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Biomedical subjects

S Dasgupta

Publications and source records attributed to S Dasgupta.

At least 55 records · Page 3Linked to original sources
PubMed2000

Plasmid R1 is present as clusters in the cells of Escherichia coli.

Fluorescence microscopy was used to determine the location(s) of the replication origin of plasmid R1 in exponentially growing cells of Escherichia coli. The number of oriR1 foci per cell was smaller than the number of R1 copies per cell and was found to be the same for a copA mutant of R1 and for the wild-type plasmid. The intensities of individual foci were stronger for the cop mutant than for the wild type. We interpreted these results to imply that the plasmid DNA molecules were localized in small groups/clusters, a result that seems contrary to the earlier observations that plasmid R1 replicates randomly and segregates as a single-copy unit. The implications for the quantitative behavior of plasmid R1 in stability, incompatibility tests, replication, and partition experiments are discussed.

Escherichia coli↗
PubMed2000

Role of the mukB gene in chromosome and plasmid partition in Escherichia coli.

The intracellular locations of oriC and oriR1, the replication origins of the chromosome and plasmid R1, respectively, were visualized by fluorescence in situ hybridization (FISH) in exponentially growing populations of Escherichia coli. The locations of oriC and oriR1 (from a Par+ R1 plasmid) were unique and different in the wild-type host. In a mukB mutant, the positions were perturbed for both origins. The position of oriR1 from a plasmid with active partition (Par+) in the mukB host was as randomized as that of oriR1 from the Par- plasmid in a wild-type host. However, this mukB-induced randomization did not result in unstable inheritance of the Par+ plasmid, as measured by the conventional segregation assay. This might result from the preferential association of the Par+ plasmid with the bigger, decondensed nucleoid-containing daughters during cell division of MukB- cells, whereas the Par- plasmids were distributed at random and were lost by frequently ending up in anucleate cells.

Bacterial Proteins↗
PubMed2000

Effect of cationic amino acid, L-lysine and its polymers on the growth and secretion of hybridoma cell line OKT-3.

Apart from their pivotal roles in anabolic protein synthesis, cationic amino acids, particularly, L-lysine HCl and its oligomers, up to molecular weight 1000, showed a remarkable property of cellular growth stimulation both in vitro and in vivo. L- and D-Lysine HCl, at a maximal stimulatory concentration of 7 microg/mL of added load of the amino acid, supported a characteristic time-scaled cellular expansion in vitro, and L-lysine-mediated cell expansion in batch cultures always showed a stimulation index (S.I.) ranging up to approximately 35, compared with the matched control populations. Variable S.I. was possibly due to factors such as seeding density, type of media additives, number of passages the cells have undergone before being stimulated, etc. Beyond and before maximal stimulatory concentration of the amino acid, there is a sharp decline in the cellular growth-promoting activity of monomeric L-lysine HCl in vitro, thereby showing a clear concentration window for maximum cellular growth promotion. While the essential amino acid does not have any dedicated cell surface receptor, the monomeric and oligomeric amino acid molecule(s) possibly mediates the serum-derived growth factor-receptor binding on the cell membrane by having two cationic charge centres at two ends of the molecule. Beyond a cutoff molecular weight of 1000, oligomeric lysines did not show any positive effects on either cell division and secretion.

Animals↗
PubMed2000

New genes with old modus operandi. The connection between supercoiling and partitioning of DNA in Escherichia coli.

The process of partitioning bacterial sister chromosomes into daughter cells seems to be distinct from chromatid segregation during eukaryotic mitosis. In Escherichia coli, partitioning starts soon after initiation of replication, when the two newly replicated oriCs move from the cell centre to quarter positions within the cell. As replication proceeds, domains of the compact, supercoiled chromosome are locally decondensed ahead of the replication fork. The nascent daughter chromosomes are recondensed and moved apart through the concerted activities of topoisomerases and the SeqA (sequestration) and MukB (chromosome condensation) proteins, all of which modulate nucleoid superhelicity. Thus, genes involved in chromosome topology, once set aside as 'red herrings' in the search for 'true' partition functions, are again recognized as being important for chromosome partitioning in E. coli.

