297 research outputs found
Water induced sediment levitation enhances downslope transport on Mars
On Mars, locally warm surface temperatures (~293 K) occur, leading to the possibility of (transient) liquid water on the surface. However, water exposed to the martian atmosphere will boil, and the sediment transport capacity of such unstable water is not well understood. Here, we present laboratory studies of a newly recognized transport mechanism: “levitation” of saturated sediment bodies on a cushion of vapor released by boiling. Sediment transport where this mechanism is active is about nine times greater than without this effect, reducing the amount of water required to transport comparable sediment volumes by nearly an order of magnitude. Our calculations show that the effect of levitation could persist up to ~48 times longer under reduced martian gravity. Sediment levitation must therefore be considered when evaluating the formation of recent and present-day martian mass wasting features, as much less water may be required to form such features than previously thought
Brain architecture in the terrestrial hermit crab Coenobita clypeatus (Anomura, Coenobitidae), a crustacean with a good aerial sense of smell
<p>Abstract</p> <p>Background</p> <p>During the evolutionary radiation of Crustacea, several lineages in this taxon convergently succeeded in meeting the physiological challenges connected to establishing a fully terrestrial life style. These physiological adaptations include the need for sensory organs of terrestrial species to function in air rather than in water. Previous behavioral and neuroethological studies have provided solid evidence that the land hermit crabs (Coenobitidae, Anomura) are a group of crustaceans that have evolved a good sense of aerial olfaction during the conquest of land. We wanted to study the central olfactory processing areas in the brains of these organisms and to that end analyzed the brain of <it>Coenobita clypeatus </it>(Herbst, 1791; Anomura, Coenobitidae), a fully terrestrial tropical hermit crab, by immunohistochemistry against synaptic proteins, serotonin, FMRFamide-related peptides, and glutamine synthetase.</p> <p>Results</p> <p>The primary olfactory centers in this species dominate the brain and are composed of many elongate olfactory glomeruli. The secondary olfactory centers that receive an input from olfactory projection neurons are almost equally large as the olfactory lobes and are organized into parallel neuropil lamellae. The architecture of the optic neuropils and those areas associated with antenna two suggest that <it>C. clypeatus </it>has visual and mechanosensory skills that are comparable to those of marine Crustacea.</p> <p>Conclusion</p> <p>In parallel to previous behavioral findings of a good sense of aerial olfaction in C. clypeatus, our results indicate that in fact their central olfactory pathway is most prominent, indicating that olfaction is a major sensory modality that these brains process. Interestingly, the secondary olfactory neuropils of insects, the mushroom bodies, also display a layered structure (vertical and medial lobes), superficially similar to the lamellae in the secondary olfactory centers of <it>C. clypeatus</it>. More detailed analyses with additional markers will be necessary to explore the question if these similarities have evolved convergently with the establishment of superb aerial olfactory abilities or if this design goes back to a shared principle in the common ancestor of Crustacea and Hexapoda.</p
Magnetic Flux Transport by turbulent reconnection in astrophysical flows
The role of MHD turbulence in astrophysical environments is still highly
debated. An important question that permeates this debate is the transport of
magnetic flux. This is particularly important, for instance, in the context of
star formation. When clouds collapse gravitationally to form stars, there must
be some magnetic flux transport. otherwise the new born stars would have
magnetic fields several orders of magnitude larger than the observed ones.
Also, the magnetic flux that is dragged in the late stages of the formation of
a star can remove all the rotational support from the accretion disk that grows
around the protostar. The efficiency of the mechanism which is often invoked to
allow the transport of magnetic fields in the different stages of star
formation, namely, the ambipolar diffusion, has been lately put in check. We
here discuss an alternative mechanism for magnetic flux transport which is
based on turbulent fast magnetic reconnection. We review recent results
obtained from 3D MHD numerical simulations that indicate that this mechanism is
very efficient for decoupling and transport magnetic flux from the inner denser
regions to the outskirts of collapsing clouds in the different stages of star
formation. We also discuss this mechanism in the context of dynamo processes
and speculate that it can play a role both in the solar dynamo and in accretion
disk dynamo processes.Comment: 10 pages, 2 figures, review submitted to Physica Script
Contributions of Histone H3 Nucleosome Core Surface Mutations to Chromatin Structures, Silencing and DNA Repair
Histone H3 mutations in residues that cluster in a discrete region on the nucleosome surface around lysine 79 of H3 affect H3-K79 methylation, impair transcriptional silencing in subtelomeric chromatin, and reveal distinct contributions of histone H3 to various DNA-damage response and repair pathways. These residues might act by recruitment of silencing and DNA-damage response factors. Alternatively, their location on the nucleosome surface suggests a possible involvement in nucleosome positioning, stability and nucleosome interactions. Here, we show that the yeast H3 mutants hht2-T80A, hht2-K79E, hht2-L70S, and hht2-E73D show normal nucleosome positioning and stability in minichromosomes. However, loss of silencing in a subtelomeric URA3 gene correlates with a shift of the promoter nucleosome, while nucleosome positions and stability in the coding region are maintained. Moreover, the H3 mutants show normal repair of UV lesions by photolyase and nucleotide excision repair in minichromosomes and slightly enhanced repair in the subtelomeric region. Thus, these results support a role of those residues in the recruitment of silencing proteins and argue against a general role in nucleosome organization
