigated by storing cocoons at 10 °C for different days. Results revealed, after removal from cold storage, emergence rate declined gradually as storage duration increased. After storage of 20 days, the emergence rate in cold-stored group is about 62.8% of that in unstored group. After eclosion, lifetime fecundity, preemergence period, oviposition period and longevity of adults in cold-stored group showed curves similar to emergence rate. However, preoviposition period and egg hatchability were not significantly affected by cold. After being stored for 20 days, the total fecundity of females emerging from cold-stored cocoons was about 64.5% of that of females emerging from unstored cocoons. Six days post emergence, females in cold-stored group showed apparent arrest of ovarian development and significant reductions of protease, lipase and trehalase activities when compared to unstored controls. When bovine insulin was exogenously used, the females emerging from cold-stored cocoons dramatically restored ovarian development and reproductive capacity. These results suggested that C. pallens pupae are suitable for cold storage and insulin hormone can be used as reproduction stimuli in this predatory species after cold storage.

Induction of p53-independent growth inhibition in lung carcinoma cell A549 by gypenosides.

The objectives of this study are to investigate antiproliferative effect and mechanisms of bioactive compounds from Gynostemma pentaphyllum (G. pentaphyllum) on lung carcinoma cell A549. Saponins, carotenoids and chlorophylls were extracted and fractionated by column chromatography, and were subjected to high-performance liquid chromatography-mass spectrometry analyses. The saponin fraction, which consisted mainly of gypenoside (Gyp) XXII and XXIII, rather than the carotenoid and chlorophyll ones, was effective in inhibiting A549 cell growth in a concentration- and a time-dependent manner as evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The estimated half maximal inhibitory concentration (IC50) of Gyp on A549 cells was 30.6 μg/ml. Gyp was further demonstrated to induce an apparent arrest of the A549 cell cycle at both the S phase and the G2/M phase, accompanied by a concentration- and a time-dependent increase in the proportions of both the early and late apoptotic cells. Furthermore, Gyp down-regulated cellular expression of cyclin A and B as well as BCL-2, while up-regulated the expression of BAX, DNA degradation factor 35 KD, poly [ADP-ribose] polymerase 1, p53, p21 and caspase-3. Nevertheless, both the treatment of a p53 inhibitor, pifithrin-α, and the small hairpin RNA-mediated p53 knockdown in the A549 cells did not alter the growth inhibition effect induced by Gyp. As a result, the cell cycle arrest and apoptosis of A549 cells induced by Gyp would most likely proceed through p53-independent pathway(s).

ZNF750 Is Expressed in Differentiated Keratinocytes and Regulates Epidermal Late Differentiation Genes

Disrupted skin barrier due to altered keratinocyte differentiation is common in pathologic conditions such as atopic dermatitis, ichthyosis and psoriasis. However, the molecular cascades governing keratinocyte terminal differentiation are poorly understood. We have previously demonstrated that a dominant mutation in ZNF750 leads to a clinical phenotype reminiscent of psoriasis and seborrheic dermatitis. Here we show that ZNF750 is a nuclear protein bearing a functional C-terminal nuclear localization signal. ZNF750 was specifically expressed in the epidermal suprabasal layers and its expression was augmented during differentiation, both in human skin and in-vitro, peaking in the granular layer. Silencing of ZNF750 in Ca2+-induced HaCaT keratinocytes led to morphologically apparent arrest in the progression of late differentiation, as well as diminished apoptosis and sustained proliferation. ZNF750 knockdown cells presented with markedly reduced expression of epidermal late differentiation markers, including gene subsets of epidermal differentiation complex and skin barrier formation such as FLG, LOR, SPINK5, ALOX12B and DSG1, known to be mutated in various human skin diseases. Furthermore, overexpression of ZNF750 in undifferentiated cells induced terminal differentiation genes. Thus, ZNF750 is a regulator of keratinocyte terminal differentiation and with its downstream targets can serve in future elucidation of therapeutics for common diseases of skin barrier.