Bacterial Outer Membrane Proteins↗
PubMed2000

Escherichia coli cell cycle control genes affect chromosome superhelicity.

We have used ethidium bromide titration for direct measurement of the changes in the negative supercoiling of Escherichia coli chromosome caused by mutations inactivating the cell cycle functions mukB and seqA. The amounts of the intercalative agent required to relax the supercoiled chromosome in mukB and seqA mutants were lower and higher, respectively, than for the wild-type parent, confirming that these cell cycle genes modulate the topology of the E. coli chromosome. Plasmid superhelicity measured in these mutant strains showed similar effects albeit of reduced magnitude. As the effects of mukB and seqA mutations were not restricted to the chromosome alone, MukB and SeqA proteins possibly interact with factors involved in the maintenance of intracellular DNA topology. To our knowledge, this is the first direct demonstration of the influence of mukB and seqA genes on the superhelicity of the E. coli chromosome.

Bacterial Outer Membrane Proteins↗
PubMed2000

Molecular characterization and immunohistochemical localization of IV(4)GalNAcGgOse(4)Cer: a naturally occurring novel neutral glycosphingolipid in bovine brain.

A pair of novel neutral glycosphingolipids (Ngsls) has been identified in bovine brain. Their mobilities on thin layer chromatography were slightly different from a standard pentaglycosylceramide (nLcOse(5)Cer from bovine erythrocytes). The compounds were purified to homogeneity by column chromatography. Their fatty acid and base compositions, their monosaccharide compositions and sugar linkage positions were determined by gas-liquid chromato-graphy/mass spectrometry. Carbohydrate sequence analy-sis by(1)H NMR spectroscopy and stepwise exoglyco-sidase digestion indicated the following pentaglycosyl structure for the oligosaccharide moiety of both Ngsls: GalNAcbeta1-4Galbeta1-3GalNAcbeta1-4Galbeta1-4Gl c. The two Ngsls (abbreviated as IV(4)GalNAcGgOse(4)Cer or GalNAc-GA1), differ in their ceramide compositions, having d18:0 and d18:1 sphingosine as their long chain bases. A monospecific polyclonal anti-GalNAc-GA1 antibody, prepared in rabbit and purified by affinity chromatography, stained the neurons of cerebral cortex and cerebellum including Purkinje cells in adult rat brain, indicating that the novel GalNAc-GA1 is associated with cerebellar and other neurons in vertebrate central nervous system.

Animals↗
PubMed2000

Quantum hopping models for kinetic processes

We propose that a quantum operator, apart from representing quantum dynamics, may also represent a dynamical (steady-state) situation of a classical system. We consider a Hamiltonian that describes hopping of single (spinless, noninteracting) bosons to nearest-neighbor sites in a hypercubic lattice and find exactly the mass distribution (in arbitrary dimension) for the ground state and the first excited state. The density shows a peak at a mass equal to the density. A variant of this Hamiltonian is shown to have an exponential mass distribution (in the ground state) that is identical with an analogous classical model.

Journal Article↗
PubMed2000

Effect of nickel on testicular nucleic acid concentrations of rats on protein restriction.

The nucleic acids (DNA and RNA) and total protein concentration in testes were estimated in male Wistar strain rats treated intraperitorally with nickel sulfate (2.0 mg/100 g body weight) on alternate days for 10 dosages. In both normal (18% casein) and protein-restricted (5% casein) experimental animals, the nucleic acids and total protein concentration were found to decrease significantly compared to the corresponding controls. Sperm count and sperm motility were also reduced in both experimental groups of animals. The results indicate that nickel influences the expression of genetic information by reducing testicular nucleic acids and protein concentration in both dietary experimental groups.

Animals↗
PubMed2000

Immunology of cancer cervix.

