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B N Singh

Publications and source records attributed to B N Singh.

At least 19 recordsLinked to original sources
PubMed2006

Fluctuating asymmetry in certain morphological traits in laboratory populations of Drosophila ananassae.

Fluctuating asymmetry (FA, subtle random deviations from perfect bilateral symmetry) is often used as a measure of developmental instability (DI), which results from perturbations in developmental pathways caused by genetic or environmental stressors. During the present study, we estimated FA in 5 morphological traits, viz. wing length (WL), wing to thorax ratio (W:T), sternopleural bristle number (SBN), sex-comb tooth number (SCTN), and ovariole number (ON) in 18 laboratory populations of Drosophila ananassae. FA levels of measured traits differed significantly among populations except for SBN (in males and females) and W:T ratio (in females). Positional fluctuating asymmetry (PFA), a sensitive measure of DI, also varied significantly among the populations for SBN in females and SCTN in males. Interestingly, both males and females were similar for nonsexual traits. However, when FA across all traits (sexual and nonsexual) was combined into a single composite index (CFA), significant differences were found for both populations and sexes. Males showed higher CFA values than females, suggesting that males are more prone to developmental perturbations. The magnitude of FA differed significantly among traits, being lowest for nonsexual traits (SBN, WL, W:T ratio) and highest for sexual traits (SCTN and ON). The trait size of sexual traits (SCTN and ON) was positively correlated with their asymmetry. The possible reasons for variation in FA both among traits and among populations, and the usefulness of FA as an indicator of developmental stress and phenotypic quality in D. ananassae are discussed.

Animals↗
PubMed2005

Genetic basis of hybrid male sterility among three closely related species of Drosophila.

The genetic basis of hybrid male sterility among three closely related species, Drosophila bipectinata, D. parabipectinata and D. malerkotliana has been investigated by using backcross analysis methods. The role of Y chromosome, major hybrid sterility (MHS) genes (genetic factors) and cytoplasm (non-genetic factor) have been studied in the hybrids of these three species. In the species pair, bipectinata--parabipectinata, Y chromosome introgression of parabipectinata in the genomic background of bipectinata and the reciprocal Y chromosome introgression were unsuccessful as all males in second backcross generation were sterile. Neither MHS genes nor cytoplasm was found important for sterility. This suggests the involvement of X-Y, X-autosomes or polygenic interactions in hybrid male sterility. In bipectinata--malerkotliana and parabipectinata--malerkotliana species pairs, Y chromosome substitution in reciprocal crosses did not affect male fertility. Backcross analyses also show no involvement of MHS genes or cytoplasm in hybrid male sterility in these two species pairs. Therefore, X- autosome interaction or polygenic interaction is supposed to be involved in hybrid male sterility in these two species pairs. These findings also provide evidence that even in closely related species, genetic interactions underlying hybrid male sterility may vary.

Animals↗
PubMed2005

Genetics of sexual behaviour in Drosophila.

The analysis of genetics of behaviour within and between species provides important clues about the forces shaping the evolution of behavioural genes. In Drosophila, a number of key processes such as emergence from the pupal case, locomotor activity, feeding, olfaction and aspects of mating behaviour are under circadian regulation. Genes controlling sexual behaviour are likely to control species specific differences in courtship that are involved in reproductive isolation of closely related species. Courtship in Drosophila is characterized by a series of stereotyped behaviours that lead to copulation and more than 30 genes have been identified through mutations that affect one or more of these elements. Although curiosity about behavioural differences between the sexes undoubtedly predates recorded history, little efforts have been made to uncover the molecular basis of male and female courtship. The brain and nervous system functions that underlie sex-specific behaviour are of obvious importance to all animals including humans. To understand behaviour related to sex it is important to distinguish those aspects that are controlled genetically. The isolation and analysis of Drosophila mutants with altered sexual orientation lead to the identification of novel branches in the sex-determination cascade, which govern the sexually dimorphic development of the nervous system.

Animals↗
PubMed2004

A pea chloroplast translation elongation factor that is regulated by abiotic factors.

We report the cloning and characterization of both the cDNA (tufA) and genomic clones encoding for a chloroplast translation elongation factor (EF-Tu) from pea. The analysis of the deduced amino acids of the cDNA clone reveals the presence of putative transit peptide sequence and four GTP binding domains and two EF-Tu signature motifs in the mature polypeptide region. Using in vivo immunostaining followed by confocal microscopy pea EF-Tu was localized to chloroplast. The steady state transcript level of pea tufA was high in leaves and not detectable in roots. The expression of this gene is stimulated by light. The differential expression of this gene in response to various abiotic stresses showed that it is down-regulated in response to salinity and ABA and up-regulated in response to low temperature and salicylic acid treatment. These results indicate that regulation of pea tufA may have an important role in plant adaptation to environmental stresses.

