LAP2alpha maintains a mobile and low assembly state of A-type lamins in the nuclear interior.

Lamins form stable filaments at the nuclear periphery in metazoans. Unlike B-type lamins, lamins A and C localize also in the nuclear interior, where they interact with lamin-associated polypeptide 2 alpha (LAP2α). Using antibody labeling, we previously observed a depletion of nucleoplasmic A-type lamins in mouse cells lacking LAP2α.

Chromatin Viscoelasticity Measured by Local Dynamic Analysis.

The nucleus in eukaryotic cells is a crowded environment that consists of genetic code along the DNA, together with a condensed solution of proteins, RNA, and other molecules. It is subjected to highly dynamic processes, including cell division, transcription, and DNA repair. In addition, the genome in the nucleus is subjected to external forces applied by the cytoplasmic skeleton and neighboring cells, as well as to internal nuclear forces.

Crystallization of Small Organic Molecules in a Polymer Matrix: Multistep Mechanism Enables Structural Control.

The widely employed crystallization of organic molecules in solution is not well understood and is difficult to control. Employing polymers as crystallization media may allow enhanced control via temperature-induced regulation of polymer dynamics. Crystallization of a small organic molecule (perylene diimide) is investigated in polymer matrices (polystyrene) that enable the mechanistic study and control over order evolution.

Sleep increases chromosome dynamics to enable reduction of accumulating DNA damage in single neurons.

Sleep is essential to all animals with a nervous system. Nevertheless, the core cellular function of sleep is unknown, and there is no conserved molecular marker to define sleep across phylogeny. Time-lapse imaging of chromosomal markers in single cells of live zebrafish revealed that sleep increases chromosome dynamics in individual neurons but not in two other cell types.

Chromatin dynamics governed by a set of nuclear structural proteins.

During the past three decades, the study of nuclear and chromatin organization has become of great interest. The organization and dynamics of chromatin are directly responsible for many functions including gene regulation, genome replication, and maintenance. In order to better understand the details of these mechanisms, we need to understand the role of specific proteins that take part in these processes.

Free-Standing Nanocrystalline Materials Assembled from Small Molecules.

We demonstrate a solution-based fabrication of centimeter-size free-standing films assembled from organic nanocrystals based on common organic dyes (perylene diimides, PDIs). These nanostructured films exhibit good mechanical stability, and thermal robustness superior to most plastics, retaining the crystalline microstructure and macroscopic shape upon heating up to 250-300 °C. The films show nonlinear optical response and can be used as ultrafiltration membranes.

Genome organization in the nucleus: From dynamic measurements to a functional model.

A biological system is by definition a dynamic environment encompassing kinetic processes that occur at different length scales and time ranges. To explore this type of system, spatial information needs to be acquired at different time scales. This means overcoming significant hurdles, including the need for stable and precise labeling of the required probes and the use of state of the art optical methods.

Exploring chromatin organization mechanisms through its dynamic properties.

The organization of the genome in the nucleus is believed to be crucial for different cellular functions. It is known that chromosomes fold into distinct territories, but little is known about the mechanisms that maintain these territories. To explore these mechanisms, we used various live-cell imaging methods, including single particle tracking to characterize the diffusion properties of different genomic regions in live cells.

Loss of lamin A function increases chromatin dynamics in the nuclear interior.

Chromatin is organized in a highly ordered yet dynamic manner in the cell nucleus, but the principles governing this organization remain unclear. Similarly, it is unknown whether, and how, various proteins regulate chromatin motion and as a result influence nuclear organization. Here by studying the dynamics of different genomic regions in the nucleus of live cells, we show that the genome has highly constrained dynamics.

Improved estimation of anomalous diffusion exponents in single-particle tracking experiments.

The mean square displacement is a central tool in the analysis of single-particle tracking experiments, shedding light on various biophysical phenomena. Frequently, parameters are extracted by performing time averages on single-particle trajectories followed by ensemble averaging. This procedure, however, suffers from two systematic errors when applied to particles that perform anomalous diffusion.

Universal algorithm for identification of fractional Brownian motion. A case of telomere subdiffusion.

We present a systematic statistical analysis of the recently measured individual trajectories of fluorescently labeled telomeres in the nucleus of living human cells. The experiments were performed in the U2OS cancer cell line. We propose an algorithm for identification of the telomere motion.

Ergodicity convergence test suggests telomere motion obeys fractional dynamics.

