Activation of M-phase-specific histone H1 kinase by modification of the phosphorylation of its p34cdc2 and cyclin components

An M-phase-specific histone H1 kinase (H1K) has been described in a wide variety of eukaryotic cell types undergoing the G2/M transition in the cell division cycle. We have used p13suc1-Sepharose affinity chromatography to purify H1K to near homogeneity from matured starfish oocytes. A yield of 67% was obtained. Active H1K behaves as a 90- to 100-kD protein and appears to be constituted of equimolar amounts of cyclin and p34cdc2. The p34cdc2 subunit becomes tyrosine-dephosphorylated as the H1K is activated during entry of the oocytes into M phase, whereas the cyclin subunit is reciprocally phosphorylated. Acid phosphatase treatment of inactive p34cdc2/cyclin complex induces p34cdc2 dephosphorylation and three- to eightfold stimulation of the enzyme activity. These results suggest that active M-phase-specific H1K is constituted of both dephosphorylated p34cdc2 and phosphorylated cyclin

Les technologies numériques, une innovation pédagogique ? : éditorial

International audienceLes auteurs (par ailleurs coordinateurs de ce dossier) questionnent les motifs de ce qui apparaît comme un engouement, voire une fascination, à l’égard des technologies numériques, que la digitalisation de la formation soit considérée comme souhaitable ou inéluctable. Ils explorent le rapport au numérique en formation sous trois angles. D’abord comme rapport à la technique et témoignant d’une conception déterministe des techniques (ils reviennent sur l’emploi des expressions « techniques pédagogiques » et « technologies numériques » et sur leurs différentes acceptions. Ils soulignent combien l’ambiguïté dans l’usage de ces notions facilite la confusion entre innovation technologique et innovation pédagogique, confusion elle-même entretenue par une approche déterministe des techniques. Prenant appui sur plusieurs articles présentés dans ce dossier, ils invitent également à considérer le rapport au numérique comme témoignant d’une approche gestionnaire de la formation et d’une mise à l’écart des questions pédagogiques. Enfin, ils invitent à penser autrement le rapport au numérique, selon une approche « phénoménologique », en considérant la façon dont ce changement de « système technique » reconfigure la façon de percevoir le monde et donc, nécessairement, les modes de conception et d’organisation des situations d’apprentissage

Substituent effect in unsymmetrical lutetium bisphthalocyanines: a DFT analysis

International audienceDFT calculations have been carried out on a series of unsymmetrical bisphthalocyanine lutetium complexes in which one of the ligands is substituted by 8 or 16 chlorine atoms. It is shown that their unpaired electron is predominantly localized on the non-substituted ligand. An orbital explanation is provided to rationalize this effect. A good agreement is found between the computed and experimental ionization potentials and electroaffinities and the redox potentials of a closely related series, as well as between their TDDFT-computed and experimental UV-visible transitions which are analysed

Description of the biogeochemical features of the subtropical southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer of the International Polar Year