Gefitinib (‘Iressa’, ZD1839) inhibits the growth response of bladder tumour cell lines to epidermal growth factor and induces TIMP2
The 3′ processing factor CstF functions in the DNA repair response
Following DNA damage, mRNA levels decrease, reflecting a coordinated interaction of the DNA repair, transcription and RNA processing machineries. In this study, we provide evidence that transcription and polyadenylation of mRNA precursors are both affected in vivo by UV treatment. We next show that the polyadenylation factor CstF, plays a direct role in the DNA damage response. Cells with reduced levels of CstF display decreased viability following UV treatment, reduced ability to ubiquitinate RNA polymerase II (RNAP II), and defects in repair of DNA damage. Furthermore, we show that CstF, RNAP II and BARD1 are all found at sites of repaired DNA. Our results indicate that CstF plays an active role in the response to DNA damage, providing a link between transcription-coupled RNA processing and DNA repair
The great melting pot. Common sole population connectivity assessed by otolith and water fingerprints
Quantifying the scale and importance of individual dispersion between populations and life stages is a key challenge in marine ecology. The common sole (Solea solea), an important commercial flatfish in the North Sea, Atlantic Ocean and the Mediterranean Sea, has a marine pelagic larval stage, a benthic juvenile stage in coastal nurseries (lagoons, estuaries or shallow marine areas) and a benthic adult stage in deeper marine waters on the continental shelf. To date, the ecological connectivity among these life stages has been little assessed in the Mediterranean. Here, such an assessment is provided for the first time for the Gulf of Lions, NW Mediterranean, based on a dataset on otolith microchemistry and stable isotopic composition as indicators of the water masses inhabited by individual fish. Specifically, otolith Ba/Ca and Sr/Ca profiles, and delta C-13 and delta O-18 values of adults collected in four areas of the Gulf of Lions were compared with those of young-of-the-year collected in different coastal nurseries. Results showed that a high proportion of adults (>46%) were influenced by river inputs during their larval stage. Furthermore Sr/Ca ratios and the otolith length at one year of age revealed that most adults (similar to 70%) spent their juvenile stage in nurseries with high salinity, whereas the remainder used brackish environments. In total, data were consistent with the use of six nursery types, three with high salinity (marine areas and two types of highly saline lagoons) and three brackish (coastal areas near river mouths, and two types of brackish environments), all of which contributed to the replenishment of adult populations. These finding implicated panmixia in sole population in the Gulf of Lions and claimed for a habitat integrated management of fisherie
Decreased transcription-coupled nucleotide excision repair capacity is associated with increased p53- and MLH1-independent apoptosis in response to cisplatin
Abstract
Background
One of the most commonly used classes of anti-cancer drugs presently in clinical practice is the platinum-based drugs, including cisplatin. The efficacy of cisplatin therapy is often limited by the emergence of resistant tumours following treatment. Cisplatin resistance is multi-factorial but can be associated with increased DNA repair capacity, mutations in p53 or loss of DNA mismatch repair capacity.
Methods
RNA interference (RNAi) was used to reduce the transcription-coupled nucleotide excision repair (TC-NER) capacity of several prostate and colorectal carcinoma cell lines with specific defects in p53 and/or DNA mismatch repair. The effect of small inhibitory RNAs designed to target the CSB (Cockayne syndrome group B) transcript on TC-NER and the sensitivity of cells to cisplatin-induced apoptosis was determined.
Results
These prostate and colon cancer cell lines were initially TC-NER proficient and RNAi against CSB significantly reduced their DNA repair capacity. Decreased TC-NER capacity was associated with an increase in the sensitivity of tumour cells to cisplatin-induced apoptosis, even in p53 null and DNA mismatch repair-deficient cell lines.
Conclusion
The present work indicates that CSB and TC-NER play a prominent role in determining the sensitivity of tumour cells to cisplatin even in the absence of p53 and DNA mismatch repair. These results further suggest that CSB represents a potential target for cancer therapy that may be important to overcome resistance to cisplatin in the clinic
The phosphatase and tensin homologue deleted on chromosome 10 mediates radiosensitivity in head and neck cancer
BACKGROUND: For locally advanced squamous cell carcinoma of the head and neck (HNSCC), the recurrence rate after surgery and postoperative radiotherapy is between 20 and 40%, and the 5- year overall survival rate is similar to 50%. Presently, no markers exist to accurately predict treatment outcome. Expression of proteins in the human epidermal growth factor receptor (EGFR) pathway has been reported as a prognostic marker in several types of cancer. METHODS: The aim of this study was to investigate the prognostic value of proteins in the EGFR pathway in HNSCC. For this purpose, we collected surgically resected tissue of 140 locally advanced head and neck cancer patients, all treated with surgery and postoperative radiotherapy. RESULTS: In a multivariate analysis, expression of the phosphatase and tensin homologue deleted on chromosome 10 (PTEN) was significantly related to worse locoregional control (LRC; HR: 2.2, 95% CI: 1.1-4.6; P = 0.03), independent of lymph node metastases (HR: 5.6, 95% CI: 1.2-27.4; P = 0.03) and extranodal spread (HR: 2.7; 95% CI: 1.2- 6.5; P = 0.02). In vitro clonogenic radiosensitivity assays confirmed that overexpression of PTEN resulted in increased radioresistance. CONCLUSION: Our study is the first report showing that expression of PTEN mediates radiosensitivity in vitro and that increased expression in advanced HNSCC predicts worse LRC. British Journal of Cancer (2010) 102, 1778-1785. doi: 10.1038/sj.bjc.6605707 www.bjcancer.com Published online 25 May 2010 (C) 2010 Cancer Research U
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