Delayed self-regulation and time-dependent chemical drive leads to novel states in epigenetic landscapes.

The epigenetic pathway of a cell as it differentiates from a stem cell state to a mature lineage-committed one has been historically understood in terms of Waddington's landscape, consisting of hills and valleys. The smooth top and valley-strewn bottom of the hill represent their undifferentiated and differentiated states, respectively. Although mathematical ideas rooted in nonlinear dynamics and bifurcation theory have been used to quantify this picture, the importance of time delays arising from multistep chemical reactions or cellular shape transformations have been ignored so far. We argue that this feature is crucial in understanding cell differentiation and explore the role of time delay in a model of a single-gene regulatory circuit. We show that the interplay of time-dependent drive and delay introduces a new regime where the system shows sustained oscillations between the two admissible steady states. We interpret these results in the light of recent perplexing experiments on inducing the pluripotent state in mouse somatic cells. We also comment on how such an oscillatory state can provide a framework for understanding more general feedback circuits in cell development.

The role of Lamin A in cytoskeleton organization in colorectal cancer cells: a proteomic investigation.

Up-regulated expression of lamin A has been implicated in increased cell invasiveness and mortality in colorectal cancer. Here we use quantitative proteomics to investigate lamin A regulated changes in the cytoskeleton that might underpin increased cell motility. Using siRNA knockdown of lamin A in a model cell line (SW480/lamA) we confirm that the presence of lamin A promotes cell motility. Using an enhanced technique to prepare cytoskeleton fractions in combination with 2D DiGE we were able to accurately and reproducibly detect changes in the representation of protein species within the cytoskeleton as low as 20%. In total 64 protein spots displayed either increased or decreased representation within the cytoskeleton of SW480/lamA cells compared to controls. Of these the identities of 29 spots were determined by mass spectrometry. A majority were multiple forms of three classes of proteins, including components of the actin and IF cytoskeletons, protein chaperones and translation initiation and elongation factors. In particular our data reveal that the representation of tissue transglutaminase 2, which is known to modify elements of the cytoskeleton and is associated with cancer progression, was highly over-represented in the cytoskeleton fraction of SW480/lamA cells. Overall, our data are consistent with changed protein cross-linking and folding that favours the formation of dynamic actin filaments over stress fibres accounting for the altered cell motility properties in SW480/lamA cells.

Measurements of steady flow through a bileaflet mechanical heart valve using stereoscopic PIV.

Computational modeling of bileaflet mechanical heart valve (BiMHV) flow requires experimentally validated datasets and improved knowledge of BiMHV fluid mechanics. In this study, flow was studied downstream of a model BiMHV in an axisymmetric aortic sinus using stereoscopic particle image velocimetry. The inlet flow was steady and the Reynolds number based on the aortic diameter was 7600. Results showed the out-of-plane velocity was of similar magnitude as the transverse velocity. Although additional studies are needed for confirmation, analysis of the out-of-plane velocity showed the possible presence of a four-cell streamwise vortex structure in the mean velocity field. Spatial data for all six Reynolds stress components were obtained. Reynolds normal stress profiles revealed similarities between the central jet and free jets. These findings are important to BiMHV flow modeling, though clinical relevance is limited due to the idealized conditions chosen. To this end, the dataset is publicly available for CFD validation purposes.

Examining the nootropic effects of a special extract of Bacopa monniera on human cognitive functioning: 90 day double-blind placebo-controlled randomized trial.

While Ayurvedic medicine has touted the cognitive enhancing effects of Bacopa monniera for centuries, there is a need for double-blind placebo-controlled investigations. One hundred and seven healthy participants were recruited for this double-blind placebo-controlled independent group design investigation. Sixty-two participants completed the study with 80% treatment compliance. Neuropsychological testing using the Cognitive Drug Research cognitive assessment system was conducted at baseline and after 90 days of treatment with a special extract of Bacopa monniera (2 x 150 mg KeenMind) or placebo. The Bacopa monniera product significantly improved performance on the 'Working Memory' factor, more specifically spatial working memory accuracy. The number of false-positives recorded in the Rapid visual information processing task was also reduced for the Bacopa monniera group following the treatment period. The current study provides support for the two other published studies reporting cognitive enhancing effects in healthy humans after a 90 day administration of the Bacopa monniera extract. Further studies are required to ascertain the effective dosage range, the time required to attain therapeutic levels and the effects over a longer term of administration.

Depression, social support and adherence to highly active antiretroviral therapy in people living with HIV/AIDS.

BACKGROUND: The present study investigated the prevalence of depression in HIV-positive individuals and its association with adherence to highly active antiretroviral therapy (HAART). METHODS: HIV-positive (n = 80) and HIV-negative (n = 20) participants were assessed for depression and adherence via clinical interview and self-reporting. RESULTS: Fourteen percent of the HIV-seropositive group met the criteria for current mood disorder compared with 5% of controls. Similarly, 39% of the HIV-seropositive participants met the criteria for a past major depressive episode compared with 15% of controls. Non-adherence to HAART was reported by 30.5% of those prescribed HAART and was significantly associated with living alone and relationship status. CONCLUSIONS: The present study found compromised psychological health in people living with HIV infection. It is recommended that health professionals continue to screen for depression, relationship status and living situation to ensure adherence to HAART.

