Compartimentalized control of Cdk1 drives mitotic spindle assembly

During cell division, dramatic microtubular rearrangements driven by cyclin B-cdk1 (Cdk1) kinase activity mark mitosis onset leading to interphase cytoskeleton dissolution and mitotic spindle assembly. Once activated by Cdc25, that reverses inhibitory phosphorylation operated by Wee1/Myt1, Cdk1 clears the cytoplasm from microtubules by inhibiting microtubule associated proteins (MAPs) with microtubule growth-promoting properties. Nevertheless, some of these MAPs are required for spindle assembly, creating quite a conundrum. We show here that a Cdk1 fraction bound to spindle structures escaped Cdc25 action and remained inhibited by phosphorylation (i-Cdk1) in mitotic human cells. Loss or restoration of i-Cdk1 inhibited or promoted spindle assembly, respectively. Furthermore, polymerizing spindle microtubules fostered i-Cdk1 by aggregating with Wee1 and excluding Cdc25. Our data reveal that spindle assembly relies on compartimentalized control of Cdk1 activity.

Stellar splashback: the edge of the intracluster light

ABSTRACT We examine the outskirts of galaxy clusters in the C-EAGLE simulations to quantify the ‘edges’ of the stellar and dark matter distribution. The radius of the steepest slope in the dark matter, commonly used as a proxy for the splashback radius, is located at $\sim \, r_{200 \rm m}$; the strength and location of this feature depends on the recent mass accretion rate, in good agreement with previous work. Interestingly, the stellar distribution (or intracluster light, ICL) also has a well-defined edge, which is directly related to the splashback radius of the halo. Thus, detecting the edge of the ICL can provide an independent measure of the physical boundary of the halo, and the recent mass accretion rate. We show that these caustics can also be seen in the projected density profiles, but care must be taken to account for the influence of substructures and other non-diffuse material, which can bias and/or weaken the signal of the steepest slope. This is particularly important for the stellar material, which has a higher fraction bound in subhaloes than the dark matter. Finally, we show that the ‘stellar splashback’ feature is located beyond current observational constraints on the ICL, but these large projected distances (≫1 Mpc) and low surface brightnesses (μ ≫ 32 mag arcsec−2) can be reached with upcoming observational facilities such as the Vera C. Rubin Observatory, the Nancy Grace Roman Space Telescope, and Euclid.

Sequential extraction procedure for fractionation of Pb and Cr in artificial and contaminated soil

Metal contamination of soil is due to mining, manufacturing and use of synthetic products (e.g. pesticides, paints, batteries, industrial waste and industrial or domestic sludge) which is a serious environmental problem. Hence, determining chemical forms of metals in soils is important to evaluate their mobility or bioavailability. Both artificial and contaminated soils were sequentially extracted to fractionate metals into the water soluble fraction (WSF), exchangeable fraction (EF), bound to carbonate fraction, bound to metal oxide fraction, organically bound fraction (OBF) and residual fraction (RF). In the case of contaminated soil, Pb and Cr are found to be associated with the carbonate fraction while in artificial soil, Pb bound to WSF and Cr with the Fe/Mn fraction. Chemical properties such as pH, electrical conductivity (EC) and textural classification of concerned soils were also analyzed. Percentage recovery was calculated to check the reliability of processes both in Pb and Cr, and it was found to be more in Cr (66% and 84%) in both artificial and contaminated soil than Pb (5% and 34%) in both soils. Analyses of extracts were carried out by atomic absorption spectrometry (AAS). Results were interpreted in terms of environmental mobility or bioavailability of metals.

Mobility and distribution of barium and strontium in profiles of podzolic soils

The study was aimed at determining the content, distribution and mobility of barium and strontium in various forest podzol soils. Samples with a wide range of chemical and physical properties were collected from typical uncontaminated soils of south-western Poland. The total metal content in the analyzed soils was considered as the geochemical background thanks to the natural features of the study site. Sequential chemical extraction procedure were used to provide information on the mobility and bioavailability of the studied metals in the soil. Fractions of Ba and Sr were determined using the five-step procedure of Tessier et al. (1979). The results show that heavy metals were generally represented by the exchangeable fraction (F1 . barium) and the residual fraction (F5 . strontium) with the average values at 53 and 69%, respectively. The mobility of barium in all soil profiles was very high, ranging within 52.54% and indicating a generally high availability and mobility. Relatively very low levels of the trace elements were found in the fraction bound to organic matter (F4: 3.8%). Very low levels of strontium were found also in the fraction bound to carbonates (F2: 2.3%). Humic-eluvial, illuvial and sideric horizons were enriched in the fractions of barium and strontium bound to iron and manganese oxides (F3).

