Search PubMed⌕ Search

Biomedical subjects

A Saxena

Publications and source records attributed to A Saxena.

At least 19 recordsLinked to original sources
PubMed2006

Analysis of the Leishmania donovani transcriptome reveals an ordered progression of transient and permanent changes in gene expression during differentiation.

Leishmania donovani is an intracellular protozoan parasite that causes kala-azar in humans. During infection the extracellular insect forms (promastigotes) undergo rapid differentiation to intracellular amastigotes that proliferates in phagolysosomes of mammalian macrophages. We used microarray-based expression profiling to investigate the time-course of changes in RNA abundance during promastigote-to-amastigote differentiation in a host-free system that mimics this process. These studies revealed that several hundred genes underwent an ordered progression of transient or permanent up- and down-regulation during differentiation. Genes that were permanently up-regulated in amastigotes were enriched for transporters and surface proteins, but under-represented in genes involved in protein and other metabolism. Most of these changes occurred late in the differentiation process, when morphological differentiation was essentially complete. Down-regulated genes were over-represented in those involved in cell motility, growth and/or maintenance, and these changes generally occurred earlier in the process. Genes that were transiently up- or down-regulated during differentiation included those encoding heat shock proteins, ubiquitin hydrolases, RNA binding proteins, protein kinases, a protein phosphatase, and a histone deacetylase. These results suggest that changes in mRNA abundance may be important in signal transduction, as well as protein and mRNA turnover, during differentiation. In addition to these mRNA changes, other transcripts including one or more rRNAs and snoRNAs, and non-coding RNAs from several telomeres, also showed substantial changes in abundance during the differentiation process. This paper provides the first genome-scale quantitative analysis of gene expression during the transition from promastigotes to amastigotes and demonstrates the utility of the host-free differentiation system.

Animals↗
PubMed2006

Statics and dynamics of an inhomogeneously nonlinear lattice.

We introduce an inhomogeneously nonlinear Schrödinger lattice, featuring a defocusing segment, a focusing segment and a transitional interface between the two. We illustrate that such inhomogeneous settings present vastly different dynamical behavior in the vicinity of the interface than the one expected in their homogeneous counterparts. We analyze the relevant stationary states, as well as their stability, by means of perturbation theory and linear stability analysis. We find good agreement with the numerical findings in the vicinity of the anticontinuum limit. For larger values of the coupling, we follow the relevant branches numerically and show that they terminate at values of the coupling strength which are larger for more extended solutions. The dynamical development of relevant instabilities is also monitored in the case of unstable solutions.

Journal Article↗
PubMed2006

Nucleolin inhibits Hdm2 by multiple pathways leading to p53 stabilization.

Nucleolin is a c-Myc-induced gene product with defined roles in ribosomal RNA processing and the inhibition of chromosomal DNA replication following stress. Here we find that changes in nucleolin protein levels in unstressed cells cause parallel changes in the amount of p53 protein. Alterations in p53 levels arise from nucleolin binding to the p53 antagonist Hdm2, resulting in the inhibition of both p53 ubiquitination and Hdm2 auto-ubiquitination. Nucleolin does not alter p53 ubiquitination by human papillomavirus E6, indicating that the effect is specific for Hdm2. Although the inhibition of ligase activity would be expected to stabilize Hdm2, we instead find that nucleolin also reduces Hdm2 protein levels, demonstrating that nucleolin inhibits Hdm2 using multiple mechanisms. Increases in nucleolin levels in unstressed cells led to higher expression of p21(cip1/waf1), a reduced rate of cellular proliferation, and an increase in apoptosis. Thus, nucleolin has a number of properties in common with the tumor suppressor ARF (alternate reading frame). We propose that nucleolin, like ARF, responds to hyperproliferative signals by upregulation of p53 through Hdm2 inhibition.

Blotting, Western↗
PubMed2006

Pinning frequencies of the collective modes in alpha-uranium.

