Interphase chromosomes undergo constrained diffusional motion in living cells

Background: Structural studies of fixed cells have revealed that interphase chromosomes are highly organized into specific arrangements in the nucleus, and have led to a picture of the nucleus as a static structure with immobile chromosomes held in fixed positions, an impression apparently confirmed by recent photobleaching studies. Functional studies of chromosome behavior, however, suggest that many essential processes, such as recombination, require interphase chromosomes to move around within the nucleus.Results: To reconcile these contradictory views, we exploited methods for tagging specific chromosome sites in living cells of Saccharomyces cerevisiae with green fluorescent protein and in Drosophila melanogaster with fluorescently labeled topoisomerase ll. Combining these techniques with submicrometer single-particle tracking, we directly measured the motion of interphase chromatin, at high resolution and in three dimensions. We found that chromatin does indeed undergo significant diffusive motion within the nucleus, but this motion is constrained such that a given chromatin segment is free to move within only a limited subregion of the nucleus. Chromatin diffusion was found to be insensitive to metabolic inhibitors, suggesting that it results from classical Brownian motion rather than from active motility. Nocodazole greatly reduced chromatin confinement, suggesting a role for the cytoskeleton in the maintenance of nuclear architecture.Conclusions: We conclude that chromatin is free to undergo substantial Brownian motion, but that a given chromatin segment is confined to a subregion of the nucleus. This constrained diffusion is consistent with a highly defined nuclear architecture, but also allows enough motion for processes requiring chromosome motility to take place. These results lead to a model for the regulation of chromosome interactions by nuclear architecture.     

From mitochondrial dynamics to arrhythmias

The reactive oxygen species (ROS)-dependent mitochondrial oscillator described in cardiac cells exhibits at least two modes of function under physiological conditions or in response to metabolic and oxidative stress. Both modes depend upon network behavior of mitochondria. Under physiological conditions cardiac mitochondria behave as a network of coupled oscillators with a broad range of frequencies. ROS weakly couples mitochondria under normal conditions but becomes a strong coupling messenger when, under oxidative stress, the mitochondrial network attains criticality. Mitochondrial criticality is achieved when a threshold of ROS is overcome and a certain density of mitochondria forms a cluster that spans the whole cell. Under these conditions, the slightest perturbation triggers a cell-wide collapse of the mitochondrial membrane potential, Δψ_m, visualized as a depolarization wave throughout the cell which is followed by whole cell synchronized oscillations in Δψ_m, NADH, ROS, and GSH. This dynamic behavior scales from the mitochondrion to the cell by driving cellular excitability and the whole heart into catastrophic arrhythmias. A network collapse of Δψ_m under criticality leads to: (i) energetic failure, (ii) temporal and regional alterations in action potential (AP), (iii) development of zones of impaired conduction in the myocardium, and, ultimately, (iv) a fatal ventricular arrhythmia.     

Time course of hemorheological alterations after heavy anaerobic exercise in untrained human subjects.

The time course of hemorheological alterations was investigated after heavy anaerobic exercise in untrained male human subjects. The Wingate protocol was performed by each subject, and blood lactate, red blood cell (RBC) deformability and aggregation, white blood cell (WBC) activation, and several hematological parameters were investigated during 24 h after the exercise and compared with preexercise values. Compared with the preexercise value, blood lactate level was found to be approximately 10-fold higher immediately after the exercise. There was a transient, significant increment of RBC and WBC counts immediately after exercise that was followed by a decrement of RBC count. There was a second increase of WBC count, accompanied with increased percentages of granulocytes and granulocyte activation, starting 45 min after exercise. RBC deformability was found to be impaired immediately after exercise and remained reduced for at least 12 h; RBC aggregation was also found to be decreased after exercise, with the onset of this decrease delayed by 30 min. The results of this study indicate that a single bout of heavy anaerobic exercise may induce significant hemorheological deterioration lasting for up to 12 h and thus suggest the need to consider such effects in individuals with impaired cardiovascular function.     

Anthraquinones in Digitalis species

Twenty anthraquinones have been found in the roots of Digitalis trojana of which the following are new: digitopurpone-1-methyl ether, ω-hydroxypacybasin and ω-hydroxyziganein. The biogenesis of the thirty anthraquinones now known in Digitalis s.l. is discussed.     

Wilson disease mutations associated with uncommon haplotypes in mediterranean patients

This study reports 12 novel mutations of the Wilson disease (WD) gene which have been detected by the molecular analysis of 29 patients of Mediterranean descent carrying uncommon chromosomal haplotypes at the WD locus. These mutations include two nonsense, one splice site and nine missense. The missense mutations lie in regions of the WD gene critical for its function, such as the transmembrane region, the transduction domain and the ATP loop and ATP-binding domain, indicating that they are disease-causing mutations. These new findings improve our knowledge for the role played by functional domains on the ATP7B function. Received: 20 March 1996