Visualization of early chromosome condensation: a hierarchical folding, axial glue model of chromosome structure

Current models of mitotic chromosome structure are based largely on the examination of maximally condensed metaphase chromosomes. Here, we test these models by correlating the distribution of two scaffold components with the appearance of prophase chromosome folding intermediates. We confirm an axial distribution of topoisomerase IIα and the condensin subunit, structural maintenance of chromosomes 2 (SMC2), in unextracted metaphase chromosomes, with SMC2 localizing to a 150–200-nm-diameter central core. In contrast to predictions of radial loop/scaffold models, this axial distribution does not appear until late prophase, after formation of uniformly condensed middle prophase chromosomes. Instead, SMC2 associates throughout early and middle prophase chromatids, frequently forming foci over the chromosome exterior. Early prophase condensation occurs through folding of large-scale chromatin fibers into condensed masses. These resolve into linear, 200–300-nm-diameter middle prophase chromatids that double in diameter by late prophase. We propose a unified model of chromosome structure in which hierarchical levels of chromatin folding are stabilized late in mitosis by an axial “glue.

Memorial heritage and social memory of youth of Eurasian integration countries

Based on the results of a sociological study, the article attempts a narrative explication of the attitudes of young people in Armenia, Belarus, Kazakhstan, Kyrgyzstan, Moldova, Tajikistan, and Russia toward their shared memorial heritage in the context of the permanent reinterpretation of the Soviet past in the former Soviet republics which appears important in the context of the ongoing search for new forms of economic and political integration in the Eurasian space. The study allows providing a characteristic of the place of the Soviet memorial heritage, especially that dedicated to the participation of the USSR in World War II, in the social memory of young people as a unifying factor of millennial and post-millennial generations of the former Soviet republics – participants in Eurasian integration which can contribute to the successful implementation of integration projects in the post-Soviet space. The post-memory generation is generally in favor of preserving the Soviet toponymic names of city streets and squares but young people in countries with a greater degree of linguistic and ethnocultural differences support renaming practices more often. At the same time, the authors note the ambivalence of young people’s attitudes towards the future of memorialization policies in their countries which preserves the possibility of potential revision and reconsideration of the Soviet past in the future.

Are There Common Mechanisms Between the Hutchinson–Gilford Progeria Syndrome and Natural Aging?

The Hutchinson–Gilford progeria syndrome (HGPS) is a premature aging disease caused by mutations of the LMNA gene leading to increased production of a partially processed form of the nuclear fibrillar protein lamin A – progerin. Progerin acts as a dominant factor that leads to multiple morphological anomalies of cell nuclei and disturbances in heterochromatin organization, mitosis, DNA replication and repair, and gene transcription. Progerin-positive cells are present in primary fibroblast cultures obtained from the skin of normal donors at advanced ages. These cells display HGPS-like defects in nuclear morphology, decreased H3K9me3 and HP1, and increased histone H2AX phosphorylation marks of the DNA damage loci. Inhibition of progerin production in cells of aged non-HGPS donors in vivo increases the proliferative activity, H3K9me3, and HP1, and decreases the senescence markers p21, IGFBP3, and GADD45B to the levels of young donor cells. Thus, progerin-dependent mechanisms act in natural aging. Excessive activity of the same mechanisms may well be the cause of premature aging in HGPS. Telomere attrition is widely regarded to be one of the primary hallmarks of aging. Progerin expression in normal human fibroblasts accelerates the loss of telomeres. Changes in lamina organization may directly affect telomere attrition resulting in accelerated replicative senescence and progeroid phenotypes. The chronological aging in normal individuals and the premature aging in HGPS patients are mediated by similar changes in the activity of signaling pathways, including downregulation of DNA repair and chromatin organization, and upregulation of ERK, mTOR, GH-IGF1, MAPK, TGFβ, and mitochondrial dysfunction. Multiple epigenetic changes are common to premature aging in HGPS and natural aging. Recent studies showed that epigenetic systems could play an active role as drivers of both forms of aging. It may be suggested that these systems translate the effects of various internal and external factors into universal molecular hallmarks, largely common between natural and accelerated forms of aging. Drugs acting at both natural aging and HGPS are likely to exist. For example, vitamin D3 reduces the progerin production and alleviates most HGPS features, and also slows down epigenetic aging in overweight and obese non-HGPS individuals with suboptimal vitamin D status

Solid state synthesis of carbon-encapsulated iron carbide nanoparticles and their interaction with living cells †

Superparamagnetic carbon-encapsulated iron carbide nanoparticles (NPs), Fe 7 C 3 @C, with unique properties, were produced from pure ferrocene by high pressure-high temperature synthesis. These NPs combine the merits of nanodiamonds and SPIONs but lack their shortcomings which limit their use for biomedical applications. Investigation of these NPs by X-ray diffraction, electron microscopy techniques, X-ray spectroscopic and magnetic measurement methods has demonstrated that this method of synthesis yields NPs with perfectly controllable physical properties. Using magnetic and subsequent fractional separation of magnetic NPs from residual carbon, the aqueous suspensions of Fe 7 C 3 @C NPs with an average particle size of $25 nm were prepared. The suspensions were used for in vitro studies of the interaction of Fe 7 C 3 @C NPs with cultured mammalian cells. The dynamics of interaction of the living cells with Fe 7 C 3 @C was studied by optical microscopy using time-lapse video recording and also by transmission electron microscopy. Using novel highly sensitive cytotoxicity tests based on the cell proliferation assay and long-term live cell observations it was shown that the internalization of Fe 7 C 3 @C NPs has no cytotoxic effect on cultured cells and does not interfere with the process of their mitotic division, a fundamental property that ensures the existence of living organisms. The influence of NPs on the proliferative activity of cultured cells was not detected as well. These results indicate that the carbon capsules of Fe 7 C 3 @C NPs are air-tight which could offer great opportunities for future use of these superparamagnetic NPs in biology and medicine

