Exciton dynamics within the band-edge state manifold of CdSe/ZnS and CdSe/CdS quantum dots (QDs) have been investigated. Low-temperature time-resolved photoluminescence (PL) experiments demonstrate ...that exciton relaxation is mediated by LO phonons, whereas an acoustic phonon bottleneck is observed for splitting energies lower than the optical phonon energy. This has important implications since the main source affecting exciton dephasing is considered to be a spin-flip process. Our results concur with recent observations of long exciton dephasing times in CdSe/CdS QDs and show a way to engineer nanoparticles with enhanced coherence time, a prerequisite for their use in quantum optical applications.
Abstract Lymphatic filariasis and onchocerciasis are diseases of severe morbidity that affect the poorest of the poor in the world. The diseases are caused by filarial nematodes that are transmitted ...by mosquitoes or biting blackflies and are endemic to more than 80 countries worldwide, mainly in the tropics and sub-tropics. Current control programs aim to eliminate the diseases by distributing antifilarial drugs. However, the primary effect of the drugs is to kill the microfilariae in the blood or skin, thus preventing uptake by the obligate insect vector. Since the adult worms live 10 years or longer, drug distribution requires many years of treatment, which is a heavy burden on the burgeoning health care systems. Sub-optimal response, possible resistance and inadequate population coverage lessen the chances for successful elimination in all endemic areas. The search for new drugs that could enhance elimination by permanently sterilizing or killing adult worms has identified the Wolbachia intracellular bacteria of filarial nematodes as a target. Depleting the obligate endosymbionts from the worms with doxycycline or rifampicin causes a permanent block in oogenesis, embryogenesis and development, and in slow death of the adult worms. These two antibiotics are suitable for individual drug administration, but caveats exist for their inclusion in broader drug administration programs. Here we review Wolbachia as targets for antifilarial drug discovery and highlight the natural product corallopyronin A as an effective drug that is currently being developed specifically for use against filarial nematodes.
By careful engineering of the core and shell dimensions in CdSe/CdS colloidal hetero‐nanocrystals, amplified spontaneous emission can be triggered from either the core, shell, or both states ...simultaneously. The ASE threshold is almost constant over a temperature interval of 5–325 K. This feature is unique to quantum dots and highlights their potential as a gain material, suitable for lasing at elevated temperatures.
Glioblastoma multiforme (GBM) is an invariably fatal central nervous system tumor despite treatment with surgery, radiation, and chemotherapy. Further insights into the molecular and cellular ...mechanisms that drive GBM formation are required to improve patient outcome. MicroRNAs are emerging as important regulators of cellular differentiation and proliferation, and have been implicated in the etiology of a variety of cancers, yet the role of microRNAs in GBM remains poorly understood. In this study, we investigated the role of microRNAs in regulating the differentiation and proliferation of neural stem cells and glioblastoma-multiforme tumor cells.
We used quantitative RT-PCR to assess microRNA expression in high-grade astrocytomas and adult mouse neural stem cells. To assess the function of candidate microRNAs in high-grade astrocytomas, we transfected miR mimics to cultured-mouse neural stem cells, -mouse oligodendroglioma-derived stem cells, -human glioblastoma multiforme-derived stem cells and -glioblastoma multiforme cell lines. Cellular differentiation was assessed by immunostaining, and cellular proliferation was determined using fluorescence-activated cell sorting.
Our studies revealed that expression levels of microRNA-124 and microRNA-137 were significantly decreased in anaplastic astrocytomas (World Health Organization grade III) and glioblastoma multiforme (World Health Organization grade IV) relative to non-neoplastic brain tissue (P < 0.01), and were increased 8- to 20-fold during differentiation of cultured mouse neural stem cells following growth factor withdrawal. Expression of microRNA-137 was increased 3- to 12-fold in glioblastoma multiforme cell lines U87 and U251 following inhibition of DNA methylation with 5-aza-2'-deoxycytidine (5-aza-dC). Transfection of microRNA-124 or microRNA-137 induced morphological changes and marker expressions consistent with neuronal differentiation in mouse neural stem cells, mouse oligodendroglioma-derived stem cells derived from S100 beta-v-erbB tumors and cluster of differentiation 133+ human glioblastoma multiforme-derived stem cells (SF6969). Transfection of microRNA-124 or microRNA-137 also induced G1 cell cycle arrest in U251 and SF6969 glioblastoma multiforme cells, which was associated with decreased expression of cyclin-dependent kinase 6 and phosphorylated retinoblastoma (pSer 807/811) proteins.
microRNA-124 and microRNA-137 induce differentiation of adult mouse neural stem cells, mouse oligodendroglioma-derived stem cells and human glioblastoma multiforme-derived stem cells and induce glioblastoma multiforme cell cycle arrest. These results suggest that targeted delivery of microRNA-124 and/or microRNA-137 to glioblastoma multiforme tumor cells may be therapeutically efficacious for the treatment of this disease.
