HIV-1 Gag-RNA interaction occurs at a perinuclear/centrosomal site; analysis by confocal microscopy and FRET

The Gag polyprotein is the major structural protein of human immunodeficiency virus-1 (HIV-1) constituting the viral core. Between translation on cytoplasmic polysomes and assembly into viral particles at the plasma membrane, it specifically captures the RNA genome of the virus through binding RNA structural motifs (packaging signals -Psi) in the RNA. RNA is believed to be a structural facilitator of Gag assembly. Using a combined approach of immunofluorescence detection of Gag protein and in situ hybridisation detection of viral genomic RNA, we demonstrate that Gag protein colocalises early after expression with Psi+ RNA in the perinuclear region and also colocalises with centrioles. Colocalised RNA and protein subsequently traffic through the cytoplasm to the plasma membrane of the cell. Gag expressed from Psi- RNA diffuses throughout the cell. It is not found at centrioles and shows delayed cytoplasmic colocalisation with the RNA genome. RNA capture through Psi does not influence binding of Gag to microfilaments. Gag does not bind to tubulin during export. The presence of the packaging signal may coordinate capture of Psi+ RNA by Gag protein at the centrosome followed by their combined transport to the site of budding. HIV-1 Psi thus acts as a subcellular localisation signal as well as a high-affinity-binding site for Gag.     

Chromosome aberration and environmental physical activity: Down syndrome and solar and cosmic ray activity, Israel, 1990–2000

The possibility that environmental effects are associated with chromosome aberrations and various congenital pathologies has been discussed previously. Recent advances in the collection and computerization of data make studying these potential associations more feasible. The aim of this study was to investigate a possible link between the number of Down syndrome (DS) cases detected prenatally or at birth yearly in Israel over a 10-year period compared with the levels of solar and cosmic ray activity 1 year before the detection or birth of each affected child. Information about 1,108,449 births was collected for the years 1990–2000, excluding 1991, when data were unavailable. A total of 1,310 cases of DS were detected prenatally or at birth—138 in the non-Jewish community and 1,172 in the Jewish population. Solar activity indices—sunspot number and solar radio flux 2,800 MHz at 10.7 cm wavelength for 1989–1999—were compared with the number of DS cases detected. Pearson correlation coefficients (r) and their probabilities (P) were established for the percentage of DS cases in the whole population. There was a significant inverse correlation between the indices of solar activity and the number of cases of DS detected—r=–0.78, P=0.008 for sunspot number and r=–0.76, P=0.01 for solar flux. The possibility that cosmophysical factors inversely related to solar activity play a role in the pathogenesis of chromosome aberrations should be considered. We have confirmed a strong trend towards an association between the cosmic ray activity level and the incidence of DS.     

Formation of polar-body-like structures induced in polyspermic starfish oocytes that had been inseminated at the germinal vesicle stage

Immature starfish oocytes, which are arrested at the first meiotic prophase and contain a large nucleus called the germinal vesicle (GV), are known to accept multiple sperm on insemination. We found that if these polyspermic starfish oocytes are induced to mature, they often form small protrusion(s) adjacent to the first polar body emitted shortly earlier. We refer to these protrusion(s) as 'polar-body-like structures (PLS).' Fluorescent staining of PLS indicated that they were not merely cytoplasmic protrusions, but contained some chromatin. Maturing process of these polyspermic oocytes was examined by immnofluorescent staining, which showed that: (i) numerous sperm asters were observed after the onset of GV breakdown; (ii) before the first polar body (PB1) emission, a complex microtubular structure resembling a multipolar spindle was formed; and (iii) several isolated asters were observed after PB1 emission. These results indicate that PLS formation may be induced by interaction of meiosis-I spindle with paternal centrosomes incorporated at GV stage.     

基于Hartmann—Shack传感器的人眼波前像差重建技术

阐述了人眼波前像差的概念及其Zernike多项式表示方法,着重讨论了Hartmann—Shack传感器测量人眼像差的机理和人眼波前像差重建的方法,并对人眼波前像差重建系统进行了详细设计。该技术给人眼像差的校正以及角膜“个体化切削”的实现带来了新契机。     

Cancer progression by non-clonal chromosome aberrations

The establishment of the correct conceptual framework is vital to any scientific discipline including cancer research. Influenced by hematologic cancer studies, the current cancer concept focuses on the stepwise patterns of progression as defined by specific recurrent genetic aberrations. This concept has faced a tough challenge as the majority of cancer cases follow non-linear patterns and display stochastic progression. In light of the recent discovery that genomic instability is directly linked to stochastic non-clonal chromosome aberrations (NCCAs), and that cancer progression can be characterized as a dynamic relationship between NCCAs and recurrent clonal chromosome aberrations (CCAs), we propose that the dynamics of NCCAs is a key element for karyotypic evolution in solid tumors. To support this viewpoint, we briefly discuss various basic elements responsible for cancer initiation and progression within an evolutionary context. We argue that even though stochastic changes can be detected at various levels of genetic organization, such as at the gene level and epigenetic level, it is primarily detected at the chromosomal or genome level. Thus, NCCA-mediated genomic variation plays a dominant role in cancer progression. To further illustrate the involvement of NCCA/CCA cycles in the pattern of cancer evolution, four cancer evolutionary models have been proposed based on the comparative analysis of karyotype patterns of various types of cancer.     