International audienceMeridional and vertical distributions of several biogeochemical parameters were studied along a section in the southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer 2008 of the International Polar Year to characterize the biogeochemical provinces and to assess the seasonal net diatom production. Based on analyses of macro-nutrients, ammonium (NH4), chlorophyll a, (Chl a), phaeopigments, biogenic silica (BSi), particulate inorganic carbon (PIC), and particulate organic carbon and nitrogen (POC and PON, respectively), four biogeochemical domains were distinguished along the section: the subtropical Atlantic, the confluence zone of the subtropical and subantarctic domains, the Polar Frontal Zone (PFZ) in the Antarctic Circumpolar Current (ACC), and the north-eastern branch of the Weddell Gyre. The subtropical region displayed extremely low nutrient concentrations featuring oligotrophic conditions, and sub-surface maxima of Chl a and phaeopigments never exceeded 0.5 µg L−1 and 0.25 µg L−1, respectively. The anticyclonic and cyclonic eddies crossed in the Cape Basin were characterized by a deepening and a rise, respectively, of the nutrients isoclines. The confluence zone of the subtropical domain and the northern side of the ACC within the subantarctic domain displayed remnant nitrate and phosphate levels, whereas silicate concentrations kept to extremely low levels. In this area, Chl a level of 0.4-0.5 µg L−1 distributed homogenously within the mixed layer, and POC and PON accumulated to values up to 10 µM and 1.5 µM, respectively, indicative of biomass accumulation along the confluence zone during the late productive period. In the ACC domain, the Polar Frontal Zone was marked by a post-bloom of diatoms that extended beyond the Polar Front (PF) during this late summer condition, as primarily evidenced by the massive depletion of silicic acid in the surface waters. The accumulation of NH4 to values up to 1.25 µM at 100 m depth centred on the PF and the accumulation of BSi up to 0.5 µM in the surface waters of the central part of the PFZ also featured a late stage of the seasonal diatom bloom. The silica daily net production rate based on the seasonal depletion of silicic acid was estimated to be 11.9 ± 6.5 mmol m−2 d−1 in the domain of the vast diatom post-bloom, agreeing well with the previously recorded values in this province. The Weddell Gyre occasionally displayed relative surface depletion of silicic acid, suggesting a late stage of a relatively minor diatom bloom possibly driven by iceberg drifting releases of iron. In this domain the estimated range of silica daily net production rate (e.g. 21.1 ± 8.8 mmol m−2 d−1) is consistent with previous studies, but was not significantly higher than that in the Polar Front region

Parameter identification of 42CrMo4 steel hot forging plastic flow behaviour using industrial upsetting presses and finite element simulations

An experimental-numerical methodology was proposed for the parameter identification of constitutive laws, when applied to hot forging. Industrial presses were directly used to generate the reference experiments for identification. The strain and temperature heterogeneity that appears during on-press compression experiments was taken into account by an FE-based inverse method. Specific experiments were designed for the identification of the heat transfer and friction coefficients. A testing tool was designed and instrumented with displacement sensors and a force cell. This was then used on a hydraulic press and a screw press in order to cover a large range of strain rates. The identified parameter set was validated with respect to specialized plastometers, and a semi industrial validation forging process. A reasonable accuracy was observed, particularly in realistic forging condition

Sea ice thickness and elastic properties from the analysis of multimodal guided wave propagation measured with a passive seismic array

Field data are needed for a better understanding of sea ice decline in the context of climate change. The rapid technological and methodological advances of the last decade have led to a reconsideration of seismic methods in this matter. In particular, passive seismology has filled an important gap by removing the need to use active sources. We present a seismic experiment where an array of 247 geophones was deployed on sea ice, in the Van Mijen fjord near Sveagruva (Svalbard). The array is a mix of 1C and 3C stations with sampling frequencies of 500 and 1000 Hz. They recorded continuously the ambient seismic field in sea ice between 28 February and 26 March 2019. Data also include active acquisitions on 1 and 26 March with a radar antenna, a shaker unit, impulsive sources, and artificial sources of seismic noise. This data set is of unprecedented quality regarding sea ice seismic monitoring, as it also includes thousands of microseismic events recorded each day. By combining passive seismology approaches with specific array processing methods, we demonstrate that the multimodal dispersion curves of sea ice can be calculated without an active source and then used to infer sea ice properties. We calculated an ice thickness, Young's modulus, and Poisson's ratio with values h=543 cm, E=3.90.15 GPa, and nu=0.340.02 on 1 March, and h=583 cm, E=4.4 +/- 0.15 GPa, and nu=0.32 +/- 0.02 on 5 March. These values are consistent with in situ field measurements and observations.Peer reviewe

What causes the inverse relationship between primary production and export efficiency in the Southern Ocean?

