| 1. |
- Bastian, N., et al.
(författare)
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Evidence for environmentally dependent cluster disruption in M83
- 2011
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925. ; 417:1, s. l6-L10
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Tidskriftsartikel (refereegranskat)abstract
- Using multiwavelength imaging from the Wide Field Camera 3 on the Hubble Space Telescope we study the stellar cluster populations of two adjacent fields in the nearby face-on spiral galaxy, M83. The observations cover the galactic centre and reach out to similar to 6 kpc, thereby spanning a large range of environmental conditions, ideal for testing empirical laws of cluster disruption. The clusters are selected by visual inspection to be centrally concentrated, symmetric and resolved on the images. We find that a large fraction of objects detected by automated algorithms (e. g. SEXTRACTOR or DAOFIND) are not clusters, but rather are associations. These are likely to disperse into the field on time-scales of tens of Myr due to their lower stellar densities and not due to gas expulsion (i.e. they were never gravitationally bound). We split the sample into two discrete fields (inner and outer regions of the galaxy) and search for evidence of environmentally dependent cluster disruption. Colour-colour diagrams of the clusters, when compared to simple stellar population models, already indicate that a much larger fraction of the clusters in the outer field are older by tens of Myr than in the inner field. This impression is quantified by estimating each cluster's properties (age, mass and extinction) and comparing the age/mass distributions between the two fields. Our results are inconsistent with 'universal' age and mass distributions of clusters, and instead show that the ambient environment strongly affects the observed populations.
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| 2. |
- Bastian, N., et al.
(författare)
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Stellar clusters in M83 : formation, evolution, disruption and the influence of the environment
- 2012
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 419:3, s. 2606-2622
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Tidskriftsartikel (refereegranskat)abstract
- We study the stellar cluster population in two adjacent fields in the nearby, face-on spiral galaxy M83 using multiwavelength Wide Field Camera 3/Hubble Space Telescope imaging. After automatic detection procedures, the clusters are selected through visual inspection to be centrally concentrated, symmetric, and resolved on the images, which allows us to differentiate between clusters and likely unbound associations. We compare our sample with previous studies and show that the differences between the catalogues are largely due to the inclusion of a large numbers of diffuse associations within previous catalogues as well as the inclusion of the central starburst region, where the completeness limit is significantly worse than in the surrounding regions. We derive the size distribution of the clusters, which is well described by a lognormal distribution with a peak at ˜2.5 pc, and find evidence for an expansion in the half-light radius of clusters with age. The luminosity function of the clusters is well approximated by a power law with an index of -2 over most of the observed range; however, a steepening is seen at MV=-9.3 and -8.8 in the inner and outer fields, respectively. Additionally, we show that the cluster population is inconsistent with a pure power-law mass distribution, but instead exhibits a truncation at the high-mass end. If described as a Schechter function, the characteristic mass is 1.6 × 105 and 0.5 × 105 M&sun; for the inner and outer fields, respectively, in agreement with previous estimates of other cluster populations in spiral galaxies. Comparing the predictions of the mass-independent disruption (MID) and mass-dependent disruption (MDD) scenarios with the observed distributions, we find that both models can accurately fit the data. However, for the MID case, the fraction of clusters destroyed (or mass lost) per decade in age is dependent on the environment; hence, the age and mass distributions of clusters are not universal. In the MDD case, the disruption time-scale scales with galactocentric distance (being longer in the outer regions of the galaxy) in agreement with analytic and numerical predictions. Finally, we discuss the implications of our results on other extragalactic surveys, focusing on the fraction of stars that form in clusters and the need (or lack thereof) for infant mortality.
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| 3. |
- Lamers, Fieke, et al.
(författare)
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Targeted BCL2 inhibition effectively inhibits neuroblastoma tumour growth
- 2012
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Ingår i: European Journal of Cancer. - : Elsevier BV. - 1879-0852 .- 0959-8049. ; 48:16, s. 3093-3103
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Tidskriftsartikel (refereegranskat)abstract
- Genomic aberrations of key regulators of the apoptotic pathway have hardly been identified in neuroblastoma. We detected high BCL2 mRNA and protein levels in the majority of neuroblastoma tumours by Affymetrix expression profiling and Tissue Micro Array analysis. This BCL2 mRNA expression is strongly elevated compared to normal tissues and other malignancies. Most neuroblastoma cell lines lack this high BCL2 expression. Only two neuroblastoma cell lines (KCNR and SJNB12) show BCL2 expression levels representative for neuroblastoma tumours. To validate BCL2 as a therapeutic target in neuroblastoma we employed lentivirally mediated shRNA. Silencing of BCL2 in KCNR and SJNB12 resulted in massive apoptosis, while cell lines with low BCL2 expression were insensitive. Identical results were obtained by treatment of the neuroblastoma cell lines with the small molecule BCL2 inhibitor ABT263, which is currently being clinically evaluated. Combination assays of ABT263 with most classical cytostatics showed strong synergistic responses. Subcutaneous xenografts of a neuroblastoma cell line with high BCL2 expression in NMRI nu/nu mice showed a strong response to ABT263. These findings establish BCL2 as a promising drug target in neuroblastoma and warrant further evaluation of ABT263 and other BCL2 inhibiting drugs. (C) 2012 Elsevier Ltd. All rights reserved.
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| 4. |
- Gelter, Hans, et al.