Base Sequence↗
PubMed2004

Rare male mating advantage for inversion karyotype in Drosophila ananassae.

These experiments were conducted to study frequency-dependent sexual selection on the alpha inversion in the left arm of the second chromosome (2L) in Drosophila ananassae. Two different strains, ST/ST-standard gene arrangement and AL/AL-alpha inversion in 2L were used. Female-choice experiments were carried out in five different male ratios. Two different methods of observation have been employed, one in which copulating pairs are aspirated out and the other, in which pairs are not removed. Results were analyzed by chi(2) tests, and log odds plus regression analyses. Regression analyses revealed the presence of one-sided rare male mating advantages for AL/AL males. Preferential mating is present within the strain having AL/AL karyotype. The minority male advantage and preferential mating found in the AL/AL strain are different components of mating success. ANOVA fails to show any significant difference between the outcomes of rare-male experiments using these two different methods.

Analysis of Variance↗
PubMed2004

Tritrichomonas foetus induces apoptotic cell death in bovine vaginal epithelial cells.

Tritrichomonas foetus is a serious veterinary pathogen, causing bovine trichomoniasis, a sexually transmitted disease leading to infertility and abortion. T. foetus infects the mucosal surfaces of the reproductive tract. Infection with T. foetus leads to apoptotic cell death of bovine vaginal epithelial cells (BVECs) in culture. An affinity-purified cysteine protease (CP) fraction yielding on sodium dodecyl sulfate-polyacrylamide gel electrophoresis a single band with an apparent molecular mass of 30 kDa (CP30) also induces BVEC apoptosis. Treatment of CP30 with the protease inhibitors TLCK (Nalpha-p-tosyl-l-lysine chloromethyl ketone) and E-64 [l-trans-epoxysuccinyl-leucylamide-(4-guanido)-butane] greatly reduces induction of BVEC apoptosis. Matrix-assisted laser desorption ionization-time-of-flight MALDI-TOF mass spectrometry analysis of CP30 reveals a single peak with a molecular mass of 23.7 kDa. Mass spectral peptide sequence analysis of proteolytically digested CP30 reveals homologies to a previously reported cDNA clone, CP8 (D. J. Mallinson, J. Livingstone, K. M. Appleton, S. J. Lees, G. H. Coombs, and M. J. North, Microbiology 141:3077-3085, 1995). Induction of apoptosis is highly species specific, since the related human parasite Trichomonas vaginalis and associated purified CPs did not induce BVEC death. Fluorescence microscopy along with the Cell Death Detection ELISA(PLUS) assay and flow cytometry analyses were used to detect apoptotic nuclear condensation, DNA fragmentation, and changes in plasma membrane asymmetry in host cells undergoing apoptosis in response to T. foetus infection or incubation with CP30. Additionally, the activation of caspase-3 and inhibition of cell death by caspase inhibitors indicates that caspases are involved in BVEC apoptosis. These results imply that apoptosis is involved in the pathogenesis of T. foetus infection in vivo, which may have important implications for therapeutic interference with host cell death that could alter the course of the pathology in vivo.

Animals↗
PubMed2004

Antithrombotic therapies for stroke prevention in atrial fibrillation.

Atrial fibrillation (AF) is now regarded as the arrhythmia for which patients are hospitalized the most frequently, an arrhythmia that is responsible for significant morbidity and mortality. Of particular importance is that the arrhythmia is associated with a significant incidence of thromboembolism which may induce disabling and incapacitating strokes, sometimes fatal. In the past, it was thought that in patients with AF restoration and maintenance of sinus rhythm prevent the development of strokes, a presumption that has not been vindicated by controlled clinical trials. On the other hand, over many decades, it has been established that appropriate anticoagulation especially with warfarin can reduce stroke rate in nonvalvular AF by about 70%, and mortality by 26%. Aspirin reduces stroke rate by 26%, mortality by about 10%. Thus, in AF oral anticoagulants have become the focal point of therapy for the prevention of strokes and the safety and efficacy of such a therapy has been established by controlled clinical trials; moreover, the subsets of patients with AF in whom anticoagulation is mandatory have been defined on the basis of defined risk factors. Warfarin is now the anticoagulant of choice although its limitations are considerable in terms of drug-drug interactions, narrow range of therapeutic index requiring strict monitoring of intensity of anticoagulation, among other limitations which influence compliance of therapy with the agent. In this review, the continuing role of warfarin in the prevention of stroke in patients with AF is discussed as a background for the development of newer anticoagulants. The issue is of particular importance in the older patients, in whom the development of safer antithrombotic therapies remain a major challenge. In this context, the potential role of the direct thrombin inhibitors hold promise for the future and the evolving data on leading compounds of this class which may be competitive with warfarin are discussed.

