Crossovers (COs) between homologous chromosomes ensure their faithful segregation during meiosis. We identify C. elegans COSA-1, a cyclin-related protein conserved in metazoa, as a key component ...required to convert meiotic double-strand breaks (DSBs) into COs. During late meiotic prophase, COSA-1 localizes to foci that correspond to the single CO site on each homolog pair and indicate sites of eventual concentration of other conserved CO proteins. Chromosomes gain and lose competence to load CO proteins during meiotic progression, with competence to load COSA-1 requiring prior licensing. Our data further suggest a self-reinforcing mechanism maintaining CO designation. Modeling of a nonlinear dose-response relationship between IR-induced DSBs and COSA-1 foci reveals efficient conversion of DSBs into COs when DSBs are limiting and a robust capacity to limit cytologically differentiated CO sites when DSBs are in excess. COSA-1 foci serve as a unique live cell readout for investigating CO formation and CO interference.
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► C. elegans COSA-1 promotes meiotic crossovers (COs) and concentrates at CO sites ► Competence to install COSA-1 at designated CO sites requires a prior licensing event ► Robust homeostasis and interference yield one marked CO site per chromosome pair ► COSA-1 foci act as a DSB dosimeter and a live cell reporter of CO interference
The identification of C. elegans COSA-1, a cyclin-related protein conserved in metazoan, as a marker of nascent CO sites provides unprecedented opportunities for investigating the mechanisms that promote CO formation and that restrict the accumulation of CO activity to bona fide CO sites.
For most organisms, chromosome segregation during meiosis relies on deliberate induction of DNA double-strand breaks (DSBs) and repair of a subset of these DSBs as inter-homolog crossovers (COs). ...However, timing and levels of DSB formation must be tightly controlled to avoid jeopardizing genome integrity. Here we identify the DSB-2 protein, which is required for efficient DSB formation during C. elegans meiosis but is dispensable for later steps of meiotic recombination. DSB-2 localizes to chromatin during the time of DSB formation, and its disappearance coincides with a decline in RAD-51 foci marking early recombination intermediates and precedes appearance of COSA-1 foci marking CO-designated sites. These and other data suggest that DSB-2 and its paralog DSB-1 promote competence for DSB formation. Further, immunofluorescence analyses of wild-type gonads and various meiotic mutants reveal that association of DSB-2 with chromatin is coordinated with multiple distinct aspects of the meiotic program, including the phosphorylation state of nuclear envelope protein SUN-1 and dependence on RAD-50 to load the RAD-51 recombinase at DSB sites. Moreover, association of DSB-2 with chromatin is prolonged in mutants impaired for either DSB formation or formation of downstream CO intermediates. These and other data suggest that association of DSB-2 with chromatin is an indicator of competence for DSB formation, and that cells respond to a deficit of CO-competent recombination intermediates by prolonging the DSB-competent state. In the context of this model, we propose that formation of sufficient CO-competent intermediates engages a negative feedback response that leads to cessation of DSB formation as part of a major coordinated transition in meiotic prophase progression. The proposed negative feedback regulation of DSB formation simultaneously (1) ensures that sufficient DSBs are made to guarantee CO formation and (2) prevents excessive DSB levels that could have deleterious effects.
Mining causes extensive damage to aquatic ecosystems via acidification, heavy metal pollution, sediment loading, and Ca decline. Yet little is known about the effects of mining on freshwater systems ...in the Southern Hemisphere. A case in point is the region of western Tasmania, Australia, an area extensively mined in the 19th century, resulting in severe environmental contamination. In order to assess the impacts of mining on aquatic ecosystems in this region, we present a multiproxy investigation of the lacustrine sediments from Owen Tarn, Tasmania. This study includes a combination of radiometric dating (14C and 210Pb), sediment geochemistry (XRF and ICP-MS), pollen, charcoal and diatoms. Generalised additive mixed models were used to test if changes in the aquatic ecosystem can be explained by other covariates. Results from this record found four key impact phases: (1) Pre-mining, (2) Early mining, (3) Intense mining, and (4) Post-mining. Before mining, low heavy metal concentrations, slow sedimentation, low fire activity, and high biomass indicate pre-impact conditions. The aquatic environment at this time was oligotrophic and dystrophic with sufficient light availability, typical of western Tasmanian lakes during the Holocene. Prosperous mining resulted in increased burning, a decrease in landscape biomass and an increase in sedimentation resulting in decreased light availability of the aquatic environment. Extensive mining at Mount Lyell in the 1930s resulted in peak heavy metal pollutants (Pb, Cu and Co) and a further increase in inorganic inputs resulted in a disturbed low light lake environment (dominated by Hantzschia amphioxys and Pinnularia divergentissima). Following the closure of the Mount Lyell Co. in 1994 CE, Ca declined to below pre-mining levels resulting in a new diatom assemblage and deformed diatom valves. Therefore, the Owen Tarn record demonstrates severe sediment pollution and continued impacts of mining long after mining has stopped at Mt. Lyell Mining Co.
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•Mining has caused extensive environmental degradation in Tasmania.•A palaeoenvironmental study investigated the impacts of mining on an aquatic ecosystem.•The Owen Tarn record revealed four key impact phases.•Pre-mining, Early mining, Intense mining, and Post mining impacts.•Owen Tarn is impacted by severe sediment pollution and Ca decline from mining.
The Owen Tarn record revealed four impact phases: Pre-mining, Early mining, Intense mining, and Post mining. Mining caused severe sediment pollution and Ca decline in the aquatic environment.