Antitumor activities of dFv-LDP-AE: An enediyne-energized fusion protein targeting tumor-associated antigen gelatinases

Gelatinases play an important role in tumor growth and metastasis, and overexpression of these molecules is strongly correlated with poor prognosis in a variety of malignant tumors. Lidamycin is an enediyne antitumor antibiotic with potent cytotoxicity. We previously reported that a tandem scFv format (dFv-LDP-AE) showed enhanced binding ability with gelatinases compared with the scFv-lidamycin conjugate (Fv-LDP-AE). In this study, the antitumor activities of dFv-LDP-AE on hepatocellular carcinoma (HCC) were evaluated invitro and invivo. By SDS-PAGE analysis, it was found that partial fusion protein dFv-LDP existed as dimer; the results of ELISA and immunofluorescence demonstrated that the fusion protein dFv-LDP could efficiently bind to hepatoma cells invitro. The apparent arrest of cell cycle at G2/M phase and induction of apoptosis at nanomole levels indicated that the dFv-LDP-AE was very potent against HCC. In invivo experiments, dFv-LDP-AE shown enhanced cytotoxic effects compared to those of LDM. Administration at mouse tolerable dosage level, the inhibition rate of tumor growth was 89.5% of dFv-LDP-AE vs. 73.6% of LDM on transplantable H22 in mice (P<0.05) and, 87.3% of dFv-LDP-AE vs. 63.4% of LDM on hepatoma Bel-7402 in athymic mice (P<0.01). Small animal optical imaging showed that the FITC-labeled dFv-LDP preferentially localized in the tumor site in less than 30min, which demonstrated remarkable tumor-targeting properties. Taken together with the above findings, the enediyne-energized fusion protein dFv-LDP-AE showed potential application as a new agent for therapeutic appications in HCC.

The simplicity of males: Dwarf males of four species of Osedax (Siboglinidae; Annelida) investigated by confocal laser scanning microscopy

Dwarf males of the bone-eating worms Osedax (Siboglinidae, Annelida) have been proposed to develop from larvae that settle on females rather than on bone. The apparent arrest in somatic development and resemblance of the males to trochophore larvae has been posited as an example of paedomorphosis. Here, we present the first investigation of the entire muscle and nervous system in dwarf males of Osedax frankpressi, O. roseus, O. rubiplumus, and O. "spiral" analyzed by multistaining and confocal laser scanning microscopy. Sperm shape and spermiogenesis, the sperm duct and internal and external ciliary patterns were likewise visualized. The males of all four species possess morphological traits typical of newly settled siboglinid larvae: a prostomium, a peristomium with a prototroch, one elongate segment and a second shorter segment. Each segment has a ring of eight long-handled hooked chaetae. The longitudinal muscles are distributed as evenly spaced strands forming a grid with the thin outer circular muscles. Oblique protractor and retractor muscles are associated with each of the chaetal sacs. The nervous system comprises a cerebral ganglion, a prototroch nerve ring, paired dorsolateral longitudinal nerves, five ventral longitudinal nerves with paired, posterior ganglia and a terminal commissure, as well as a net of fine peripheral transverse plexuses surrounding the first segment. Internal ciliation occurs as paired ventrolateral bands along the first segment. The bands appear to lead the free mature sperm to a ciliated duct and seminal vesicle lying just behind the prototroch region. A duct then runs from the seminal vesicle into the dorsal part of the prostomium. The similarity of Osedax males to the larvae of Osedax and other siboglinid annelids as well as similarities shown here to the neuromuscular organization seen in other annelid larvae supports the hypothesis of paedomorphosis in males of Osedax.

