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Biomedical subjects

J V Shah

Publications and source records attributed to J V Shah.

At least 19 recordsLinked to original sources
PubMed2004

Controlled ablation of microtubules using a picosecond laser.

The use of focused high-intensity light sources for ablative perturbation has been an important technique for cell biological and developmental studies. In targeting subcellular structures many studies have to deal with the inability to target, with certainty, an organelle or large macromolecular complex. Here we demonstrate the ability to selectively target microtubule-based structures with a laser microbeam through the use of enhanced yellow fluorescent protein (EYFP) and enhanced cyan fluorescent protein (ECFP) variants of green fluorescent protein fusions of tubule. Potorous tridactylus (PTK2) cell lines were generated that stably express EYFP and ECFP tagged to the alpha-subunit of tubulin. Using microtubule fluorescence as a guide, cells were irradiated with picosecond laser pulses at discrete microtubule sites in the cytoplasm and the mitotic spindle. Correlative thin-section transmission electron micrographs of cells fixed one second after irradiation demonstrated that the nature of the ultrastructural damage appeared to be different between the EYFP and the ECFP constructs suggesting different photon interaction mechanisms. We conclude that focal disruption of single cytoplasmic and spindle microtubules can be precisely controlled by combining laser microbeam irradiation with different fluorescent fusion constructs. The possible photon interaction mechanisms are discussed in detail.

Bacterial Proteins↗
PubMed2001

Counterion-induced actin ring formation.

Actin filaments form rings and loops when > 20 mM divalent cations are added to very dilute solutions of phalloidin-stabilized filamentous actin (F-actin). Some rings consist of very long single actin filaments partially overlapping at their ends, and others are formed by small numbers of filaments associated laterally. In some cases, undulations of the rings are observed with amplitudes and dynamics similar to those of the thermal motions of single actin filaments. Lariat-shaped aggregates also co-exist with rings and rodlike bundles. These polyvalent cation-induced actin rings are analogous to the toroids of DNA formed by addition of polyvalent cations, but the much larger diameter of actin rings reflects the greater bending stiffness of F-actin. Actin rings can also be formed by addition of streptavidin to crosslink sparsely biotinylated F-actin at very low concentrations. The energy of bending in a ring, calculated from the persistence length of F-actin and the ring diameter, provides an estimate for the adhesion energy mediated by the multivalent counterions, or due to the streptavidin-biotin bonds, required to keep the ring closed.

Actins↗
PubMed2000

Bidirectional translocation of neurofilaments along microtubules mediated in part by dynein/dynactin.

Neuronal cytoskeletal elements such as neurofilaments, F-actin, and microtubules are actively translocated by an as yet unidentified mechanism. This report describes a novel interaction between neurofilaments and microtubule motor proteins that mediates the translocation of neurofilaments along microtubules in vitro. Native neurofilaments purified from spinal cord are transported along microtubules at rates of 100-1000 nm/s to both plus and minus ends. This motion requires ATP and is partially inhibited by vanadate, consistent with the activity of neurofilament-bound molecular motors. Motility is in part mediated by the dynein/dynactin motor complex and several kinesin-like proteins. This reconstituted motile system suggests how slow net movement of cytoskeletal polymers may be achieved by alternating activities of fast microtubule motors.

Animals↗
PubMed1999

Brains and brawn: plectin as regulator and reinforcer of the cytoskeleton.

Plectin is a 580 kDa intracellular protein, previously shown to link intermediate filaments with microtubules, actin filaments, and membrane components. Disruption of the plectin gene in humans and in mice results in severe skin blistering and muscular degeneration, consistent with plectin's structural role in stabilizing cells against mechanical force. However, recent work by Andra et al. characterizing cells from plectin-deficient mice demonstrates that in addition to this structural role, plectin also modulates the dynamics of the actin cytoskeleton. This makes plectin unusual in that it serves both to reinforce and crosslink intermediate filament attachments to membranes and other cytoskeletal polymers and to regulate actin dynamics in cells.