The spatial organization, correct expression, repair, and segregation of eukaryotic genomes depend on cohesin, ring‐shaped protein complexes that are thought to function by entrapping DNA. It has ...been proposed that cohesin is recruited to specific genomic locations from distal loading sites by an unknown mechanism, which depends on transcription, and it has been speculated that cohesin movements along DNA could create three‐dimensional genomic organization by loop extrusion. However, whether cohesin can translocate along DNA is unknown. Here, we used single‐molecule imaging to show that cohesin can diffuse rapidly on DNA in a manner consistent with topological entrapment and can pass over some DNA‐bound proteins and nucleosomes but is constrained in its movement by transcription and DNA‐bound CCCTC‐binding factor (CTCF). These results indicate that cohesin can be positioned in the genome by moving along DNA, that transcription can provide directionality to these movements, that CTCF functions as a boundary element for moving cohesin, and they are consistent with the hypothesis that cohesin spatially organizes the genome via loop extrusion.
Synopsis
Human cohesin rings entrap DNA and rapidly translocate along DNA by diffusion. Cohesin can pass over small DNA‐bound proteins but is constrained in its movement by transcription and DNA‐bound CCCTC‐binding factor (CTCF).
Single‐molecule imaging of cohesin bound to immobilized DNA reveals that cohesin binds to DNA in a salt‐resistant manner and translocates with a diffusion coefficient higher than many other DNA‐binding proteins (1.72 ± 0.1 µm2/s).
Cohesin is released from DNA following cleavage of DNA or the cohesin ring, consistent with topological entrapment.
Cohesin can diffuse past obstacles with a diameter < ˜11 nm, including nucleosomes, but not those with a diameter > ˜21 nm, such as QDots.
CTCF constrains the movement of cohesin.
Transcribing T7 RNA polymerase provides directionality to cohesin.
Human cohesin rings entrap DNA and rapidly translocate along DNA by diffusion. Cohesin can pass over small DNA‐bound proteins but is constrained in its movement by transcription and DNA‐bound CCCTC‐binding factor (CTCF).
Capturing and controlling plasmons at buried interfaces with nanometre and femtosecond resolution has yet to be achieved and is critical for next generation plasmonic devices. Here we use light to ...excite plasmonic interference patterns at a buried metal-dielectric interface in a nanostructured thin film. Plasmons are launched from a photoexcited array of nanocavities and their propagation is followed via photon-induced near-field electron microscopy (PINEM). The resulting movie directly captures the plasmon dynamics, allowing quantification of their group velocity at ∼0.3 times the speed of light, consistent with our theoretical predictions. Furthermore, we show that the light polarization and nanocavity design can be tailored to shape transient plasmonic gratings at the nanoscale. This work, demonstrating dynamical imaging with PINEM, paves the way for the femtosecond and nanometre visualization and control of plasmonic fields in advanced heterostructures based on novel two-dimensional materials such as graphene, MoS
, and ultrathin metal films.
Nudibranchia, marine soft-bodied organisms, developed, due to the absence of a protective shell, different strategies to protect themselves against putative predators and fouling organisms. One ...strategy is to use chemical weapons to distract predators, as well as pathogenic microorganisms. Hence, these gastropods take advantage of the incorporation of chemical molecules. Thereby the original source of these natural products varies; it might be the food source,
synthesis from the sea slug, or biosynthesis by associated bacteria. These bioactive molecules applied by the slugs can become important drug leads for future medicinal drugs. To test the potential of the associated bacteria, the latter were isolated from their hosts, brought into culture and extracts were prepared and tested for antimicrobial activities. From 49 isolated bacterial strains 35 showed antibiotic activity. The most promising extracts were chosen for further testing against relevant pathogens. In that way three strains showing activity against methicillin resistant
and one strain with activity against enterohemorrhagic
, respectively, were identified. The obtained results indicate that the sea slug associated microbiome is a promising source for bacterial strains, which hold the potential for the biotechnological production of antibiotics.
The sensitivity and response of northern hemisphere altitudinal and polar treelines to environmental change are increasingly discussed in terms of climate change, often forgetting that climate is ...only one aspect of environmental variation. As treeline heterogeneity increases from global to regional and smaller scales, assessment of treeline sensitivity at the landscape and local scales requires a more complex approach than at the global scale. The time scale (short-, medium-, long-term) also plays an important role when considering treeline sensitivity. The sensitivity of the treeline to a changing environment varies among different types of treeline. Treelines controlled mainly by orographic influences are not very susceptible to the effects of warming climates. Greatest sensitivity can be expected in anthropogenic treelines after the cessation of human activity. However, tree invasion into former forested areas above the anthropogenic forest limit is controlled by site conditions, and in particular, by microclimates and soils. Apart from changes in tree physiognomy, the spontaneous advance of young growth of forest-forming tree species into present treeless areas within the treeline ecotone and beyond the tree limit is considered to be the best indicator of treeline sensitivity to environmental change. The sensitivity of climatic treelines to climate warming varies both in the local and regional topographical conditions. Furthermore, treeline history and its after-effects also play an important role. The sensitivity of treelines to changes in given factors (e.g. winter snow pack, soil moisture, temperature, evaporation, etc.) may vary among areas with differing climatic characteristics. In general, forest will not advance in a closed front but will follow sites that became more favourable to tree establishment under the changed climatic conditions.
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