Dynamic nuclear structure emerges from chromatin crosslinks and motors

The cell nucleus houses the chromosomes, which are linked to a soft shell of lamin filaments. Experiments indicate that correlated chromosome dynamics and nuclear shape fluctuations arise from motor activity. To identify the physical mechanisms, we develop a model of an active, crosslinked Rouse chain bound to a polymeric shell. System-sized correlated motions occur but require both motor activity {\it and} crosslinks. Contractile motors, in particular, enhance chromosome dynamics by driving anomalous density fluctuations. Nuclear shape fluctuations depend on motor strength, crosslinking, and chromosome-lamina binding. Therefore, complex chromatin dynamics and nuclear shape emerge from a minimal, active chromosome-lamina system.Comment: 18 pages, 21 figure

Self-Reported Pain in Male and Female Iraq/Afghanistan-Era Veterans: Associations with Psychiatric Symptoms and Functioning

Objective. To examine pain symptoms and co-occurring psychiatric and functional indices in male and female Iraq/Afghanistan-era veterans. Design. Self-reported data collection and interviews of Iraq/Afghanistan-era veterans who participated in a multisite study of postdeployment mental health. Setting. Veterans were enrolled at one of four participating VA sites. Subjects. Two thousand five hundred eighty-seven male and 662 female Iraq/Afghanistan-era veterans. Methods. Nonparametric Wilcoxon rank tests examined differences in pain scores between male and female veterans. Chi-square tests assessed differences between male and female veterans in the proportion of respondents endorsing moderate to high levels of pain vs no pain. Multilevel regression analyses evaluated the effect of pain on a variety of psychiatric and functional measures. Results. Compared with males, female veterans reported significantly higher mean levels of headache (P \u3c 0.0001), muscle soreness (P \u3c 0.008), and total pain (P \u3c 0.0001), and were more likely to report the highest levels of headache (P \u3c 0.0001) and muscle soreness (P \u3c 0.0039). The presence of pain symptoms in Iraq/Afghanistan-era veterans was positively associated with psychiatric comorbidity and negatively associated with psychosocial functioning. There were no observed gender differences in psychiatric and functional indices when levels of pain were equated. Conclusions. Although female Iraq/Afghanistan-era veterans reported higher levels of pain than male veterans overall, male and female veterans experienced similar levels of psychiatric and functional problems at equivalent levels of reported pain. These findings suggest that pain-associated psychological and functional impacts are comparable and consequential for both male and female veterans

Modulators of Cytoskeletal Reorganization in CA1 Hippocampal Neurons Show Increased Expression in Patients at Mid-Stage Alzheimer's Disease

During the progression of Alzheimer's disease (AD), hippocampal neurons undergo cytoskeletal reorganization, resulting in degenerative as well as regenerative changes. As neurofibrillary tangles form and dystrophic neurites appear, sprouting neuronal processes with growth cones emerge. Actin and tubulin are indispensable for normal neurite development and regenerative responses to injury and neurodegenerative stimuli. We have previously shown that actin capping protein beta2 subunit, Capzb2, binds tubulin and, in the presence of tau, affects microtubule polymerization necessary for neurite outgrowth and normal growth cone morphology. Accordingly, Capzb2 silencing in hippocampal neurons resulted in short, dystrophic neurites, seen in neurodegenerative diseases including AD. Here we demonstrate the statistically significant increase in the Capzb2 expression in the postmortem hippocampi in persons at mid-stage, Braak and Braak stage (BB) III-IV, non-familial AD in comparison to controls. The dynamics of Capzb2 expression in progressive AD stages cannot be attributed to reactive astrocytosis. Moreover, the increased expression of Capzb2 mRNA in CA1 pyramidal neurons in AD BB III-IV is accompanied by an increased mRNA expression of brain derived neurotrophic factor (BDNF) receptor tyrosine kinase B (TrkB), mediator of synaptic plasticity in hippocampal neurons. Thus, the up-regulation of Capzb2 and TrkB may reflect cytoskeletal reorganization and/or regenerative response occurring in hippocampal CA1 neurons at a specific stage of AD progression

Filament Depolymerization Can Explain Chromosome Pulling during Bacterial Mitosis

Chromosome segregation is fundamental to all cells, but the force-generating mechanisms underlying chromosome translocation in bacteria remain mysterious. Caulobacter crescentus utilizes a depolymerization-driven process in which a ParA protein structure elongates from the new cell pole, binds to a ParB-decorated chromosome, and then retracts via disassembly, pulling the chromosome across the cell. This poses the question of how a depolymerizing structure can robustly pull the chromosome that disassembles it. We perform Brownian dynamics simulations with a simple, physically consistent model of the ParABS system. The simulations suggest that the mechanism of translocation is “self-diffusiophoretic”: by disassembling ParA, ParB generates a ParA concentration gradient so that the ParA concentration is higher in front of the chromosome than behind it. Since the chromosome is attracted to ParA via ParB, it moves up the ParA gradient and across the cell. We find that translocation is most robust when ParB binds side-on to ParA filaments. In this case, robust translocation occurs over a wide parameter range and is controlled by a single dimensionless quantity: the product of the rate of ParA disassembly and a characteristic relaxation time of the chromosome. This time scale measures the time it takes for the chromosome to recover its average shape after it is has been pulled. Our results suggest explanations for observed phenomena such as segregation failure, filament-length-dependent translocation velocity, and chromosomal compaction