Jean Sebastian Yolton (1924-2008)

&#x0D; &#x0D; &#x0D; Born in Cincinnati, Ohio on 22 March 1924, Jean S. Yolton, librarian, bibliographer, scholar, cordon bleu cook, and widow of John W. Yolton, died of apparent cardiac arrest in her Piscataway, New Jersey home on 15 January 2008. She is survived by two daughters and two granddaughters.&#x0D; &#x0D; &#x0D;

What is your diagnosis? Pancytopenia in a dog

A 4-year-old male, castrated, mixed-breed dog was presented to the Colorado State University Veterinary Teaching Hospital with a 1-week history of polyuria, polydipsia, lethargy, fever, inappetence, weight loss, and soft mucoid stool. The dog was depressed and had pale, icteric mucous membranes. Results of a CBC included normocytic, normochromic, nonregenerative anemia, neutropenia, and thrombocytopenia, with 43% blast cells (200/microL), many of which contained fine azurophilic granules. Cytologic evaluation of the bone marrow aspirates revealed mild granulocytic hyperplasia that appeared to be left-shifted in an apparent maturation arrest. A large population of blast cells comprised 35% of nucleated cells; the blasts had high nuclear to cytoplasmic ratios, deeply basophilic cytoplasm with vacuoles, and prominent nucleoli. Most cells also contained many fine azurophilic granules clustered in the paranuclear region. At necropsy, neoplastic cells were abundant in the bone marrow. Immunohistochemically the cells expressed CD3epsilon, and an oligoclonal T-cell rearrangement was found. The diagnosis was proliferative disorder of CD3(+) granular lymphocytes, with associated pancytopenia. Because the blast cells were morphologically similar to myeloblasts and immunohistochemistry was required to confirm the diagnosis, T-cell lymphoproliferative disease should be considered in dogs with pancytopenia presenting with similar clinical features.

Ising model with memory: coarsening and persistence properties

We consider the coarsening properties of a kinetic Ising model with a memory field. Theprobability of a spin-flip depends on the persistence time of the spin in a state. The more aspin has been in a given state, the less the spin-flip probability is. We numerically studiedthe growth and persistence properties of such a system on a two-dimensional square lattice.The memory introduces energy barriers which freeze the system at zero temperature. Atfinite temperature we can observe an apparent arrest of coarsening for low temperature andlong memory length. However, since the energy barriers introduced by memory are due tolocal effects, there exists a timescale on which coarsening takes place as for the Isingmodel. Moreover the two-point correlation functions of the Ising model with andwithout memory are the same, indicating that they belong to the same universalityclass.

Distribution, Organization, and Ecology of Bacteria in Chronic Wounds

Between 1 and 2% of the population in the developed world experiences a nonhealing or chronic wound characterized by an apparent arrest in a stage dominated by inflammatory processes. Lately, research groups have proposed that bacteria might be involved in and contribute to the lack of healing of these wounds. To investigate this, we collected and examined samples from chronic wounds obtained from 22 different patients, all selected because of suspicion of Pseudomonas aeruginosa colonization. These wound samples were investigated by standard culturing methods and peptide nucleic acid-based fluorescence in situ hybridization (PNA FISH) for direct identification of bacteria. By means of the culturing methods, Staphylococcus aureus was detected in the majority of the wounds, whereas P. aeruginosa was observed less frequently. In contrast, using PNA FISH, we found that a large fraction of the wounds contained P. aeruginosa. Furthermore, PNA FISH revealed the structural organization of bacteria in the samples. It appeared that P. aeruginosa aggregated as microcolonies imbedded in the matrix component alginate, which is a characteristic hallmark of the biofilm mode of growth. The present investigation suggests that bacteria present within these wounds tend to be aggregated in microcolonies imbedded in a self-produced matrix, characteristic of the biofilm mode of growth. Additionally, we must conclude that there exists no good correlation between bacteria detected by standard culturing methods and those detected by direct detection methods such as PNA FISH. This strongly supports the development of new diagnostic and treatment strategies for chronic wounds.

