Reticulon 4a/NogoA locates to regions of high membrane curvature and may have a role in nuclear envelope growth

Reticulon 4a (Rtn4a) is a membrane protein that shapes tubules of the endoplasmic reticulum (ER). The ER is attached to the nuclear envelope (NE) during interphase and has a role in post mitotic/meiotic NE reassembly. We speculated that Rtn4a has a role in NE dynamics. Using immuno-electron microscopy we found that Rtn4a is located at junctions between membranes in the cytoplasm, and between cytoplasmic membranes and the outer nuclear membrane in growing Xenopus oocyte nuclei. We found that during NE assembly in Xenopus egg extracts, Rtn4a localises to the edges of membranes that are flattening onto the chromatin. These results demonstrate that Rtn4a locates to regions of high membrane curvature in the ER and the assembling NE. Previously it was shown that incubation of egg extracts with antibodies against Rtn4a caused ER to form into large vesicles instead of tubules. To test whether Rtn4a contributes to NE assembly, we added the same Rtn4a antibody to nuclear assembly reactions. Chromatin was enclosed by membranes containing nuclear pore complexes, but nuclei did not grow. Instead large sacs of ER membranes attached to, but did not integrate into the NE. It is possible therefore that Rtn4a may have a role in NE assembly.     

Mossbauer spectroscopy of cells of cyanobacteria Synechocystis sp. PCC 6803 devoid of photosystem I and containing inactive phycobilisomes]

Mossbauer spectra of the psaAB mutant of Synechocystis sp. PPC 6803 devoid of photosystem I grown in a 57Fe-containing medium were measured. The spectrum is a broadened doublet whose size (about 20%) and parameters (isomeric shift delta = 0.3 mm/s and quadrupole splitting delta = 0.8 mm/s) suggest the presence of abundant nanoclusters of Fe3+ oxides in a superparamagnetic state tightly bound to the membrane. Treatment of cells with EDTA was accompanied by a substantial (tenfold) decrease in the amount of iron nonspecifically bound to the membrane and the appearance of Fe2+ localized, probably, inside cells and/or cell membranes. In addition, the spectrum of washed cells exhibited superfine magnetic splitting due to iron oxide clusters greater in size than nanoclusters present in the membrane prior to EDTA treatment.     

Cdk1 and okadaic acid-sensitive phosphatases control assembly of nuclear pore complexes in Drosophila embryos

Disassembly and reassembly of the nuclear pore complexes (NPCs) is one of the major events during open mitosis in higher eukaryotes. However, how this process is controlled by the mitotic machinery is not clear. To investigate this we developed a novel in vivo model system based on syncytial Drosophila embryos. We microinjected different mitotic effectors into the embryonic cytoplasm and monitored the dynamics of disassembly/reassembly of NPCs in live embryos using fluorescently labeled wheat germ agglutinin (WGA) or in fixed embryos using electron microscopy and immunostaining techniques. We found that in live embryos Cdk1 activity was necessary and sufficient to induce disassembly of NPCs as well as their cytoplasmic mimics: annulate lamellae pore complexes (ALPCs). Cdk1 activity was also required for keeping NPCs and ALPCs disassembled during mitosis. In agreement recombinant Cdk1/cyclin B was able to induce phosphorylation and dissociation of nucleoporins from the NPCs in vitro. Conversely, reassembly of NPCs and ALPCs was dependent on the activity of protein phosphatases, sensitive to okadaic acid (OA). Our findings suggest a model where mitotic disassembly/reassembly of the NPCs is regulated by a dynamic equilibrium of Cdk1 and OA-sensitive phosphatase activities and provide evidence that mitotic phosphorylation mediates disassembly of the NPC.     

Exogenous allogenic fragmented double-stranded DNA is internalized into human dendritic cells and enhances their allostimulatory activity

Exogenous allogenic DNA as nucleosome-free fragments reaches main cellular compartments (cytoplasm, nucleus) of human dendritic cells and deposits in the nuclear interchromosomal space without visibly changing in linear size. The presence of such allogenic fragmented DNA in medium in which human dendritic cells are cultured produces an enhancement of their allostimulatory activity. This enhancement is comparable to that produced by the standard maturation stimulus lipopolysaccharide Escherichia coli.     

Biosynthesis of phytohormones in algae

Like in the case of higher plants, algal growth and development are controlled by the hormonal regulatory system. Essentially all known phytohormones were identified in various algal taxa, and the range of their physiological activities was confirmed. At the same time, our knowledge of enzymes involved in the phytohormone synthesis in algae is rather limited. Data concerning genes encoding these enzymes are still more fragmentary. Current data about proteomes of some algae allow the revealing of amino acid sequences with homology to those of the higher plant enzymes and their conserved domains.     

