We report detailed high precision combined single grain U-Pb and Lu-Hf studies of early zircons to obtain more reliable indications of the extent of mantle depletion and crustal recycling in the ...Archean. Despite the possibility that MC-ICPMS affords for precise Hf isotopic measurement of single zircons, the complexity of grain populations adds uncertainty to initial isotopic ratios. Multiple episodes of zircon growth and ancient Pb loss, common in early Archaean rocks, result in
207Pb/
206Pb ages, and in some cases
176Hf/
176Hf ratios, that are variable between and within zircon grains. In order to evaluate the role of heterogeneity of zircon populations and to obtain the most reliable ε
Hf(T), we have analysed several abraded zircon grains (from two to eleven) from each of several samples for both Lu-Hf and U-Pb. Hf isotopic analyses with precision better than 1 to 1.5 ε-units (2σ) were obtained from grains weighing between 3 and 10 micrograms. The observed internal variations in age, U-Pb discordance, and Hf isotopic composition have been tested against models of disturbance of isotopic systems in zircon. Application of the U-Pb and Lu-Hf methods to the same zircon grains and analysis of single grains appears to be crucial for finding closed geochemical systems and thereby obtaining reliable Hf isotope data from early Archaean rocks. The precision and accuracy of Hf isotopic data obtained with the approach presented here are limited mainly by the sensitivity of Hf isotopic analyses, and may be greatly improved with the progress of analytical techniques.
Following our earlier study of the Jack Hill’s metaconglomerate in which we found no significant trace of depleted mantle-like Hf in >3.8 Ga zircons we have studied zircons from 15 rocks from four early-middle Archaean areas. Four ca. 3.6 Ga gneisses from the Acasta Gneiss Complex of Northwest Canada contain zircons with ε
Hf(T) between +0.7 and −4.1, as well as xenocrystic zircon grains with unradiogenic Hf. Some older grains have reset U-Pb systems, but preserve their Hf isotopic composition. The 3.62 to 3.73 Ga Amı̂tsoq gneisses, West Greenland, have ε
Hf(T) between +1.4 and +2.6, while 3.52 to 3.32 Ga gneisses and felsic metavolcanics from Barberton and Pilbara yielded ε
Hf(T) between +1.9 and +4.2. These early-middle Archaean complexes were formed from crust derived from previously depleted mantle. These complexes grew over the first 100 to 200 m.y. of their evolution mainly by addition of juvenile crust, while reworking of older crust was less significant. The higher ε
Hf(T) values in the Barberton and Pilbara rocks compared to the Amı̂tsoq gneisses are consistent with uniform or increasing mantle depletion during the early Archaean. The Acasta Gneiss Complex was probably formed from very old crust (3.8 to 4.0 Ga) that was extensively reworked during the Archaean. Both U-Pb and Hf isotopic data suggest the similarities between the evolution of the Acasta Gneiss Complex and the source of 4.2 to 3.4 Ga Jack Hills detrital zircons.
For nearly half a century, Professor M. A. K. Halliday has been
enriching the discipline of linguistics with his keen insights into the social
semiotic phenomenon we call language. This ten-volume ...series presents the seminal
works of Professor Halliday. This third volume includes papers that explore
different aspects of language from a systemic functional perspective. The papers are
organized into three sections: the place of linguistics as a discipline; linguistics
and language; and language as social semiotic. In addition, there is a new work from
Professor Halliday, entitled ‘On the “architecture” of human
language', in which he focuses on the assumptions or working hypotheses that
enabled him to explore important questions about this massive semiotic power called
’language'.
High levels of hydrological connectivity during seasonal flooding provide significant opportunities for movements of fish between rivers and their floodplains, estuaries and the sea, possibly ...mediating food web subsidies among habitats. To determine the degree of utilisation of food sources from different habitats in a tropical river with a short floodplain inundation duration (~ 2 months), stable isotope ratios in fishes and their available food were measured from three habitats (inundated floodplain, dry season freshwater, coastal marine) in the lower reaches of the Mitchell River, Queensland (Australia). Floodplain food sources constituted the majority of the diet of largebodied fishes (barramundi Lates calcarifer, catfish Neoarius graeffei) captured on the floodplain in the wet season and for gonadal tissues of a common herbivorous fish (gizzard shad Nematalosa come), the latter suggesting that critical reproductive phases are fuelled by floodplain production. Floodplain food sources also subsidised barramundi from the recreational fishery in adjacent coastal and estuarine areas, and the broader fish community from a freshwater lagoon. These findings highlight the importance of the floodplain in supporting the production of large fishes in spite of the episodic nature and relatively short duration of inundation compared to large river floodplains of humid tropical regions. They also illustrate the high degree of food web connectivity mediated by mobile fish in this system in the absence of human modification, and point to the potential consequences of water resource development that may reduce or eliminate hydrological connectivity between the river and its floodplain.