Anaesthesia and high altitude: a history

During an expedition to climb Everest in 1933, expedition doctor Raymond Greene administered an open-drop chloroform anaesthetic to a Tibetan patient at an altitude of more than 14,000 feet. The patient's subsequent apparent cardiopulmonary arrest has long been attributed to the effects of altitude on anaesthetic delivery. However, anaesthetics can be safely administered at a wide variety of altitudes by adequately trained and experienced anaesthetists. The problems may have arisen from an inadequate depth of anaesthesia consequent to decreased chloroform vaporisation in a cold environment, Greene's concern about potential depression of ventilation and the contemporary lack of a precise approach to assessing depth of anaesthesia.

Primarily non-surgical management of osteomyelitis of the foot in diabetes

We examined the use of surgery and assessed the response to non-surgical management of osteomyelitis of the foot in diabetic patients. We reviewed the records of all patients presenting to a single specialist centre with osteomyelitis complicating a diabetic foot ulcer over a 5 year period. Details were extracted on antibiotic choice and treatment duration, hospital admission, incidence of minor and major amputation, and 12 month outcomes. There were 147 patients, with mean age 64.7 years (66% men). Of these, 26 (18%) were admitted to hospital at the time of presentation and managed with intravenous antibiotics; the remainder were managed with oral antibiotics as outpatients. Surgery was undertaken because of life- or limb-threatening infection, or failure to respond, in 34 (23%) patients (minor amputation 28, major amputation six patients). The remaining 113 were managed non-surgically. Remission was induced in 66 (58.4% of 113), while 35 (31%) had a relapse. Of those experiencing relapse, 27 (77%) achieved apparent arrest of the infection with a further course of antibiotics; six underwent minor and two underwent major amputation. Of all 113 whose infection was initially managed without surgery, apparent remission was achieved with antibiotics alone in 93 (82.3%). As these observations were made in an unselected case series, they give more insight into the respective roles of surgical and non-surgical management. The results confirm that although urgent surgery is indicated in some patients, non-surgical management of those without limb-threatening infection is associated with a high rate of apparent remission.

Quaternary temporal stability of a regional strike-slip and rift fault intersection

Intersecting strike-slip and normal fault systems form either two or three plate configurations. In circumstances where they intersect to form a triple junction, internal block deformation produces a quasi-stable 3-D configuration permitting maintenance of both the regional geometry and kinematics of the intersection. This paper examines the temporal stability of such a triple junction in New Zealand over a range of timescales, from individual earthquakes to millions of years, and discusses the factors that impact its stability. Using seismic-reflection, gravity, drill-hole and outcrop data, the accumulation of vertical displacements is examined, both on individual faults and across the intersection zone between the strike-slip North Island Fault System (NIFS) and the Taupo Rift. Fault-throws and throw rates for the NIFS and Taupo Rift suggest that despite a three-fold increase in throw rates in both fault systems at about 0.3 Ma, which may have modified the orientation of the slip vectors and therefore the contemporary kinematics of the triple junction, the intersection of the two fault systems has functioned coherently for the last 0.6–1.5 Myr accumulating vertical displacements interdependently since the early stages of rifting. The apparent arrest of a large magnitude earthquake on the rift-bounding fault adjacent to the intersection, suggests that the short-term dynamic behaviour of the system is relatively complex compared to the more coherent long-term kinematics.

The nucleolar protein SURF-6 is essential for viability in mouse NIH/3T3 cells

SURF-6 is a bona fide nucleolar protein comprising an evolutionary conserved family that extends from human to yeast. The expression of the mammalian SURF-6 has been recently found to be regulated during the cell cycle. In order to determine the importance of SURF-6 in mammalian cells, we applied the Tet-On system to regulate conditionally, in response to tetracycline, the expression of an antisense RNA (asRNA) that targets Surf-6 mRNA in mouse NIH/3T3 cells. Induced Surf-6 asRNA caused an effective depletion of SURF-6 protein resulted in cell death and in an apparent arrest in the G1 phase of the cell cycle. These results provide for the first time evidence that expression of SURF-6 is essential for mammalian cell viability, and suggest that SURF-6 might participate in the progression of cell cycle.