The ocean contributes to regulating atmospheric CO2 levels, partly via variability in the fraction of primary production (PP) which is exported out of the surface layer (i.e. the e-ratio). Southern Ocean studies have found that, contrary to global scale analyses, an inverse relationship exists between e-ratio and PP. This relationship remains unexplained, with potential hypotheses being i) large export of dissolved organic carbon (DOC) in high PP areas, ii) strong surface microbial recycling in high PP regions and/ or iii) grazing mediated export varies inversely with PP. We find that the export of DOC has a limited influence in setting the negative e-ratio/PP relationship. However, we observed that at sites with low PP and high e-ratios, zooplankton mediated export is large and surface microbial abundance low suggesting that both are important drivers of the magnitude of the e-ratio in the Southern Ocean

Sea ice diatom contributions to Holocene nutrient utilization in East Antarctica

Combined high-resolution Holocene δ30Sidiat and δ13Cdiat paleorecords are presented from theSeasonal Ice Zone, East Antarctica. Both data sets reflect periods of increased nutrient utilization by diatomsduring the Hypsithermal period (circa 7800 to 3500 calendar years (cal years) B.P.), coincident with a higherabundance of open water diatom species (Fragilariopsis kerguelensis), increased biogenic silica productivity(%BSi), and higher regional summer temperatures. The Neoglacial period (after circa 3500 cal years B.P.) isreflected by an increase in sea ice indicative species (Fragilariopsis curta and Fragilariopsis cylindrus,upto50%) along with a decrease in %BSi and δ13Cdiat(< 18‰ to 23‰). However, over this period, δ30Sidiatdata show an increasing trend, to some of the highest values in the Holocene record (average of +0.43‰).Competing hypotheses are discussed to account for the decoupling trend in utilization proxies including ironfertilization, species-dependent fractionation effects, and diatom habitats. Based on mass balance calculations,we highlight that diatom species derived from the semi-enclosed sea ice environment may have a confoundingeffect upon δ30Sidowncorecompositions of the seasonal sea ice zone. A diatom composition, with approximately28% of biogenic silica derived from the sea ice environment (diat-SI) can account for the increased averagecompo sition of δ30Sidiatduring the Neoglacial. These data highlight the significant role sea ice diatoms can playwith relation to their export in sediment records, which has implications on productivity reconstructions fromthe seasonal ice zone

Comparing glacial and Holocene opal fluxes in the Pacific sector of the Southern Ocean

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 24 (2009): PA2214, doi:10.1029/2008PA001693.The silicic acid leakage hypothesis (SALH) predicts that during glacial periods excess silicic acid was transported from the Southern Ocean to lower latitudes, which favored diatom production over coccolithophorid production and caused a drawdown of atmospheric CO2. Downcore records of 230Th-normalized opal (biogenic silica) fluxes from 31 cores in the Pacific sector of the Southern Ocean were used to compare diatom productivity during the last glacial period to that of the Holocene and to examine the evidence for increased glacial Si export to the tropics. Average glacial opal fluxes south of the modern Antarctic Polar Front (APF) were less than during the Holocene, while average glacial opal fluxes north of the APF were greater than during the Holocene. However, the magnitude of the increase north of the APF was not enough to offset decreased fluxes to the south, resulting in a decrease in opal burial in the Pacific sector of the Southern Ocean during the last glacial period, equivalent to approximately 15 Gt opal ka−1. This is consistent with the work of Chase et al. (2003a), and satisfies the primary requirement of the SALH, assuming that the upwelled supply of Si was approximately equivalent during the Holocene and the glacial period. However, previous results from the equatorial oceans are inconsistent with the other predictions of the SALH, namely that either the Corg:CaCO3 ratio or the rate of opal burial should have increased during glacial periods. We compare the magnitudes of changes in the Southern Ocean and the tropics and suggest that Si escaping the glacial Southern Ocean must have had an alternate destination, possibly the continental margins. There is currently insufficient data to test this hypothesis, but the existence of this sink and its potential impact on glacial pCO2 remain interesting topics for future study.Funding for this research was provided in part by the U.S. NSF (grant OPP02-30268). We thank the core repository at LDEO and the Antarctic Research Facility at FSU for providing samples