Nickel catalysts were prepared on single-oxide supports of Al2O3, CeO2, MgO and ZrO2 by impregnation of the oxide with a solution of Ni(NO3)2 in methanol. The catalysts were characterized by N2 ...physisorption (BET method), TPR, XRD, SEM and Raman spectroscopy and tested in dry reforming of ethanol (DRE). It was observed that the interaction with the support and Ni reducibility depended on the support used. According to TPR results, NiO species supported on CeO2 and Al2O3 were the easiest to reduce. Possibly, this behavior combined to redox properties of CeO2 inhibited side undesirable reactions and contributed to the higher selectivity for H2 on the NiCe catalyst. The catalytic test at 750°C on NiCe showed better H2 selectivity than the test at 700°C, suggesting that the higher temperature enhanced CO2 conversion and hindered carbon deposition in dry reforming of ethanol reactions.
•Ni catalysts were prepared by impregnation using methanol as solvent.•The interaction with the support and Ni reducibility depended on the support used.•NiO species supported on CeO2 were the easiest to reduce.•The NiCe catalyst showed the highest selectivity for hydrogen production.•Filamentous carbon species were observed in Raman spectra and SEM image of NiCe.
In the paper, the analytical forms of fractional order derivatives of sinusoidal function according to definitions of Riemann - Liouville and Caputo are presented. To determine the analytical form of ...the integrals appearing in definitions of derivatives of fractional order the Lommel functions from hypergeometrical functions family were applied. With the use of properties of the derivatives of fractional order - differential-integral there were presented the conception of generalized element of a single equation, which depending on the value of the derivative order, can be inductor, resistor, capacitor, or a hypothetical element of a fractional order differential equation.
Context
Transdisciplinary research is important where information from multiple fields is required to develop ecologically and culturally appropriate environmental planning that protects local ...conservation and socio-cultural values.
Objectives
Here, we describe research to inform ecosystem restoration and conservation of Chumbrumba Swamp within the Wet Tropics World Heritage Area, Australia. Many such open wetlands in the region have been degraded through agriculture and pastoral production, but there has been little research into their status, history and conservation needs.
Methods
The recent to pre-European settlement history of the site was explored, along with spatial variation of vegetation communities at the site, and these data integrated with historical and ethnographical information on the site and its cultural values.
Results
The botanical and palaeoecological analyses showed that Chumbrumba Swamp comprises a unique and highly sensitive ecosystem mosaic with high biodiversity. An endangered ecosystem complex, 82 vascular plant species, several disjunct or endemic taxa, and species at new northern range limits were recorded within its 20 ha area. The site comprises a stable swamp site with fringing woodland and rainforest that has persisted for around 5000 years. European settlement overlaid changes in the vegetation from disturbance (e.g. fire, clearing, grazing). However, fire also affected the swamp site during pre-European times.
Conclusions
Historical and ethnographic information contextualised the biophysical data and confirmed the cultural importance of the site and the dynamic interactions between ‘people and nature’. These results have been used to inform environmental restoration and validate the importance of a transdisciplinary and precautionary approach to planning wetland restoration and conservation.
Addition of β-acids extracted from hop at different levels (0, 30mgkg−1, 60mgkg−1, 240mgkg−1) to the diet of broiler chickens demonstrated significant effects on the average concentration of polar ...metabolites and fatty acids of relevance for meat quality. The largest metabolic differences between control group and chicken fed different levels of β-acids were achieved using 30mgkg−1 of supplement. As determined by EPR spin-trapping, increased redox stability was also obtained for meat from chicken fed 30mgkg−1 of β-acids which also had highest level of endogenous antioxidants, especially anserine, carnosine, NADH and PUFAs. Diet and storage period were found to affect protein oxidation and myosin and actin were recognized as the main targets of protein oxidation. Myofibrillar proteins from chicken fed hop β-acids showed to be less susceptible to oxidation. A moderated level of hop β-acids as dietary supplement accordingly improve the overall redox stability, protecting myofibrillar proteins and fatty acids against oxidation and improve the nutritional properties of meat from broiler chickens.
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•Hop β-acids added to chickens diet affects polar metabolites and fatty acids profile.•Meat from chicken fed 30mgkg−1feed of β-acids shows lower tendency to radical formation.•Myofibrillar proteins in meat from chicken supplemented with β-acids are protected against oxidation.
Most promoters in yeast contain a nucleosome-depleted region (NDR), but the mechanisms by which NDRs are established and maintained in vivo are currently unclear. We have examined how genome-wide ...nucleosome placement is altered in the absence of two distinct types of nucleosome remodeling activity. In mutants of both SNF2, which encodes the ATPase component of the Swi/Snf remodeling complex, and ASF1, which encodes a histone chaperone, distinct sets of gene promoters carry excess nucleosomes in their NDRs relative to wild-type. In snf2 mutants, excess promoter nucleosomes correlate with reduced gene expression. In both mutants, the excess nucleosomes occupy DNA sequences that are energetically less favorable for nucleosome formation, indicating that intrinsic histone-DNA interactions are not sufficient for nucleosome positioning in vivo, and that Snf2 and Asf1 promote thermodynamic equilibration of nucleosomal arrays. Cells lacking SNF2 or ASF1 still accomplish the changes in promoter nucleosome structure associated with large-scale transcriptional reprogramming. However, chromatin reorganization in the mutants is reduced in extent compared to wild-type cells, even though transcriptional changes proceed normally. In summary, active remodeling is required for distributing nucleosomes to energetically favorable positions in vivo and for reorganizing chromatin in response to changes in transcriptional activity.
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