An Aurora Kinase Homologue Is Involved in Regulating Both Mitosis and Cytokinesis in Trypanosoma brucei

The chromosomal passenger protein aurora kinases have been implicated in regulating chromosome segregation and cell division. Three aurora kinase homologues were identified (TbAUK1, -2 and -3) in the Trypanosome Genomic Data Base, and their expressions in the procyclic form of Trypanosoma brucei were knocked down individually by using the RNA interference technique. Only a knockdown of TbAUK1 arrested the cells in G(2)/M phase with each cell showing an extended posterior end, two kinetoplasts, and an enlarged nucleus, apparently the result of an inhibited kinetoplast multiplication and a failed mitosis. There is no mitotic spindle structure in the TbAUK1-depleted cell. The two kinetoplasts moved apart from each other but stopped just before cytokinesis, suggesting that cytokinesis was blocked in its early phase. Overexpression of TbAUK1 in the cells resulted in little change in cell growth. By immunofluorescence, TbAUK1 was primarily localized to the nucleus in interphase and to the mitotic spindle during apparent metaphase and anaphase. Thus, differing from other eukaryotes, TbAUK1 has an apparent triple function in coupling mitosis and kinetoplast replication with cytokinesis in T. brucei. T. brucei polo-like kinase, previously identified as the initiator of cytokinesis without apparent involvement in mitosis in the trypanosome, was either depleted or overexpressed in the TbAUK1-deficient cells. A dominant TbAUK1-depleted phenotype was demonstrated in both cases, suggesting that TbAUK1 plays an essential role in cytokinesis that cannot be affected by changes in the level of T. brucei polo-like kinase. To our knowledge, this is the first time that the function of an aurora B-like kinase is a prerequisite for polo-like kinase action in initiating cytokinesis. TbAUK1 is also the first identified protein that couples both mitosis and kinetoplast replication with cytokinesis in the trypanosome.

Tet-Regulated Expression of Mutant Neutrophil Elastase in HL-60 Cells: A Cellular Model of Severe Congenital Neutropenia.

Severe congenital neutropenia (SCN) is an inheritable hematopoietic disorder characterized by extremely low level of circulating neutrophils, ineffective intramedulary hematopoiesis with “maturation arrest” at the promyelocytic stage of differentiation, recurrent severe infections, and evolution to acute myelogenous leukemia (AML). Accelerated apoptosis of bone marrow-derived myeloid progenitor cells and cell cycle arrest of CD34+ cells was reported in SCN patients. We also reported that heterozygous mutations in the neutrophil elastase (NE) gene have been identified in approximately 80% of SCN patients. Transient expression of mutant but not normal NE triggered accelerated apoptotic cell death of human promyelocytic HL-60 cells supporting the causative role of mutant NE in pathogenesis of SCN.Here we present cellular model of SCN based on newly established tet-off HL-60 human promyelocytic cell line with inducible doxycycline-regulated expression of mutant NE with 8-amino acid deletion identified in a patient evolved to develop AML. Induced expression of mutant elastase in tet-off HL-60 cells treated with DMSO led to a block of differentiation or “maturation arrest” at the promyelocytic stage of differentiation with a significantly reduced proportion of differentiated cells (approximately 20% vs 70% in control) and higher proportion (~40%) of primitive undifferentiated cells compared with control DMSO-treated HL-60 cells expressing only normal NE (~10%). Flow cytometry analysis of annexin V-labeled cells repeatedly revealed approximately 2-fold higher rate of apoptosis in tet-off HL-60 cells with induced expression of mutant NE compared with control cells.FACS analysis of DAPI-labeled tet-off HL-60 cells with induced expression of mutant NE revealed abnormal cell cycle progression with gradual accumulation and apparent arrest of cells in G1-phase of the cell cycle similar to that reported for SCN patients. Interestingly, the apoptotic cell shrinking and swelling as determined by flow cytometry was observed in all phases of the cell cycle suggesting that accelerated apoptosis rather than cell cycle arrest is the primary abnormality caused by expression of mutant NE, and the abnormal cell cycle progression is a consequence of this impaired cell survival. Further analysis revealed a dramatic reduction in mitochondrial membrane potential of tet-off HL-60 cells expressing mutant NE compared with control cells. The reduced mitochondrial membrane potential as determined by FACS was observed as early as 24 hours of induction of mutant NE expression and before the accelerated apoptosis or cell cycle arrest was detected. Western blot analysis demonstrated that caspase-3 was not activated in the cells even after 3 days of mutant NE induction. Further analysis of apoptosis regulators revealed a down-regulation of Bcl-2 expression and up-regulation of Bax in cells with induced expression of mutant elastase. These data suggest that mutant elastase-mediated “maturation arrest” of human promyelocytic cells in patients with SCN and SCN/AML is associated with reduced expression of anti-apoptotic Bcl-2 and upregulation of pro-apoptotic Bax proteins that trigger a dramatic reduction in mitochondrial membrane potential and subsequent caspase-independent apoptosis and cell cycle arrest. Current studies focused on elucidating and characterizing specific molecular interactions mediating the pro-apoptotic effect of mutant neutrophil elastase in SCN.