Anomalous diffusion, observed in many biological processes, is a generalized description of a wide variety of processes, all obeying the same law of mean-square displacement. Identifying the basic mechanisms of these observations is important for deducing the nature of the biophysical systems measured. We implement a previously suggested method for distinguishing between fractional Langevin dynamics, fractional Brownian motion, and continuous time random walk based on the ergodic nature of the data.

The binding of analogs of porphyrins and chlorins with elongated side chains to albumin.

In previous studies, we demonstrated that elongation of side chains of several sensitizers endowed them with higher affinity for artificial and natural membranes and caused their deeper localization in membranes. In the present study, we employed eight hematoporphyrin and protoporphyrin analogs and four groups containing three chlorin analogs each, all synthesized with variable numbers of methylenes in their alkyl carboxylic chains. We show that these tetrapyrroles' affinity for bovine serum albumin (BSA) and their localization in the binding site are also modulated by chain lengths.

The localization and photosensitization of modified chlorin photosensitizers in artificial membranes.

In this work we investigate the localization and photophysical properties of twelve synthetically derived chlorins in artificial membranes, with the goal of designing more effective photosensitizers for photodynamic therapy (PDT). The studied chlorins incorporate substituents of varying lipophilicity at the C(5)-meso-position (H to C(5)H(11)), while the C(13)- and C(17)-positions have carboxylate "anchoring" groups tethered to the tetrapyrrole by alkyl chains (CH(2))(n) (n = 1-3). It was found that as n increases, the chromophoric part of the molecule, and thus the point of generation of singlet oxygen, is located at a deeper position in the bilayer.

The influence of temperature on photodynamic cell killing in vitro with 5-aminolevulinic acid.

Cell survival was investigated after exposing cells in vitro to different temperatures before or after photodynamic therapy with 5-aminolevulinic acid. The photodynamic process was found to be temperature dependent. Cells exposed for 1h to 41 degrees C before light exposure or to 7 degrees C after light exposure showed decreased survival.

On the correlation between hydrophobicity, liposome binding and cellular uptake of porphyrin sensitizers.

A crucial factor in choosing a porphyrin or analogous photosensitizer for photodynamic therapy (PDT) is its ability to incorporate into the cells. For hydrophobic compounds that partition passively into the cytoplasmic membrane, a partition coefficient between an organic solvent and water, P, is one factor that could be used to predict the molecule's ability to diffuse into biomembranes. We synthesized several porphyrins, modified with two, three or four meso-substituents and studied their spectroscopic and photophysical properties.

The effect of pH on the topography of porphyrins in lipid membranes.

The effect of the acidity of the environment on the topography and photophysics of sensitizer molecules in homogeneous solutions, and when embedded in a lipid microenvironment, was studied. Four hematoporphyrin (HP) analogs were studied, which have chemical "spacers" of varying lengths between the chromophoric tetrapyrrole and the carboxylate moiety. These derivatives have essentially the same chemical attributes and reactivity as the parent compound, HP IX, which is used in clinical procedures of photodynamic therapy.

Porphyrin depth in lipid bilayers as determined by iodide and parallax fluorescence quenching methods and its effect on photosensitizing efficiency.

Photosensitization by porphyrins and other tetrapyrrole chromophores is used in biology and medicine to kill cells. This light-triggered generation of singlet oxygen is used to eradicate cancer cells in a process dubbed "photodynamic therapy," or PDT. Most photosensitizers are of amphiphilic character and they partition into cellular lipid membranes.

DNA-specific antiidiotypic antibodies in the sera of patients with autoimmune diseases.

Blood sera of patients with autoimmune diseases scleroderma (Scl), systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA) have been shown to yield a specific immune response to topoisomerase I, the product of expression of a cDNA fragment cloned into lambda gt11 and monoclonal antibodies (MAB) to the enzyme. The 'topoisomerase test' is not absolutely specific for Scl. The stable positive response of autoimmune sera to anti-topoisomerase monoclonal antibodies has a specific character and is associated with the interaction of the Fab fragment of MAB with the IgG fraction of autoimmune serum.

[Interactions of sera from patients with autoimmune diseases with cDNA expressed fragment of topoisomerase I and monoclonal antibodies against enzyme].

The interaction of sera from 34 patients with different autoimmune diseases with the expressed fusion protein cloned in lambda gt11 vector (topoisomerase I--beta galactosidase) and monoclonal antibodies against enzyme was studied. It was demonstrated that 100% of Scl cases possessed positive activity against fusion protein. It was shown that this test is not absolutely specific for Scl, i.