Chlamydia trachomatis causes centrosomal defects resulting in chromosomal segregation abnormalities

Chlamydiae traffic along microtubules to the microtubule organizing center (MTOC) to establish an intracellular niche within the host cell. Trafficking to the MTOC is dynein dependent although the activating and cargo-linking function of the dynactin complex is supplanted by unknown chlamydial protein(s). We demonstrate that once localized to the MTOC, the chlamydial inclusion maintains a tight association with cellular centrosomes. This association is sustained through mitosis and leads to a significant increase in supernumerary centrosomes, abnormal spindle poles, and chromosomal segregation defects. Chlamydial infection thus can lead to chromosome instability in cells that recover from infection.     

Positioning centrosomes and spindle poles: looking at the periphery to find the centre

Centrosome positioning is tightly controlled throughout the cell cycle and probably shares common regulatory mechanisms with spindle-pole positioning. In this article, we detail the possible mechanisms controlling centrosome and spindle positioning in various organisms both in interphase and mitotic cells, and discuss recent findings showing how microtubule plus-end-associated proteins interact with the cell cortex. We suggest that microtubule plus-end complexes simultaneously regulate microtubule dynamics and microtubule anchoring at the cell periphery to allow proper centrosome and spindle-pole positioning.     

Anti-mitotic and anti-genotoxic effects of Plantago lanceolata aqueous extract on Allium cepa root tip meristem cells

Plantago is the most important genus of Plantaginaceae family and is used in traditional medicine around the world for different purposes. Plantago coronopus L., Plantago major L., Plantago media L. and Plantago lanceolata L. are most commonly used species of Plantago in traditional medicine in Turkey. The main goal of this study was to investigate the eventual anti-mitotic and anti-genotoxic effects of P. lanceolata L. leaf aqueous extracts (15 g/L and 30 g/L) on Allium cepa L. root tip meristem cells which were treated with 0.7% hydrogen peroxide. For this purpose, two different experiments were performed under the same conditions. In the first experiment, Allium cepa onion bulbs were treated with 0.7% H₂O₂ for 1 h. After the H₂O₂ treatment, the onion bulbs were treated with two different concentrations (15 g/L and 30 g/L) of P. lanceolata extracts for 24 h. In the second experiment, A. cepa onion bulbs were treated with two different extract concentrations (15 g/L and 30 g/L) for 24 h and then with 0.7% H₂O₂ for 1 h. The test concentrations were determined according to doses which are recommended in alternative medicinal usage by people. As positive and negative control 0.7% H₂O₂ and tap water was used, respectively. As a result, it was determined that aqueous extracts reduced mitotic index and chromosome aberrations in treatment groups in comparison with controls. These results showed that P. lanceolata aqueous extracts have anti-mitotic and anti-genotoxic effects.     

N-cadherin specifies first asymmetry in developing neurons

The precise polarization and orientation of developing neurons is essential for the correct wiring of the brain. In pyramidal excitatory neurons, polarization begins with the sprouting of opposite neurites, which later define directed migration and axo-dendritic domains. We here show that endogenous N-cadherin concentrates at one pole of the newborn neuron, from where the first neurite subsequently emerges. Ectopic N-cadherin is sufficient to favour the place of appearance of the first neurite. The Golgi and centrosome move towards this newly formed morphological pole in a second step, which is regulated by PI3K and the actin/microtubule cytoskeleton. Moreover, loss of function experiments in vivo showed that developing neurons with a non-functional N-cadherin misorient their cell axis. These results show that polarization of N-cadherin in the immediate post-mitotic stage is an early and crucial mechanism in neuronal polarity.     

Induction of robust de novo centrosome amplification, high-grade spindle multipolarity and metaphase catastrophe: a novel chemotherapeutic approach

Centrosome amplification (CA) and resultant chromosomal instability have long been associated with tumorigenesis. However, exacerbation of CA and relentless centrosome declustering engender robust spindle multipolarity (SM) during mitosis and may induce cell death. Recently, we demonstrated that a noscapinoid member, reduced bromonoscapine, (S)-3-(R)-9-bromo-5-(4,5-dimethoxy-1,3-dihydroisobenzofuran-1-yl)-4-methoxy-6-methyl-5,6,7,8-tetrahydro-[1,3]dioxolo-[4,5-g]isoquinoline (Red-Br-nos), induces reactive oxygen species (ROS)-mediated autophagy and caspase-independent death in prostate cancer PC-3 cells. Herein, we show that Red-Br-nos induces ROS-dependent DNA damage that resulted in high-grade CA and SM in PC-3 cells. Unlike doxorubicin, which causes double-stranded DNA breaks and chronic G2 arrest accompanied by ‘templated'' CA, Red-Br-nos-mediated DNA damage elicits de novo CA during a transient S/G2 stall, followed by checkpoint abrogation and mitotic entry to form aberrant mitotic figures with supernumerary spindle poles. Attenuation of multipolar phenotype in the presence of tiron, a ROS inhibitor, indicated that ROS-mediated DNA damage was partly responsible for driving CA and SM. Although a few cells (∼5%) yielded to aberrant cytokinesis following an ‘anaphase catastrophe'', most mitotically arrested cells (∼70%) succumbed to ‘metaphase catastrophe,'' which was caspase-independent. This report is the first documentation of rapid de novo centrosome formation in the presence of parent centrosome by a noscapinoid family member, which triggers death-inducing SM via a unique mechanism that distinguishes it from other ROS-inducers, conventional DNA-damaging agents, as well as other microtubule-binding drugs.