Plastid protein synthesis is required for plant development in tobacco.

Chloroplasts fulfill important functions in cellular metabolism. The majority of plastid genome-encoded genes is involved in either photosynthesis or chloroplast gene expression. Whether or not plastid genes also can determine extraplastidic functions has remained controversial. We demonstrate here an essential role of plastid protein synthesis in tobacco leaf development. By using chloroplast transformation, we have developed an experimental system that produces recombination-based knockouts of chloroplast translation in a cell-line-specific manner. The resulting plants are chimeric and, in the presence of translational inhibitors, exhibit severe developmental abnormalities. In the absence of active plastid protein synthesis, leaf blade development is abolished because of an apparent arrest of cell division. This effect appears to be cell-autonomous in that adjacent sectors of cells with translating plastids are phenotypically normal but cannot complement for the absence of plastid translation in mutant sectors. Developmental abnormalities also are seen in flower morphology, indicating that the defects are not caused by inhibited expression of plastid photosynthesis genes. Taken together, our data point to an unexpected essential role of plastid genes and gene expression in plant development and cell division.

Cytotoxic constituents of Aspergillus terreus from the rhizosphere of Opuntia versicolor of the Sonoran Desert.

A novel cyclopentenedione, asterredione (1), two new terrecyclic acid A derivatives, (+)-5(6)-dihydro-6-methoxyterrecyclic acid A (2) and (+)-5(6)-dihydro-6-hydroxyterrecyclic acid A (3), and five known compounds, (+)-terrecyclic acid A (4), (-)-quadrone (5), betulinan A (6), asterriquinone D (7), and asterriquinone C-1 (8), were isolated from Aspergillus terreus occurring in the rhizosphere of Opuntia versicolor, using bioassay-guided fractionation. Acid-catalyzed reaction of 2 under mild conditions afforded 4, whereas under harsh conditions 2 yielded 5 and (-)-isoquadrone (9). Catalytic hydrogenation and methylation of 4 afforded 5(6)-dihydro-terrecyclic acid A (10) and (+)-terrecyclic acid A methyl ester (11), respectively. The structures of 1-11 were elucidated by spectroscopic methods. All compounds were evaluated for cytotoxicity in a panel of three sentinel cancer cell lines, NCI-H460 (non-small cell lung cancer), MCF-7 (breast cancer), and SF-268 (CNS glioma), and were found to be moderately active. Cell cycle analysis of 2, 4, and 5 using the NCI-H460 cell line indicated that 4 is capable of disrupting the cell cycle through an apparent arrest to progression at the G(1) and G(2)/M phases in this p53 competent cell line. A pathway for the biosynthetic origin of asterredione (1) from asterriquinone D (7) is proposed.