Independent, Rapid and Targeted Loss of Highly Repetitive DNA in Natural and Synthetic Allopolyploids of Nicotiana tabacum

Allopolyploidy (interspecific hybridisation and polyploidy) has played a significant role in the evolutionary history of angiosperms and can result in genomic, epigenetic and transcriptomic perturbations. We examine the immediate effects of allopolyploidy on repetitive DNA by comparing the genomes of synthetic and natural Nicotiana tabacum with diploid progenitors N. tomentosiformis (paternal progenitor) and N. sylvestris (maternal progenitor). Using next generation sequencing, a recently developed graph-based repeat identification pipeline, Southern blot and fluorescence in situ hybridisation (FISH) we characterise two highly repetitive DNA sequences (NicCL3 and NicCL7/30). Analysis of two independent high-throughput DNA sequencing datasets indicates NicCL3 forms 1.6–1.9% of the genome in N. tomentosiformis, sequences that occur in multiple, discontinuous tandem arrays scattered over several chromosomes. Abundance estimates, based on sequencing depth, indicate NicCL3 is almost absent in N. sylvestris and has been dramatically reduced in copy number in the allopolyploid N. tabacum. Surprisingly elimination of NicCL3 is repeated in some synthetic lines of N. tabacum in their forth generation. The retroelement NicCL7/30, which occurs interspersed with NicCL3, is also under-represented but to a much lesser degree, revealing targeted elimination of the latter. Analysis of paired-end sequencing data indicates the tandem component of NicCL3 has been preferentially removed in natural N. tabacum, increasing the proportion of the dispersed component. This occurs across multiple blocks of discontinuous repeats and based on the distribution of nucleotide similarity among NicCL3 units, was concurrent with rounds of sequence homogenisation

The Winchcombe meteorite, a unique and pristine witness from the outer solar system.

Direct links between carbonaceous chondrites and their parent bodies in the solar system are rare. The Winchcombe meteorite is the most accurately recorded carbonaceous chondrite fall. Its pre-atmospheric orbit and cosmic-ray exposure age confirm that it arrived on Earth shortly after ejection from a primitive asteroid. Recovered only hours after falling, the composition of the Winchcombe meteorite is largely unmodified by the terrestrial environment. It contains abundant hydrated silicates formed during fluid-rock reactions, and carbon- and nitrogen-bearing organic matter including soluble protein amino acids. The near-pristine hydrogen isotopic composition of the Winchcombe meteorite is comparable to the terrestrial hydrosphere, providing further evidence that volatile-rich carbonaceous asteroids played an important role in the origin of Earth's water

Review of the projected impacts of climate change on coastal fishes in southern Africa

The coastal zone represents one of the most economically and ecologically important ecosystems on the planet, none more so than in southern Africa. This manuscript examines the potential impacts of climate change on the coastal fishes in southern Africa and provides some of the first information for the Southern Hemisphere, outside of Australasia. It begins by describing the coastal zone in terms of its physical characteristics, climate, fish biodiversity and fisheries. The region is divided into seven biogeographical zones based on previous descriptions and interpretations by the authors. A global review of the impacts of climate change on coastal zones is then applied to make qualitative predictions on the likely impacts of climate change on migratory, resident, estuarine-dependent and catadromous fishes in each of these biogeographical zones. In many respects the southern African region represents a microcosm of climate change variability and of coastal habitats. Based on the broad range of climate change impacts and life history styles of coastal fishes, the predicted impacts on fishes will be diverse. If anything, this review reveals our lack of fundamental knowledge in this field, in particular in southern Africa. Several research priorities, including the need for process-based fundamental research programs are highlighted

Search for large missing transverse momentum in association with one top-quark in proton-proton collisions at s√=13 TeV with the ATLAS detector

This paper describes a search for events with one top-quark and large missing transverse momentum in the final state. Data collected during 2015 and 2016 by the ATLAS experiment from 13 TeV proton–proton collisions at the LHC corresponding to an integrated luminosity of 36.1 fb−1 are used. Two channels are considered, depending on the leptonic or the hadronic decays of the W boson from the top quark. The obtained results are interpreted in the context of simplified models for dark-matter production and for the single production of a vector-like T quark. In the absence of significant deviations from the Standard Model background expectation, 95% confidence-level upper limits on the corresponding production cross-sections are obtained and these limits are translated into constraints on the parameter space of the models considered

Type 1 astrocytes inhibit myelination by adult rat oligodendrocytes in vitro

We have determined the effect of Type 1 astrocytes on the myelination of dorsal root ganglion cell axons by oligodendrocytes obtained from adult animals. Experiments were initiated by the addition of oligodendrocytes [purified either by density gradient centrifugation and treatment in culture with 5-fluorodeoxyuridine (FdU) or by fluorescence-activated cell sorting after immunostaining with antigalactocerebroside antibody] to cultures of purified neurons. In control conditions, the added oligodendrocytes proliferate and, after 4 weeks, accomplish substantial myelination of the sensory axons. Type 1 astrocytes (purified from cultures of dissociated newborn rat cerebral cortex by vigorous shaking to remove less adherent cells) or fibroblasts (purified from cultures of cranial periosteum by serial replating) were added to some of these cultures after the oligodendrocytes had attached and started to proliferate. We observed that the added Type 1 astrocytes, but not the added fibroblasts, strongly inhibited myelination and caused decreased oligodendrocyte proliferation or survival. These effects of added Type 1 astrocytes were reproduced with Type 1 astrocyte-conditioned medium. We conclude that Type 1 astrocytes can release soluble factors that inhibit oligodendrocyte myelination