It is not clear how much genetic factor is responsible for causing cervical cancer, but certainly there has some mutation abnormality in the suppressive p53 gene which is to be proved beyond doubt. In addition to this, there are some environmental factors which make insults on cervical epithelium. Immunology of cancer cervix is well represented by (1) immunology of cancer, (2) immunology of virally controlled antigen and (3) cancer cervix antigen markers. The cancer is an example of transplantation immunology changes in the surface of tumour cells during replication. Human papillomavirus (HPV) DNA has been shown to be associated with high grade cervical intra-epithelial neoplasia (CIN). Squamous cell carcinoma antigen has been investigated for predictive value in cancer cervix. Colony stimulating factor-1 causes monocytic cells aggregation in neoplastic area and plays as initiators of the sequence of inflammation up to neoplasia.

Antigens, Viral↗
PubMed2000

The origins and nature of the cognitive paradigm: an overview.

Although cognitive science, the 'science of mind' is generally regarded as of relatively recent vintage, its origins can actually be traced back to ideas from the 1930s. The purpose of this paper is to offer a view of the essential nature of what has come to be called the cognitive paradigm--the framework around which cognitive science has come to be constructed--and about its origins and development. Of particular note is the interdisciplinarity of the field, with its strong links to psychology, linguistics, neurobiology, computer science and philosophy. As will be explained below, this interdisciplinary character is rooted in the historical development of the science itself, and can only be understood in such a context. Thus, the present article is strongly historical in spirit and content.

Artificial Intelligence↗
PubMed1999

Immunosuppression in hamsters with progressive visceral leishmaniasis: an evaluation of the role of nitric oxide toward impairment of the lymphoproliferative response.

The progressive visceral infection caused in golden hamsters by Leishmania donovani amastigotes led to gradual impairment of the proliferative response of their splenic (SPMC) or peripheral blood (PBMC) mononuclear cells to in vitro stimulation with leishmanial antigen, with mitogen (concanavalin A), and even with a combination of phorbol myristate acetate (PMA) and ionomycin (Io). Removal of macrophage-like adherent cells from SPMC or PBMC of infected animals, however, almost completely restored their proliferative response to PMA + Io, thus ruling out the possibility of any intrinsic defect in the signal-transduction pathways of lymphocyte activation and proliferation. Subsequent studies demonstrated that the generation of soluble mediators such as nitric oxide by these adherent cells is responsible, albeit partially, for the down-regulation of the lymphoproliferative response in hamsters with visceral leishmaniasis.

Animals↗
PubMed1999

Therapeutic and prophylactic uses of protein A in the control of Leishmania donovani infection in experimental animals.

The role of the immunomodulator Protein A (PA) (from Staphylococcus aureus, Cowan I strain) in the control of leishmanial infection was studied in experimental animals. Treatment of Leishmania donovani infected hamsters with PA led to a moderate level of reduction of parasite load in their spleen (68%) and liver (46%). However, combination therapy of PA with the antileishmanial drug stibanate induced a more marked reduction of the spleen (88%) and liver (85%) parasitemia compared to that induced by PA or drug treatment alone. Similar results were also obtained with L. donovani infected BALB/c mice as the combination therapy of PA and stibanate led to a significant reduction (84%) of liver parasite load in comparison to that induced by PA (38%) or drug (61%) treatment alone. Apart from its therapeutic use, PA could also be used as a prophylactic agent in the control of leishmanial infection. Thus, treatment of hamsters with PA before leishmanial challenge significantly reduced their organ parasite load (by 59-78%) compared to that observed in infected controls without prior PA treatment. The antileishmanial effect of PA was likely to be mediated through the activation of macrophages leading to an enhancement of their phagocytic as well as leishmaniacidal activities. Subsequent studies demonstrated that PA treatment led to an increased production of nitric oxide by macrophages which could primarily be responsible for their enhanced parasite killing ability.

Adjuvants, Immunologic↗
PubMed1999

Mutual suppression of mukB and seqA phenotypes might arise from their opposing influences on the Escherichia coli nucleoid structure.