Large-scale chromatin structure of inducible genes: transcription on a condensed, linear template

The structure of interphase chromosomes, and in particular the changes in large-scale chromatin structure accompanying transcriptional activation, remain poorly characterized. Here we use light microscopy and in vivo immunogold labeling to directly visualize the interphase chromosome conformation of 1–2 Mbp chromatin domains formed by multi-copy BAC transgenes containing 130–220 kb of genomic DNA surrounding the DHFR, Hsp70, or MT gene loci. We demonstrate near-endogenous transcription levels in the context of large-scale chromatin fibers compacted nonuniformly well above the 30-nm chromatin fiber. An approximately 1.5–3-fold extension of these large-scale chromatin fibers accompanies transcriptional induction and active genes remain mobile. Heat shock–induced Hsp70 transgenes associate with the exterior of nuclear speckles, with Hsp70 transcripts accumulating within the speckle. Live-cell imaging reveals distinct dynamic events, with Hsp70 transgenes associating with adjacent speckles, nucleating new speckles, or moving to preexisting speckles. Our results call for reexamination of classical models of interphase chromosome organization

Mechanisms of increased mitochondria-dependent necrosis in Wiskott-Aldrich syndrome platelets

Wiskott-Aldrich syndrome (WAS) is associated with thrombocytopenia of unclear origin. We investigated real-time cytosolic calcium dynamics, mitochondrial membrane potential and phoszphatidylserine (PS) exposure in single fibrinogen-bound platelets using confocal microscopy. The WAS platelets had higher resting calcium levels, more frequent spikes, and their mitochondria more frequently lost membrane potential followed by PS exposure (in 22.9% of platelets vs. 3.9% in controls;

The Xenopus laevis centrosome aurora/Ipl1-related kinase.

International audienceThe cDNA encoding the protein kinase pEg2 was originally cloned through a differential screening performed during the early development of Xenopus laevis. pEg2 orthologues were found in various organisms and were classified in a new family of oncogenic mitotic protein kinases named 'aurora/Ipl1-related kinases' after the Drosophila melanogaster gene aurora and the Saccharomyces cerevisiae gene Ipl1. The catalytic activity of pEg2 is necessary for the mitotic microtubule spindle formation in Xenopus laevis egg extracts. The addition of a dominant negative form of pEg2 to in vitro spindle assembly assays leads to monopolar spindles generated by a defect of centrosome separation. In Xenopus cultured cells, pEg2 was confined around the pericentriolar material once centrosomes were duplicated. The centrosome localization does not depend on the presence of microtubules. However, in vitro, the protein binds to taxol-stabilized microtubules independently of its kinase activity. During mitosis the location of the protein changes, in metaphase the kinase localizes on the microtubules at the poles of the mitotic spindle whereas it is not present on astral microtubules. This localization persists until the segregation of the chromosomes is completed. The presence of the kinase on the spindle may reveal another yet unknown function

Distribution of XCAP-E and XCAP-D2 in the Xenopus oocyte nucleus.

International audienceSeveral antibodies were used to examine the distribution of two condensin members, XCAP-E and XCAP-D2, in the nucleus of Xenopus oocytes. XCAP-D2 was found to be associated with the lampbrush chromosomes. The chromosomal regions containing XCAP-D2 correspond precisely to domains of highly compacted chromatin, suggesting a direct contribution of XCAP-D2 in meiotic chromatin organization. In contrast, XCAP-E was found to be absent from chromosomes but was detected at a high concentration in the granular component of nucleoli. The subnucleolar localization of XCAP-E was further confirmed by double labeling using several nucleolar protein markers. The fate of nucleolar XCAP-E was also followed when changes in the nucleoli morphology were artificially induced. The apparent exclusion of XCAP-E from the ribosomal DNA and its tight association with the granular component in all preparations suggest that it might be sequestrated in nucleoli during early stages of meiosis. Interestingly, both XCAP-D2 and XCAP-E were also detected in Cajal bodies, which are organelles suspected to play a role in the assembly/modification of the RNA transcription and processing machinery. The presence of two condensins in CBs might extend such a role of assembly to chromatin macromolecular components as well

Ballistic energy transport in PEG oligomers

Energy transport between the terminal groups of the azido-PEG-succinimide ester compounds with a number of repeating PEG units of 0, 4, 8, and 12 was studied using relaxation-assisted two-dimensional infrared spectroscopy. The through-bond energy transport time, evaluated as the waiting time at which the cross peak maximum is reached, Tmax, was found to be linearly dependent on the chain length for chain lengths up to 60 Å suggesting a ballistic energy transport regime. The through-bond energy transport speed is found to be ca. 500 m/s. The cross-peak amplitude at the maximum decays exponentially with the chain length with a characteristic decay distance of 15.7 ± 1 Å. Substantial mode delocalization across the PEG bridge is found, which can support the energy propagation as a wavepacket