Uranium is the only known element that features a charge-density wave (CDW) and superconductivity. We report a comparison of the specific heat of single-crystal and polycrystalline alpha-uranium. In the single crystal we find excess contributions to the heat capacity at 41 K, 38 K, and 23 K, with a Debye temperature ThetaD = 265 K. In the polycrystalline sample the heat capacity curve is thermally broadened (ThetaD = 184 K), but no excess heat capacity was observed. The excess heat capacity Cphi (taken as the difference between the single-crystal and polycrystal heat capacities) is well described in terms of collective-mode excitations above their respective pinning frequencies. This attribution is represented by a modified Debye spectrum with two cutoff frequencies, a pinning frequency V0 for the pinned CDW (due to grain boundaries in the polycrystal), and a normal Debye acoustic frequency occurring in the single crystal.

Journal Article↗
PubMed2006

Non-mosaic trisomy 22: a report of 2 cases.

Non-mosaic trisomy 22 is a common cause of first trimester miscarriage and has a livebirth incidence of 1 in 30,000-50,000. Consequently there is a paucity of information for counselling parents. Detection in the second trimester is rare. It is commonly associated with severe growth retardation and multiple structural abnormalities. Oligohydramnios is frequently seen and can make detection of other abnormalities difficult. The outlook is uniformly poor and survival beyond the first trimester may present management dilemmas. A thorough fetal assessment including high-resolution cytogenetics with or without FISH is required for counselling. Careful plans for intrapartum and neonatal management may be necessary. The recurrence risk is thought to be low but information is very limited as there have been no reported cases of recurrence. We present two case of non-mosaic trisomy 22 including the first to be diagnosed subsequent to investigation for a high serum screening Down's risk.

Abnormalities, Multiple↗
PubMed2005

In vitro and in vivo characterization of recombinant human butyrylcholinesterase (Protexia) as a potential nerve agent bioscavenger.

Previous studies in rodents and nonhuman primates have demonstrated that pretreatment with cholinesterases can provide significant protection against behavioral and lethal effects of nerve agent intoxication. Human butyrylcholinesterase (HuBuChE) purified from plasma has been shown to protect against up to 5 x LD50s of nerve agents in guinea pigs and non-human primates, and is currently being explored as a bioscavenger pretreatment for human use. A recombinant form of HuBuChE has been expressed in the milk of transgenic goats as a product called Protexia. Protexia was supplied by Nexia Biotechnologies (Que., Canada) as a purified solution with a specific activity of 600 U/mg. Initial in vitro studies using radiolabeled 3H-soman or 3H-DFP (diisopropyl fluorophosphate) demonstrated that these inhibitors specifically bind to Protexia. When Protexia was mixed with soman, sarin, tabun or VX using varying molar ratios of enzyme to nerve agent (8:1, 4:1, 1:1 and 1:4, respectively), the data indicated that 50% inhibition of enzyme activity occurs around the 1:1 molar ratio for each of the nerve agents. Protexia was further characterized for its interaction with pyridostigmine bromide and six unique carbamate inhibitors of cholinesterase. IC50 and Ki values for Protexia were determined to be very similar to those of HuBuChE purified from human plasma. These data suggest that Protexia has biochemical properties very similar to those HuBuChE when compared in vitro. Together these data the continued development of the goat milk-derived recombinant HuBuChE Protexia as a potential bioscavenger of organophosphorus nerve agents.

Animals↗
PubMed2005

Polyethylene glycosylation prolongs the circulatory stability of recombinant human butyrylcholinesterase.

Previous studies in rodents and non-human primates have demonstrated that pretreatment of animals with cholinesterases could provide significant protection against organophosphate (OP) nerve agent toxicity. Gene delivery/therapy is emerging as an approach to achieve high-level expression of proteins in vivo that are very similar to their native counterparts. Recently, adenoviral (Ad) vectors have proven to be excellent vehicles for delivering genes to cells in vitro and in vivo. In this study, we explored the use of the newly designed AdenoVATOR system for the expression of recombinant human butyrylcholinesterase (rHu BChE) in human embryonic kidney 293A (HEK-293A) cells. In these cells, rHu BChE was expressed as mostly tetrameric form by the simultaneous expression of proline-rich attachment domain. By optimizing the culture conditions, 1.5-2.0 U/ml of rHu BChE could be expressed in HEK-293A cells. Recombinant Hu BChE was purified to homogeneity by ammonium sulfate fractionation followed by affinity column chromatography using procainamide Sepharose and cobalt Sepharose gels. The enzymatic and physico-chemical properties of purified rHu BChE were similar to those of native serum-derived Hu BChE. To determine the suitability of this preparation for use as an antidote against highly toxic nerve agents, its pharmacokinetics were evaluated in mice. Recombinant Hu BChE exhibited a mean residence time of 18.3 h which was 2.5-fold shorter than that observed for native Hu BChE in mice. However, rHu BChE chemically modified with polyethyleneglycol (PEG) displayed a mean residence time of 36.2 h suggesting that PEG-modification can prolong the circulatory stability of rHu BChE. The efficacy of Ad-Hu BChE to induce the production of therapeutic levels of bioscavenger in vivo is under evaluation.