We present some of the first analyses of the stable isotopic composition of dissolved silicon (Si) in groundwater. The groundwater samples were from the Navajo Sandstone aquifer at Black Mesa, ...Arizona, USA, and the Si isotope composition of detrital feldspars and secondary clay coatings in the aquifer were also analyzed. Silicon isotope compositions were measured using high-resolution multi-collector inductively coupled mass spectrometry (HR-MC-ICP-MS) (Nu1700 & NuPlasma HR). The quartz dominated bulk rock and feldspar separates have similar
δ
30Si of −0.09
±
0.04‰ and −0.15
±
0.04‰ (±95% SEM), respectively, and clay separates are isotopically lighter by up to 0.4‰ compared to the feldspars. From isotopic mass-balance considerations, co-existing aqueous fluids should have
δ
30Si values heavier than the primary silicates. Positive
δ
30Si values were only found in the shallow aquifer, where Si isotopes are most likely fractionated during the dissolution of feldspars and subsequent formation of clay minerals. However,
δ
30Si decreases along the flow path from 0.56‰ to −1.42‰, representing the most negative dissolved Si isotope composition so far found for natural waters. We speculate that the enrichment in
28Si is due to dissolution of partly secondary clay minerals and low-temperature silcretes in the Navajo Sandstone. The discovery of the large range and systematic shifts of
δ
30Si values along a groundwater flow path illustrates the potential utility of stable Si isotopes for deciphering the Si cycling in sedimentary basins, tracing fluid flow, and evaluating global Si cycle.
This study presents silicon isotope data for rivers and groundwater from the Bengal Basin. Variations of Si isotope ratios were analyzed by means of high-resolution MC-ICP-MS using a NuPlasma HR. The ...rivers show typical positive
δ
30Si values between 1.3 and 1.7‰, whereas the groundwater samples show decreasing
δ
30Si values from 1.3‰ in shallow groundwater to − 0.2‰ in the deeper groundwater. Beside a very distinctive isotope composition, the concentration of dissolved Si in these groundwater samples is 2–3 times higher than in river samples taken during dry season. The resulting Si flux by groundwater (9.3
×
10
10 mol yr
−
1
) is on the order of the combined Ganges–Brahmaputra Si fluxes, and equals 40% of the total (river
+
groundwater) annual Si flux into the Bay of Bengal. Given the significant large flux and distinctive isotope composition means that the overall isotopic input into the ocean is different from riverine values. However, a sound knowledge of all inputs into the ocean and of how these inputs might vary throughout time is mandatory, in order to correctly interpret palaeo-records of
δ
30Si variations as recorded in sedimentary diatom opal from the last glacial maximum. We extrapolate our results from the Bengal Basin onto a global scale and assess the ocean's sensitivity to changes in inputs, as triggered by large-scale events, such as glaciation periods, where the hydrological cycle might be out of steady state due to the build-up of large continental ice-shields. In such a glaciation scenario, riverine vs. groundwater inputs can be shifted, favoring isotopically lighter groundwater over heavier river inputs into the ocean. The model proves impossible to change the biogenic output to a significant degree, on time scales of a few thousand years, by just changing the isotope inputs into the ocean.