A strain of Escherichia coli in which both the seqA and mukB genes were inactivated displayed partial suppressions of their individual phenotypes. Temperature sensitivity, anucleate cell production and poor nucleoid folding seen in the mukB strain were suppressed by the seqA null mutation, whereas filamentation, asymmetric septation and compact folding of the nucleoids observed in the seqA strain were suppressed by inactivation of the mukB gene function. However, the asynchronous initiation of chromosome replication in the seqA strain was not reversed in the mukBseqA double mutant. Membrane-associated nucleoids were isolated from the wild-type, mukB, seqA and mukBseqA strains and their sedimentation rates were compared under identical conditions. Whereas the mukB mutation caused unfolding of the nucleoid, the seqA mutation led to a more compact packaging of the chromosome. The mukBseqA double mutant regained the wild-type nucleoid organization as revealed from its rate of sedimentation. Microscopic appearances of the nucleoids were consistent with the sedimentation profiles. The mukB mutant was oversensitive to novobiocin and this susceptibility was suppressed in the mukBseqA strain, suggesting possible roles of MukB and SeqA in maintaining chromosome topology. The mutual phenotypic suppression of mukB and seqA alleles thus suggests that these genes have opposing influences on the organization of the bacterial nucleoid.

Bacterial Outer Membrane Proteins↗
PubMed1999

Gentamicin induced inhibition of steroidogenic enzymes in rat testis.

Gentamicin is an aminoglycoside antibiotic, widely used for treating many gram negative bacterial infections. Though nephrotoxicity is the most highlighted side effect, it has also been found to cause an alteration in the phosphatase activities of testes and accessory sex organs and a decline in the sperm count. This study was designed to assess the effects of gentamicin on testicular steroidogenesis and to ascertain whether such alterations are reversible. Laboratory inbred adult, male, 'Wistar' strain rats were chosen as the experimental animal. A significant dose-dependant reduction in the activities of the two steroidogenic enzymes, accompanied with a significant decrease in ascorbic acid and elevation of level of cholesterol was observed. The effects were maximum at a dose of 100 mg/kg, b.wt. After 15 days of withdrawal of the drug therapy the biochemical parameters namely ascorbic acid and cholesterol returned to normal levels whereas the activities of the two dehydrogenases showed a compensatory increase. This indicates that gentamicin affects the steroidogenic enzymes, causing an alteration in the formation of testosterone, which was manifested in the elevated cholesterol in the adult rat testes. However, these alterations were reversible.

17-Hydroxysteroid Dehydrogenases↗
PubMed1999

Pulse polio immunisation, 1995-96: an evaluation in West Bengal.

An evaluation of the Pulse Polio Immunisation Programme (PPI), 1995-96 in West Bengal was undertaken. It was observed that the PPI coverage (with two rounds) was 84.1%. Variations in the PPI coverage level were documented in relation to age, sex, residential status and parental literacy status of the beneficiaries. However, significantly lower PPI coverage was observed among Muslims (p < 0.001) and Scheduled Tribes (p < 0.01). The principal agency responsible for disseminating information about PPI was identified to be the multipurpose health workers. Some of the major reasons for non-acceptance of PPI were lack of information, illness of the child, absence of the child on the "PPI day", lack of faith in immunisation and fear of adverse reaction.

Adolescent↗
PubMed1998

Cell cycle arrest in Era GTPase mutants: a potential growth rate-regulated checkpoint in Escherichia coli.

Era is a low-molecular-weight GTPase essential for Escherichia coli viability. The gene encoding Era is found in the rnc operon, and the synthesis of both RNase III and Era increases with growth rate. Mutants that are partially defective in Era GTPase activity or that are reduced in the synthesis of wild-type Era become arrested in the cell cycle at the predivisional two-cell stage. The partially defective Era GTPase mutation (era1) suppresses several temperature-sensitive lethal alleles that affect chromosome replication and chromosome partitioning but not cell division. Our results suggest that Era plays an important role in cell cycle progression at a specific point in the cycle, after chromosome partitioning but before cytokinesis. Possible functions for Era in cell cycle progression and the initiation of cell division are discussed.

Amino Acid Sequence↗