Animals↗
PubMed2005

Lost in translation: translational interference from a recurrent mutation in exon 1 of MECP2.

BACKGROUND: Rett syndrome (RTT) is an X linked neuro-developmental disorder affecting mostly girls. Mutations in the coding region of MECP2 are found in 80% of classic RTT patients. Until recently, the region encoding MECP2 was believed to comprise exons 2, 3, and 4 with the ATG start site located at the end of exon 2 (MeCP2_e2). METHODS: Recent reports of another mRNA transcript transcribed from exon 1 (MeCP2_e1) prompted us to screen exon 1 among RNA samples from 20 females with classic or atypical RTT. RESULTS: A previously reported 11 base pair deletion in exon 1 was detected in one subject with a milder phenotype. Although RNA expression for both protein isoforms was detected from the mutant allele, evaluation of MeCP2 protein in uncultured patient lymphocytes by immunocytochemistry revealed that MeCP2 protein production was restricted to only 74-76% of lymphocytes. X chromosome inactivation studies of genomic DNA revealed similar XCI ratios at the HUMARA locus (73:27 with HpaII and 74:26 with McrBC). We have demonstrated that translation but not transcription of the MeCP2_e2 isoform is ablated by the 11 nucleotide deletion, 103 nucleotides upstream of the e2 translation start site. CONCLUSIONS: These findings reveal that nucleotides within the deleted sequence in the 5'-UTR of the MeCP2_e2 transcript, while not required for transcription, are essential for translation.

Adolescent↗
PubMed2005

Simulations of spinodal nucleation in systems with elastic interactions.

Systems with long-range interactions quenched into a metastable state near the pseudospinodal exhibit nucleation that is qualitatively different from classical nucleation near the coexistence curve. We observe nucleation droplets in Langevin simulations of a two-dimensional model of martensitic transformations and determine that the structure of the nucleating droplet differs from the stable martensite structure. Our results, together with experimental measurements of the phonon dispersion curve, allow us to predict the nature of the droplet. The results have implications for nucleation in many solid-solid transitions and the structure of the final state.

Journal Article↗
PubMed2005

Effects of soman inhibition and of structural differences on cholinesterase molecular dynamics: a neutron scattering study.

Incoherent elastic neutron scattering experiments on members of the cholinesterase family were carried out to investigate how molecular dynamics is affected by covalent inhibitor binding and by differences in primary and quaternary structure. Tetrameric native and soman-inhibited human butyrylcholinesterase (HuBChE) as well as native dimeric Drosophila melanogaster acetylcholinesterase (DmAChE) hydrated protein powders were examined. Atomic mean-square displacements (MSDs) were found to be identical for native HuBChE and for DmAChE in the whole temperature range examined, leading to the conclusion that differences in activity and substrate specificity are not reflected by a global modification of subnanosecond molecular dynamics. MSDs of native and soman-inhibited HuBChE were identical below the thermal denaturation temperature of the native enzyme, indicating a common mean free-energy surface. Denaturation of the native enzyme is reflected by a relative increase of MSDs consistent with entropic stabilization of the unfolded state. The results suggest that the stabilization of HuBChE phosphorylated by soman is due to an increase in free energy of the unfolded state due to a decrease in entropy.

Acetylcholinesterase↗
PubMed2005

Persistent spin currents without spin-orbit coupling in a spin-1/2 ring.