Actins↗
PubMed1998

Hebbian learning in parallel and modular memories.

Many cognitive and sensorimotor functions in the brain involve parallel and modular memory subsystems that are adapted by activity-dependent Hebbian synaptic plasticity. This is in contrast to the multilayer perceptron model of supervised learning where sensory information is presumed to be integrated by a common pool of hidden units through backpropagation learning. Here we show that Hebbian learning in parallel and modular memories is more advantageous than backpropagation learning in lumped memories in two respects: it is computationally much more efficient and structurally much simpler to implement with biological neurons. Accordingly, we propose a more biologically relevant neural network model, called a tree-like perceptron, which is a simple modification of the multilayer perceptron model to account for the general neural architecture, neuronal specificity, and synaptic learning rule in the brain. The model features a parallel and modular architecture in which adaptation of the input-to-hidden connection follows either a Hebbian or anti-Hebbian rule depending on whether the hidden units are excitatory or inhibitory, respectively. The proposed parallel and modular architecture and implicit interplay between the types of synaptic plasticity and neuronal specificity are exhibited by some neocortical and cerebellar systems.

Cerebellum↗
PubMed1984

Peripheral location of the Y chromosome: relationship to race and length heteromorphism.

In the present report we examined the position of the Y chromosome with respect to its size and race to determine their relationship to its peripheral location. Peripheral blood lymphocytes were cultured from 172 normal male individuals (70 Asian Indians; 49 American Blacks; and 53 Caucasians) and 2770 QFQ cells were photographed. The length of the Y chromosome was classified into four groups i.e., small, average, large and very large as described earlier (Verma et al., J. Med. Genet., 15, 227-281, 1978). The average incidence of peripheral location of all races for small, average, large and very large was 3.64, 5.84, 10.51 and 11.17 per cent respectively. For blacks and caucasians, the peripheral location was influenced by its size while the incidence remained the same for Indians for all sizes. Consequently, it is presumed that the position of the Y chromosome in somatic metaphases depends upon race as well as its size. Furthermore, we have provided a method for determining the position of the Y chromosome which should suffice for most situations.

Asian People↗
PubMed1984

Expression of ribosomal cistrons of human chromosomes at high resolution.

The expression of ribosomal cistrons in the nucleolar organizer regions (NORs) has been studied with high resolution banding in the acrocentric chromosomes of 10 normal individuals. It was found that if a particular chromosome did not stain with silver nitrate at metaphase, then it did not stain at prophase either. Therefore, it is concluded that some of the acrocentric chromosomes have variable expression of NORs.

Adult↗
PubMed1983

Preferential association of nucleolar organizing human chromosomes as revealed by silver staining technique at mitosis.

The frequency of different types of satellite associations of nucleolar organizing human chromosomes (i.e. acrocentric chromosomes; 13, 14, 15, 21, and 22) is reported using 10 normal individuals by Ag-staining technique. The preferential involvement of acrocentric chromosomes in satellite association is suggested. Only acrocentric chromosomes with active NORs (i.e. Ag-stained) were found in association while unstained (inactive NORs) chromosomes were never seen in satellite association. In general as number of NORs expression increase, the frequency of association per cell was also increased. A possible mechanism and the clinical consequences of such an unusual phenophenon is described.

Chromosomes, Human, 13-15↗
PubMed1983

Size of Y chromosome not associated with abortion risk.

The average length of the Y chromosome in men whose wives had multiple fetal loss was 1.046 +/- 0.106, which is not significantly different from the average length in controls (1.068 +/- 0.096). Therefore, it is concluded that there is no evidence for an association of the size of the Y chromosome with an increased risk of abortions as previously suggested. Furthermore, the authors suggest that the definition of a large Y be revised, as the majority of normal males have a Y/F index of more than 1.0, so a Y/F ratio of greater than 1.0 should not be considered a long Y chromosome.

Abortion, Habitual↗