(författare)
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Antarctic tourist experience : a comparison of SOI students with cruse tourists
- 2010
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Ingår i: 2010 International Polar Year Oslo Science Conference, Oslo, 8-12 Jun 2010.
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Konferensbidrag (refereegranskat)abstract
- In Antarctica tourism has increased drastically over the last decades with the numbers of ship-borne tourists increased by 430% and land-based tourists by 757% in the last 10-15 years. This drastic increase and its future predicted increase has evoked concerns among stakeholders about negative environmental impacts by the tourism industry in these fragile environments. This development has called for long term tourism policies as well as a request for research in polar tourism to understand its nature and its management and regulation. Much effort in polar tourism research has been allocated to define polar tourism as a legitimate area of scholarly inquiry. Despite the emerging polar tourism research we still know very little about the phenomenon of polar tourism. Most of polar tourism research has focused on patterns of tourism, tourist demands and tourist behaviour such as number of tourists, motivation, demographics, their routs, destinations, activities, attitudes, knowledge, skills and compositions of the travel groups. Since the creation of the International Association of Antarctica Tour Operators (IAATO) in 1991 there has been a reliable recording of tourist data in Antarctica. However, little information is available on the nature and quality of polar tourist experiences, knowledge (pre- and post visit), on-site experience and the tourists personal experiences of their impact on the environment. Particularly interesting is the effect of polar travel on the tourists´ post visit ambassadorial activities and the costs and benefits to polar travel associated with changing global climate patterns
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| 5. |
- Kuijt, Suzanne J. H., et al.
(författare)
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Interaction between the GROWTH-REGULATING FACTOR and KNOTTED1-LIKE HOMEOBOX Families of Transcription Factors1[W]
- 2014
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 164:4, s. 1952-1966
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Tidskriftsartikel (refereegranskat)abstract
- KNOTTED1-LIKE HOMEOBOX (KNOX) genes are important regulators of meristem function, and a complex network of transcription factors ensures tight control of their expression. Here, we show that members of the GROWTH-REGULATING FACTOR (GRF) family act as players in this network. A yeast (Saccharomyces cerevisiae) one-hybrid screen with the upstream sequence of the KNOX gene Oskn2 from rice (Oryza sativa) resulted in isolation of OsGRF3 and OsGRF10. Specific binding to a region in the untranslated leader sequence of Oskn2 was confirmed by yeast and in vitro binding assays. ProOskn2: beta-glucuronidase reporter expression was down-regulated by OsGRF3 and OsGRF10 in vivo, suggesting that these proteins function as transcriptional repressors. Likewise, we found that the GRF protein BGRF1 from barley (Hordeum vulgare) could act as a repressor on an intron sequence in the KNOX gene Hooded/Barley Knotted3 (Bkn3) and that AtGRF4, AtGRF5, and AtGRF6 from Arabidopsis (Arabidopsis thaliana) could repress KNOTTED-LIKE FROM ARABIDOPSIS THALIANA2 (KNAT2) promoter activity. OsGRF overexpression phenotypes in rice were consistent with aberrant meristematic activity, showing reduced formation of tillers and internodes and extensive adventitious root/shoot formation on nodes. These effects were associated with down-regulation of endogenous Oskn2 expression by OsGRF3. Conversely, RNA interference silencing of OsGRF3, OsGRF4, and OsGRF5 resulted in dwarfism, delayed growth and inflorescence formation, and up-regulation of Oskn2. These data demonstrate conserved interactions between the GRF and KNOX families of transcription factors in both monocot and dicot plants.
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| 6. |
- Lamers, Fieke, et al.
(författare)
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Identification of BIRC6 as a novel intervention target for neuroblastoma therapy
- 2012
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Ingår i: BMC Cancer. - : Springer Science and Business Media LLC. - 1471-2407. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Background: Neuroblastoma are pediatric tumors of the sympathetic nervous system with a poor prognosis. Apoptosis is often deregulated in cancer cells, but only a few defects in apoptotic routes have been identified in neuroblastoma. Methods: Here we investigated genomic aberrations affecting genes of the intrinsic apoptotic pathway in neuroblastoma. We analyzed DNA profiling data (CGH and SNP arrays) and mRNA expression data of 31 genes of the intrinsic apoptotic pathway in a dataset of 88 neuroblastoma tumors using the R2 bioinformatic platform (http://r2.amc.nl). BIRC6 was selected for further analysis as a tumor driving gene. Knockdown experiments were performed using BIRC6 lentiviral shRNA and phenotype responses were analyzed by Western blot and MTT-assays. In addition, DIABLO levels and interactions were investigated with immunofluorescence and co-immunoprecipitation. Results: We observed frequent gain of the BIRC6 gene on chromosome 2, which resulted in increased mRNA expression. BIRC6 is an inhibitor of apoptosis protein (IAP), that can bind and degrade the cytoplasmic fraction of the pro-apoptotic protein DIABLO. DIABLO mRNA expression was exceptionally high in neuroblastoma but the protein was only detected in the mitochondria. Upon silencing of BIRC6 by shRNA, DIABLO protein levels increased and cells went into apoptosis. Co-immunoprecipitation confirmed direct interaction between DIABLO and BIRC6 in neuroblastoma cell lines. Conclusion: Our findings indicate that BIRC6 may have a potential oncogenic role in neuroblastoma by inactivating cytoplasmic DIABLO. BIRC6 inhibition may therefore provide a means for therapeutic intervention in neuroblastoma.
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