Aged↗
PubMed2003

Molecular characterization of a nuclear topoisomerase II from Nicotiana tabacum that functionally complements a temperature-sensitive topoisomerase II yeast mutant.

We have successfully expressed enzymatically active plant topoisomerase II in Escherichia coli for the first time, which has enabled its biochemical characterization. Using a PCR-based strategy, we obtained a full-length cDNA and the corresponding genomic clone of tobacco topoisomerase II. The genomic clone has 18 exons interrupted by 17 introns. Most of the 5' and 3' splice junctions follow the typical canonical consensus dinucleotide sequence GU-AG present in other plant introns. The position of introns and phasing with respect to primary amino acid sequence in tobacco TopII and Arabidopsis TopII are highly conserved, suggesting that the two genes are evolved from the common ancestral type II topoisomerase gene. The cDNA encodes a polypeptide of 1482 amino acids. The primary amino acid sequence shows a striking sequence similarity, preserving all the structural domains that are conserved among eukaryotic type II topoisomerases in an identical spatial order. We have expressed the full-length polypeptide in E. coli and purified the recombinant protein to homogeneity. The full-length polypeptide relaxed supercoiled DNA and decatenated the catenated DNA in a Mg(2+)- and ATP-dependent manner, and this activity was inhibited by 4'-(9-acridinylamino)-3'-methoxymethanesulfonanilide (m-AMSA). The immunofluorescence and confocal microscopic studies, with antibodies developed against the N-terminal region of tobacco recombinant topoisomerase II, established the nuclear localization of topoisomerase II in tobacco BY2 cells. The regulated expression of tobacco topoisomerase II gene under the GAL1 promoter functionally complemented a temperature-sensitive TopII(ts) yeast mutant.

Amino Acid Sequence↗
PubMed2002

Cloning and characterization of a cell cycle-regulated gene encoding topoisomerase I from Nicotiana tabacum that is inducible by light, low temperature and abscisic acid.

We have cloned a full-length 2874-bp cDNA coding for tobacco topoisomerase I, with an ORF of 2559 bp encoding a protein of 852 amino acids with a calculated molecular mass of 95 kDa and an estimated pI of 9.51. The deduced amino acid sequence shows homology to other eukaryotic topoisomerases I. Tobacco topoisomerase I was over-expressed in Escherichia coli, and the purified recombinant protein was found to relax both positively and negatively super-coiled DNA in the absence of the divalent cation Mg(2+)and ATP. These characteristic features indicate that the tobacco enzyme is a type I topoisomerase. The recombinant protein could be phosphorylated at (a) threonine residue(s) by protein kinase C. However, phosphorylation did not cause any change in its enzymatic activity. The genomic organization of the topoisomerase I gene revealed the presence of 8 exons and 7 introns in the region corresponding to the ORF and one intron in the 3' UTR region. Transcript analysis using RT-PCR showed basal constitutive expression in all organs examined, and the gene was expressed at all stages of the cell cycle--but the level of expression increased during the G1-S phase. The transcript level also increased following exposure to light, low-temperature stress and abscisic acid, a stress hormone.

Abscisic Acid↗
PubMed2002

Synthesis and preliminary characterization of a novel antiarrhythmic compound (KB130015) with an improved toxicity profile compared with amiodarone.

Recent developments in antiarrhythmic therapy have indicated that the best approach to pharmacologically controlling supraventricular arrhythmias and life-threatening ventricular tachyarrhythmias is by prolonging cardiac repolarization rather than by blocking conduction. In this context, amiodarone has emerged as the most potent compound, but its universal use has been limited by its toxicity profile. There are data to suggest that an important component of amiodarones antiarrhythmic action might be mediated via inhibition of thyroid hormone action in the heart. Therefore, a new series of carboxymethoxybenzoyl and benzyl derivatives of benzofuran has been prepared and evaluated as thyroid hormone receptor antagonists. Within this series, 2-methyl-3-(3,5-diiodo-4-carboxymethoxybenzyl)benzofuran KB130015 (7) was found to reveal the most promising in vitro data. It inhibits the binding of (125)I-T(3) to the human thyroid hormone receptors (hThR) alpha(1) and beta(1). T(3)-Antagonism was confirmed in reporter cell assays employing CHOK1 cells (Chinese hamster ovary cells) stably transfected with hThR alpha(1) or hThR beta(1) and an alkaline phosphatase reporter gene downstream a thyroid response element. The derived IC(50) values were 2.2 microM for hThR alpha(1) and 4.1 microM for hThR beta(1). Compound 7 was selected for further characterization of chronic effects on ventricular papillary muscle by transmembrane electrophysiology after daily intraperitoneal injection of the ligand (40 mg/kg body weight) in guinea pigs. Compound 7 was found to prolong the action potential duration at 90% (APD(90)) repolarization time (219 +/- 22 ms, control: 186 +/- 9 ms, p < 0.01) without exhibiting any reverse rate dependency of action in a manner similar to that of amiodarone. In general, preliminary tolerance experiments with 7 demonstrated an improved safety profile compared to that of amiodarone. In summary, 7 appears to be less toxic than amiodarone while maintaining its electrophysiologic properties consistent with antiarrhythmic activity. Its potential antiarrhythmic actions warrant further investigations.