Capabilities of digital microfocal x-ray study in the evaluation of reparative regeneration of bone tissue in an experiment

Digital microfocal x-ray study was experimentally studied in animals to examine the time course of changes in their bone regeneration. Sixteen Chinchila rabbits whose bone defect in the angle of the mandibular ramus had been closed with the osteoplastic material Gapcol with the applied allogeneic, autologous stem cells isolated from rabbit adipose tissue and human plasma enriched with thrombocytic growth factors were examined. The capabilities of digital microfocal x-ray study versus x-ray computed tomography were compared in the evaluation of reparative regeneration of bone tissue. The results of radiation studies were verified with the data of scanning electron microscopy.     

Dynamics of the annulate lamellae in Drosophila syncytial embryos

In eukaryotic cells, mitotic events are controlled by evolutionarily conserved cyclin-dependent kinases (cdk): these kinases phosphorylate cell proteins, which causes structural reorganization of the entire cell. Our recent studies of Drosophila syncytial embryos have demonstrated that cdk1 activity is a key factor that controls nuclear pore complex assembly/disassembly and affects the structure of cytoplasmic pores in the annulate. In this paper, we report a comparative analysis of these cytoplasmic organelles throughout the cell-cycle and throughout the development of Drosophila syncytial embryos. Based on the results obtained, it was presupposed that distribution of annulate lamellae containing cytoplasmic pores could reflect the inactivation of the mitotic kinase cdk1 in Drosophila syncytial embryos.     

High temperature initiates changes in Wolbachia ultrastructure in ovaries and early embryos of Drosophila melanogaster

Electron microscopic analysis of Drosophila melanogaster (w1118) ovarian cells has shown that stressful heat treatment of flies causes the appearance of electron-dense granules and large lysosomes in the cytoplasm of ovarian cells. These changes are not due to the presence of the endosymbiotic bacteria Wolbachia, as these changes were observed in both infected and uninfected flies. Essential envelope disturbances and other structural alterations have been revealed in the bacteria present in the ovarian cell cytoplasm of the flies. Some of the fly embryos died after heat shock; however, the bacteria retain their typical morphology in survived embryos. Endosymbionts did not change their localization in ovarian cells and in early fly embryos; they closely interacted with mitochondria and endoplasmic reticulum after the heat-shock treatment of flies. The performed study has shown that the high temperature affects both the host and the endosymbiont, but does not change the character of their structural interaction. Original Russian Text M.V. Zhukova, D.A. Voronin, E.V. Kiseleva, 2008, published in Tsitologiya, vol. 50, No. 5, 2008.     

Differential effects of stretch and compression on membrane currents and [Na]c in ventricular myocytes

Mechano-electrical feedback was studied in the single ventricular myocytes. A small fraction (approximately 10%) of the cell surface could be stretched or compressed by a glass stylus. Stretch depolarised, shortened the action potential and induced extra systoles. Stretch activated non-selective cation currents (I_ns) showed a linear voltage dependence, a reversal potential of 0 mV, a pure cation selectivity, and were blocked by 8 μM Gd³⁺ or 30 μM streptomycin. Stretch reduced Ca²⁺ and K⁺ (I_K) currents. Local compression of broadwise attached cells activated I_K but not I_ns. Cytochalasin D or colchicin, thought to disrupt the cytoskeleton, suppressed the mechanosensitivity of I_ns and I_K. During stretch, the cytosolic sodium concentration increased with spatial heterogeneities, local hotspots with [Na⁺]_c>24 mM appeared close to surface membrane and t-tubules (pseudoratiometric imaging using Sodium Green fluorescence). Electronprobe microanalysis confirmed this result and indicated that stretch increased total sodium [Na] in cell compartments such as mitochondria, nuclear envelope and nucleus. Our results obtained by local stretch differ from those obtained by end-to-end stretch (literature). We speculate that channels may be activated not only by axial but also by shear stress, and, that stretch can activate channels outside the deformed sarcomeres via second messenger.     

Physiological Cost of Physical Exercise and Mitochondrial Volume in Working Muscles of Subjects Exposed to Long-Term Hypokinesia: Effects of Local Resistance Exercise

The results of changes in the physiological cost of 30-min submaximal aerobic bicycle ergometric exercise and characteristics of the mitochondrial apparatus of m. vastus lateralis were assessed comparatively during 120-day (–6°) antiorthostatic hypokinesia either without prophylactic measures or with low-intensity resistance exercise training for 60 days using a Penguin exercise suit. Hypokinesia was accompanied by an increase in the working heart rate and lactate accumulation in the blood during the test exercise, as well as by a decrease in the myofibril size and the volume density of mitochondria in the m. vastus lateralis fibers. The patterns of dynamic changes in the lactate concentration in the blood during exercise training and in the volume density of central mitochondria were found to be similar. A correlation between the rate of lactate accumulation in the blood during the test exercise and the volume density of mitochondria in the working muscle appeared after long-term (60 days) exposure to hypokinesia. The use of the Penguin exercise suit in dynamic mode during prolonged (60-day) exposure to hypokinesia completely prevented the following effects: atrophy of slow-type fibers, a decrease in the volume density of central mitochondria, and an increase in the level of lactate accumulation in the blood under conditions of a standard submaximal aerobic exercise load. The correlation links between the oxidative potential of working muscle and the energy supply of muscular work are discussed.