Transmission of cellular identity relies on the faithful transfer of information from the mother to the daughter cell. This process includes accurate replication of the DNA, but also the correct ...propagation of regulatory programs responsible for cellular identity. Errors in DNA replication (mutations) and protein conformation (prions) can trigger stable phenotypic changes and cause human disease, yet the ability of transient transcriptional errors to produce heritable phenotypic change ('epimutations') remains an open question. Here, we demonstrate that transcriptional errors made specifically in the mRNA encoding a transcription factor can promote heritable phenotypic change by reprogramming a transcriptional network, without altering DNA. We have harnessed the classical bistable switch in the lac operon, a memory-module, to capture the consequences of transient transcription errors in living Escherichia coli cells. We engineered an error-prone transcription sequence (A9 run) in the gene encoding the lac repressor and show that this 'slippery' sequence directly increases epigenetic switching, not mutation in the cell population. Therefore, one altered transcript within a multi-generational series of many error-free transcripts can cause long-term phenotypic consequences. Thus, like DNA mutations, transcriptional epimutations can instigate heritable changes that increase phenotypic diversity, which drives both evolution and disease.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Over the course of its 16 m.y. history, the Yellowstone hotspot has produced silicic magmas exhibiting systematic, and often sympathetic, variations in isotopic and chemical composition, temperature ...and frequency of eruption. Nd and Hf isotopic ratios vary systematically from initial eruptions at ∼
16 Ma, contemporaneous with basaltic volcanism in eastern Oregon and Washington, to the present day Yellowstone Volcanic Plateau. Nd and Hf isotopic ratios co-vary and span the range of most terrestrial samples, reflecting mixing of mantle and crustal sources. Earliest erupted silicic magmas were hot (in excess of 1050 °C), relatively less evolved and have isotopic ratios within the range of contemporaneous Columbia River flood basalts. The transit of the hotspot across the lithospheric boundary between the western accreted oceanic terrain and the Precambrian craton at 15 Ma is marked by shifts in
ε
Nd from +
4 to −
11 and in
ε
Hf from +
10 to −
10. The duration of the transit yields a crustal magma source diameter of ∼
70 km. In the interval from 14 to 9 Ma,
ε
Nd systematically increases from −
11 to −
7, recording a minimum increase in the mantle component from 5% to 30%. The mantle component could be twice as great, depending upon the isotopic composition of crust and mantle reservoirs. In this same interval, peak temperatures of ∼
1000 °C occurred at 9 Ma. The last 8 m.y. are characterized by less frequent eruption of lower temperature (830–900 °C) and more compositionally evolved magmas.
Actively dividing cells perform robust and accurate DNA replication during fluctuating nutrient availability, yet factors that prevent disruption of replication remain largely unknown. Here we report ...that DksA, a nutrient-responsive transcription factor, ensures replication completion in
Escherichia coli by removing transcription roadblocks. In the absence of DksA, replication is rapidly arrested upon amino acid starvation. This arrest requires active transcription and is alleviated by RNA polymerase mutants that compensate for DksA activity. This replication arrest occurs independently of exogenous DNA damage, yet it induces the DNA-damage response and recruits the main recombination protein RecA. This function of DksA is independent of its transcription initiation activity but requires its less-studied transcription elongation activity. Finally, GreA/B elongation factors also prevent replication arrest during nutrient stress. We conclude that transcription elongation factors alleviate fundamental conflicts between replication and transcription, thereby protecting replication fork progression and DNA integrity.
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E. coli transcription elongation factors resolve replication-transcription conflicts ► DksA functions in transcription elongation in addition to its role in initiation ► Nutritional stress promotes DNA replication-transcription conflicts ► Replication-transcription conflicts contribute to endogenous DNA damage
Human cancer classification is currently based on the idea of cell of origin, light and electron microscopic attributes of the cancer. What is not yet integrated into cancer classification are the ...functional attributes of these cancer cells. Recent innovative techniques in biology have provided a wealth of information on the genomic, transcriptomic and proteomic changes in cancer cells. The emergence of the concept of cancer stem cells needs to be included in a classification model to capture the known attributes of cancer stem cells and their potential contribution to treatment response, and metastases. The integrated model of cancer classification presented here incorporates all morphology, cancer stem cell contributions, genetic, and functional attributes of cancer. Integrated cancer classification models could eliminate the unclassifiable cancers as used in current classifications. Future cancer treatment may be advanced by using an integrated model of cancer classification.
IntroductionThis study will test the effectiveness of FIT Families (FIT), a multicomponent family-based behavioural intervention, against a credible attention control condition, Home-Based Family ...Support (HBFS). This protocol paper describes the design of a randomised clinical trial testing the efficacy of the FIT intervention. The protocol will assess the efficacy of FIT to improve health status in African American adolescents with obesity (AAAO) and their primary caregivers on primary (percent body fat) and secondary (physical activity, metabolic control, weight loss) outcomes and its cost-effectiveness.Methods180 youth/caregiver dyads are randomised into FIT or HBFS, stratified by age, gender and baseline per cent overweight. The proposed study follows a two condition (FIT, HBFS) by four assessment time points. Tests will be conducted to identify potential relationship of baseline demographic and clinical variables to our dependent variables and see whether they are balanced between groups. It is hypothesised that youth/caregiver dyads randomised to FIT will show significantly greater reductions in percent body fat over a 12-month follow-up period compared with AAAO receiving HBFS. Preliminary findings are expected by November 2023.EthicsThis protocol received IRB approval from the Medical University of South Carolina (Pro00106021; see ‘MUSC IRB 106021 Main Approval.doxc’ in online supplemental materials).DisseminationDissemination activities will include summary documents designed for distribution to the broader medical community/family audience and submission of manuscripts, based on study results, to relevant peer-reviewed scientific high-impact journals.Trial registration numberNCT04974554.
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