Action Potentials↗
PubMed2001

Cloning and expression of a nuclear encoded plastid specific 33 kDa ribonucleoprotein gene (33RNP) from pea that is light stimulated.

We report the cloning and sequencing of both cDNA and genomic DNA of a 33 kDa chloroplast ribonucleoprotein (33RNP) from pea. The analysis of the predicted amino acid sequence of the cDNA clone revealed that the encoded protein contains two RNA binding domains, including the conserved consensus ribonucleoprotein sequences CS-RNP1 and CS-RNP2, on the C-terminus half and the presence of a putative transit peptide sequence in the N-terminus region. The phylogenetic and multiple sequence alignment analysis of pea chloroplast RNP along with RNPs reported from the other plant sources revealed that the pea 33RNP is very closely related to Nicotiana sylvestris 31RNP and 28RNP and also to 31RNP and 28RNP of Arabidopsis and spinach, respectively. The pea 33RNP was expressed in Escherichia coli and purified to homogeneity. The in vitro import of precursor protein into chloroplasts confirmed that the N-terminus putative transit peptide is a bona fide transit peptide and 33RNP is localized in the chloroplast. The nucleic acid-binding properties of the recombinant protein, as revealed by South-Western analysis, showed that 33RNP has higher binding affinity for poly (U) and oligo dT than for ssDNA and dsDNA. The steady state transcript level was higher in leaves than in roots and the expression of this gene is light stimulated. Sequence analysis of the genomic clone revealed that the gene contains four exons and three introns. We have also isolated and analyzed the 5' flanking region of the pea 33RNP gene.

Amino Acid Sequence↗
PubMed2001

What niche will newer class III antiarrhythmic drugs occupy?

The decline in the use of sodium channel blockers has led to an expanding use of b-blockers and complex class III agents such as sotalol and amiodarone for controlling cardiac arrhythmias. Success with these agents in the context of their side effects has spurred the development of compounds with simpler ion channel-blocking properties with less complex adverse reactions. The resulting so-called pure class III agents were found to have antifibrillatory effects in atrial fibrillation (AF) and flutter, as well as in ventricular tachyarrhythmias. Pure class III compounds are effective in inducing acute chemical conversion of AF, in preventing paroxysmal AF, and in maintaining sinus rhythm in patients with persistent AF restored to sinus rhythm. Examples of such compounds are dofetilide, which selectively blocks IKr, and ibutilide, available only as an intravenous agent, which blocks the IKr and augments the inactivated Na+ current in atrial myocytes. Dofetilide and ibutilide have been introduced into clinical practice. Azimilide is the first of the class III agents that blocks both components (IKr and IKs) of the delayed rectifier current, which may confer certain electrophysiologic advantages. The potential therapeutic niche of ibutilide, dofetilide, and azimilide in the control of cardiac arrhythmias forms the basis of this review.

Anti-Arrhythmia Agents↗
PubMed2001

Female remating in Drosophila ananassae: bidirectional selection for remating speed.

In Drosophila ananassae, artificial selection was carried out for fast and slow remating speed for 10 generations. Response to selection resulted in rapid divergence in remating time in each of two replicates of both fast and slow lines. There were significant differences in mean remating time in females among fast, slow, and control lines. Regression coefficients for both fast and slow lines are significantly different from zero. The realized heritability over 10 generations of selection is from 0.26 to 0.33 for two replicates of fast line and from 0.23 to 0.27 for two replicates of slow line. These findings suggest that female remating time in D. ananassae is under polygenic control. Remating frequency of females showed a correlated response in both fast and slow lines. At generation 10, correlated response to selection was also investigated. Mating propensity of D. ananassae of fast and slow lines was observed in an Elens-Wattiaux mating chamber. Fifteen pairs per test showed that on the average, the fast lines (11.20, 11.60) were more successful in mating than those of slow (6.40, 5.60) and control (8.00) lines. Productivity of once-mated females was measured in terms of number of progeny produced per female and the results of productivity analysis indicate that females of fast lines (157.83, 130.83) produced more progeny compared with slow (72.70, 85.83) and control (109.23) lines.

Animals↗