Fractionation of Selected Heavy Metals in Agricultural Soils / Frakcjonowanie Wybranych Metali Ciężkich W Glebach Uprawnych

The content of trace elements in soils varies widely and their mobility and availability depends not only on the total content but also on the form of in which these elements occur. The aim of this study was to determine the total content of nickel, lead, zinc and copper in soils used for agriculture, and assess the mobility and phytoavailability of these metals against a background of physical and chemical properties of these soils. In samples taken from three soil profiles (Phaeozem and 2 Fluvisols) the contents of Ni, Pb, Zn and Cu were determined using atomic absorption spectroscopy in the solutions obtained according to the protocol of modified BCR sequential extraction procedure supplemented with aqua regia digestion. The total content of the analyzed metals in most cases corresponded to the natural values, often not exceeding the geochemical background level. It was only in the one profile of the Fluvisols (Endogleyic Fluvisol) that a higher concentration of zinc and lead was noticed (especially in the surface horizon), slightly exceeding the legal limit. Among the studied metals the lowest phytoavailability was characterized by copper (exchangeable forms on average 4.73% of the total), and the highest by zinc (11.49%). Nickel was the most permanently bound with soil solid phase, and its content in the residual fraction reached 84.46% of the total. Approximately a half of the total lead content was determined as a fraction bound with iron and manganese oxides, while in the case of this metal a significant role in binding of this metal was playing organic matter (fraction bound with organic matter and sulphides - an average of 27.5%). Significant role in the binding of all investigated metals was credited to iron and manganese compounds.

Behavior and Distribution of Heavy Metals Including Rare Earth Elements, Thorium, and Uranium in Sludge from Industry Water Treatment Plant and Recovery Method of Metals by Biosurfactants Application

In order to investigate the behavior, distribution, and characteristics of heavy metals including rare earth elements (REEs), thorium (Th), and uranium (U) in sludge, the total and fractional concentrations of these elements in sludge collected from an industry water treatment plant were determined and compared with those in natural soil. In addition, the removal/recovery process of heavy metals (Pb, Cr, and Ni) from the polluted sludge was studied with biosurfactant (saponin and sophorolipid) elution by batch and column experiments to evaluate the efficiency of biosurfactant for the removal of heavy metals. Consequently, the following matters have been largely clarified. (1) Heavy metallic elements in sludge have generally larger concentrations and exist as more unstable fraction than those in natural soil. (2) Nonionic saponin including carboxyl group is more efficient than sophorolipid for the removal of heavy metals in polluted sludge. Saponin has selectivity for the mobilization of heavy metals and mainly reacts with heavy metals in F3 (the fraction bound to carbonates) and F5 (the fraction bound to Fe-Mn oxides). (3) The recovery efficiency of heavy metals (Pb, Ni, and Cr) reached about 90–100% using a precipitation method with alkaline solution.

Calnexin and BiP act as sequential molecular chaperones during thyroglobulin folding in the endoplasmic reticulum.

Before secretion, newly synthesized thyroglobulin (Tg) folds via a series of intermediates: disulfide-linked aggregates and unfolded monomers-->folded monomers-->dimers. Immediately after synthesis, very little Tg associated with calnexin (a membrane-bound molecular chaperone in the ER), while a larger fraction bound BiP (a lumenal ER chaperone); dissociation from these chaperones showed superficially similar kinetics. Calnexin might bind selectively to carbohydrates within glycoproteins, or to hydrophobic surfaces of secretory proteins while they form proper disulfide bonds (Wada, I., W.-J. Ou, M.-C. Liu, and G. Scheele, J. Biol. Chem. 1994. 269:7464-7472). Because Tg has multiple disulfides, as well as glycans, we tested a brief exposure of live thyrocytes to dithiothreitol, which resulted in quantitative aggregation of nascent Tg, as analyzed by SDS-PAGE of cells lysed without further reduction. Cells lysed in the presence of dithiothreitol under non-denaturing conditions caused Tg aggregates to run as reduced monomers. For cells lysed either way, after in vivo reduction, Tg coprecipitated with calnexin. After washout of dithiothreitol, nascent Tg aggregates dissolved intracellularly and were secreted ultimately. 1 h after washout, > or = 92% of labeled Tg was found to dissociate from calnexin, while the fraction of labeled Tg bound to BiP rose from 0 to approximately 40%, demonstrating a "precursor-product" relationship. Whereas intralumenal reduction was essential for efficient Tg coprecipitation with calnexin, Tg glycosylation was not required. These data are among the first to demonstrate sequential chaperone function involved in conformational maturation of nascent secretory proteins within the ER.

Species specificity and organ, cellular and subcellular localization of the 100 kDa Ras GTPase activating protein

A p100-GAP isoform, generated by an alternative splicing mechanism that eliminates the 180 hydrophobic amino acids at the amino terminus of p120-GAP, has been described in human placenta, in addition to the known p120GAP and neurofibromin. This p100-GAP possesses full Ras-GTPase stimulating activity. p120-GAP is ubiquitously localized in the cytosol while the localization of p100-GAP is unknown. Here we have explored the precise localization of p100-GAP and show that p100-GAP is present only in extracts of primate placenta. It is abundant in both human and Maccaca Rhesus placentae, where it is present in far larger amounts than p120-GAP. The p100-GAP is species-specific since it was not detected in the placenta of pig, sheep, mouse or rat. p100-GAP was also found to be organ-specific, since it was not detectable in organs other than the placenta. In this connection, we substantiated our previous finding that p100-GAP is mainly localized in the trophoblasts. Both subcellular trophoblast fractionation and immunofluorescence analyses showed that this protein was distributed between the cytosol, plasma membrane and a fraction bound to the nucleus, but not inside it. This highly restrictive specificity of p100-GAP localization in relation to species, organ and cell type, confirms the extreme singularity of this protein, and strongly suggests a particular specific function in the trophoblast.