A novel role for the nuclear membrane protein emerin in association of the centrosome to the outer nuclear membrane.

The type II inner nuclear membrane protein emerin is a component of the LINC complex that connects the nuclear lamina to the actin cytoskeleton. In emerin-null or -deficient human dermal fibroblasts we find that the centrosome is detached from the nucleus. Moreover, following siRNA knockdown of emerin in wild-type fibroblasts, the centrosome also becomes detached from the nucleus. We show that emerin interacts with tubulin, and that nocadozole-treated wild-type cells phenocopy the detached centrosome characteristic of emerin-null/deficient cells. We also find that a significant fraction of emerin is located at the outer nuclear membrane and peripheral ER, where it interacts directly with the centrosome. Our data provide the first evidence in mammalian cells as to the nature of the linkage of the centrosome, and therefore the tubulin cytoskeleton, with the outer nuclear membrane.

Nucleoplasmic LAP2alpha-lamin A complexes are required to maintain a proliferative state in human fibroblasts.

In human diploid fibroblasts (HDFs), expression of lamina-associated polypeptide 2 alpha (LAP2alpha) upon entry and exit from G(0) is tightly correlated with phosphorylation and subnuclear localization of retinoblastoma protein (Rb). Phosphoisoforms of Rb and LAP2alpha are down-regulated in G(0). Although RbS780 phosphoform and LAP2alpha are up-regulated upon reentry into G(1) and colocalize in the nucleoplasm, RbS795 migrates between nucleoplasmic and speckle compartments. In HDFs, which are null for lamins A/C, LAP2alpha is mislocalized within nuclear aggregates, and this is correlated with cell cycle arrest and accumulation of Rb within speckles. Nuclear retention of nucleoplasmic Rb during G(1) phase but not of speckle-associated Rb depends on lamin A/C. siRNA knock down of LAP2alpha or lamin A/C in HDFs leads to accumulation of Rb in speckles and G(1) arrest, probably because of activation of a cell cycle checkpoint. Our results suggest that LAP2alpha and lamin A/C are involved in controlling Rb localization and phosphorylation, and a lack or mislocalization of either protein leads to cell cycle arrest in HDFs.

Genomic instability in laminopathy-based premature aging.

Premature aging syndromes often result from mutations in nuclear proteins involved in the maintenance of genomic integrity. Lamin A is a major component of the nuclear lamina and nuclear skeleton. Truncation in lamin A causes Hutchinson-Gilford progerial syndrome (HGPS), a severe form of early-onset premature aging. Lack of functional Zmpste24, a metalloproteinase responsible for the maturation of prelamin A, also results in progeroid phenotypes in mice and humans. We found that Zmpste24-deficient mouse embryonic fibroblasts (MEFs) show increased DNA damage and chromosome aberrations and are more sensitive to DNA-damaging agents. Bone marrow cells isolated from Zmpste24-/- mice show increased aneuploidy and the mice are more sensitive to DNA-damaging agents. Recruitment of p53 binding protein 1 (53BP1) and Rad51 to sites of DNA lesion is impaired in Zmpste24-/- MEFs and in HGPS fibroblasts, resulting in delayed checkpoint response and defective DNA repair. Wild-type MEFs ectopically expressing unprocessible prelamin A show similar defects in checkpoint response and DNA repair. Our results indicate that unprocessed prelamin A and truncated lamin A act dominant negatively to perturb DNA damage response and repair, resulting in genomic instability which might contribute to laminopathy-based premature aging.

A-type lamins: guardians of the soma?

The gene LMNA encodes the proteins lamins A and C and is implicated in nine different laminopathies - inherited diseases that are linked to premature ageing. Recent evidence has demonstrated that lamins A and C have essential functions in protecting cells from physical damage, as well as in maintaining the function of transcription factors required for the differentiation of adult stem cells. Thus, the degenerative nature of laminopathies is explained because these lamins are essential for maintenance of somatic tissues in adulthood.

Laminopathies.

Nuclear lamins form a fibrous nucleoskeletal network of intermediate-sized filaments that underlies the inner nuclear membrane. It associates with this membrane through interactions with specific integral nuclear membrane proteins, while within this flattened lamin lattice the nuclear pore complexes are embedded. Next to this peripheral network, the lamins can form intranuclear structures. The lamins are the evolutionary progenitors of the cytoplasmic intermediate filament proteins and have profound influences on nuclear structure and function. These influences require that lamins have dynamic properties and dual identities as structural building blocks on the one hand, and transcription regulators on the other. Which of these identities underlies the laminopathies, a myriad of genetic diseases caused by mutations in lamins or lamin-associated proteins, is a topic of intense debate.

Luminescent nonacoordinate cationic lanthanide complexes as potential cellular imaging and reactive probes.

Nonacoordinate delta- and lambda-Eu and Tb complexes have been tested as imaging and reactive probes in mouse fibroblast (NIH 3T3) cells. The uptake of these complexes by the cells was assessed by fluorescence microscopy. Complex-induced DNA damage was studied by gel electrophoresis and shown to be a function of complex chirality.