We show that a spatially dependent magnetic field can induce a persistent spin current in a spin-1/2 Heisenberg antiferromagnetic ring, proportional to the solid angle subtended by the magnetic field on a unit sphere. The magnitude of the spin current is determined by the ratio of longitudinal and transverse exchange interactions J(parallel)/J(perpendicular) and by the magnetic field magnitude.

Journal Article↗
PubMed2005

Adaptability and "intermediate phase" in randomly connected networks.

We present a simple model that enables us to analytically characterize a floppy to rigid transition and an associated self-adaptive intermediate phase in a random bond network. In this intermediate phase, the network adapts itself to lower the stress due to constraints. Our simulations verify this picture. We use these insights to identify applications of these ideas in computational problems such as vertex cover and K-satisfiability.

Complex Mixtures↗
PubMed2005

Initial diagnosis of small lymphocytic lymphoma in parotidectomy for Warthin tumour, a rare collision tumour.

Warthin tumours (WT) and malignant lymphomas are only rarely associated, and most are examples of involvement of the lymphoid stroma of WT by a disseminated lymphoma. This report describes a case where excision of a parotid mass led to the initial diagnosis of WT and small lymphocytic lymphoma (SLL). The diagnosis of SLL was confirmed by immunohistochemistry and molecular studies. The patient had stage IV A disease and is currently in chemotherapy induced complete remission. This case highlights the extremely rare association of SLL with WT and the importance of evaluation of the WT stroma, where the pale proliferation centres of SLL may mimic germinal centres of reactive lymphoid nodules.

Adenolymphoma↗
PubMed2004

Solitary wave interactions in dispersive equations using Manton's approach.

We generalize the approach first proposed by Manton [Nucl. Phys. B 150, 397 (1979)] to compute solitary wave interactions in translationally invariant, dispersive equations that support such localized solutions. The approach is illustrated using as examples solitons in the Korteweg-de Vries equation, standing waves in the nonlinear Schrödinger equation, and kinks as well as breathers of the sine-Gordon equation.

Journal Article↗
PubMed2004

Comparison of echo and MRI in the imaging evaluation of intracardiac masses.

We compared the efficacy of echocardiography (ECHO) and magnetic resonance imaging (MRI) for evaluating intracardiac masses. Over an 8-yr period, 28 patients, 21 males, 7 females, 16 days-60 years of age (mean 25 years) with a suspected intracardiac mass on ECHO (transthoracic in all; transesophageal in 9) underwent an MRI examination. Five patients had a contrast-enhanced MRI. ECHO and MRI were compared with respect to their technical adequacy, ability to detect and suggest the likely etiology of the mass, and provide additional information (masses not seen with the other technique, inflow or outflow obstruction, and intramural component of an intracavitary mass). With MRI, the image morphology (including signal intensity changes on the various sequences) and extracardiac manifestations were also evaluated. The diagnosis was confirmed by histopathology in 18, surgical inspection in 4, by follow- up imaging on conservative management in 5, and by typical extracardiac manifestations of the disease in 1 patient. Fifteen (54%) patients had tumors (benign 12, malignant 3), 5 had a thrombus or hematoma, and 4 each had infective or vascular lesions. Thirty-four masses (13 in ventricle, 11 septal, 7 atrial, 2 on valve and 1 in pulmonary artery) were seen on MRI, 28 of which were detected by ECHO. Transthoracic ECHO (TTE) and MRI were technically optimal in 82% and 100% of cases, respectively. Nine patients needed an additional transesophageal ECHO (TEE). Overall, MRI showed a mass in all patients, whereas ECHO missed it in 2 cases. In cases with a mass on both modalities, MRI detected 4 additional masses not seen on ECHO. MRI suggested the etiology in 21 (75%) cases, while the same was possible with ECHO (TTE and TEE) in 8 (29%) cases. Intramural component, extension into the inflow or outflow, outflow tract obstruction, and associated pericardial or extracardiac masses were better depicted on MRI. We conclude that MRI is advantageous over a combination of TTE and TEE for the detection and complete morphological and functional evaluation (hemodynamic effects) of cardiac masses.

Adolescent↗