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Biomedical subjects

R Dixit

Publications and source records attributed to R Dixit.

At least 19 recordsLinked to original sources
PubMed2005

Narrowing of the preprophase microtubule band is not required for cell division plane determination in cultured plant cells.

In most higher-plant cells, cortical microtubules form a tightly focused preprophase band (PPB) that disappears with the onset of prometaphase, but whose location defines the future location of the cell plate at the end of cytokinesis. It is unclear whether the PPB microtubules themselves designate the precise area where the cell plate will insert, or rather if these microtubules are responding to a hierarchical signal(s). Here we show that narrowing of the microtubules within the PPB zone is not necessary for proper division plane determination. In cultured tobacco BY-2 cells in which PPB microtubules are depolymerized, the phragmoplast can still accurately locate and insert at the proper site. The data do not support a role for PPB microtubule narrowing in focusing the signal that is used later by the phragmoplast to position the cell plate; rather, proper phragmoplast positioning is more likely a consequence of a non-microtubule positional element. Although the PPB microtubules do not directly mark the division site, we show that they are required for accurate spindle positioning, an activity that presets the future growth trajectory of the phragmoplast and is necessary for insuring high-fidelity cell plate positioning.

Benzamides↗
PubMed2002

Spatio-temporal relationship between nuclear-envelope breakdown and preprophase band disappearance in cultured tobacco cells.

Cell division involves the coordinated progression of karyokinesis and cytokinesis, which is accomplished by communication between the nucleus and the cytoplasm. We have utilized green-fluorescent-protein technology to generate a line of tobacco 'Bright Yellow 2' (BY-2) cells labeled for both microtubules and the nuclear envelope. This cell line allowed us to use living cells to investigate the relationship between nuclear-envelope breakdown and preprophase band disappearance with high spatial and temporal resolution. Our observations demonstrate that nuclear-envelope breakdown always precedes preprophase band disappearance in BY-2 cells. In addition, the rate of preprophase band disappearance, and the attenuation of perinuclear microtubule fluorescence, correlates with the proximity of the nucleus to the preprophase band site. These results indicate the presence of communication between the nucleus and the preprophase band and suggest a causal relationship between nuclear-envelope breakdown and preprophase band disappearance.

Cell Division↗
PubMed2001

The brassica MIP-MOD gene encodes a functional water channel that is expressed in the stigma epidermis.

In crucifers, the ability of the stigma to differentially modulate hydration of pollen grains, depending on whether the pollen is recognized to be compatible or incompatible, represents a crucial stage in pollination. Our recent analysis of the mod mutation of Brassica, which results in a breakdown of the self-incompatibility response, led to the isolation of a gene linked to the MOD locus which is expressed at low levels in mod mutants. The gene is predicted to encode a plasma membrane-localized aquaporin-like protein and has been designated MIP-MOD. We utilized reporter gene analysis to demonstrate that the MIP-MOD promoter is active in Brassica papillar cells as well as in some vegetative tissues. The encoded protein is also likely to be plasma membrane-localized based on the observation that all plasma membrane-intrinsic aquaporin-like proteins in Brassica leaves are enriched in plasma membrane fractions. The MIP-MOD protein results in a low but measurable enhancement in osmotic water permeability of Xenopus oocytes and hence represents a functional aquaporin. The results are consistent with the notion that MIP-MOD is involved in the regulation of water transport across the stigma epidermal cell membrane.

Animals↗
PubMed2001

Application of rat hepatocyte culture to predict in vivo metabolic auto-induction: studies with DFP, a cyclooxygenase-2 inhibitor.

The drug candidate DFP [5,5-dimethyl-3-(2-isopropoxy)-4-(4-methanesulfonylphenyl)-2(5H)-furanone] is a selective cyclooxygenase-2 inhibitor under evaluation for analgesic and anti-inflammatory therapy. The in vitro metabolic pathways (rat microsomes) involve hydroxylation of the isopropyl side chain at either of two positions, the methyl or the methine, thus producing a hydroxylated metabolite (DFHP) or a dealkylated metabolite (DFH). DFH formation was the major pathway. Using hepatic microsomes from rats treated with agents that induce specific CYP isozymes, it was shown that the dexamethasone-inducible rat CYP3A isozyme(s) play a major role in DFH formation. The roles of CYP3A1 and -3A2 were confirmed with genetically engineered rat CYP enzymes. The potential for induction of rat CYP3A by DFP was evaluated by incubating DFP in rat hepatocyte cultures and measuring the CYP3A levels. Both CYP3A immunoreactive protein and enzyme activity were induced in a dose-dependent manner. The induction was confirmed in vivo by dosing rats with DFP at 100 mg/kg for 4 days. Microsomes prepared from the excised livers showed that DFP gave approximately 55% of the induction observed with dexamethasone, as determined by Western blot. In vitro metabolic auto-induction of DFP was assessed by measuring the metabolism of DFP in hepatocytes treated with DFP. DFH formation was significantly enhanced in the DFP-treated cells. In vivo, treating rats with DFP at doses of 10 to 100 mg/(kg.day) for 13 weeks indicated that DFP induced its own metabolism. The C(max) and plasma drug area under the curve values during the thirteenth week were significantly lower than that on the first day, and the effect was dose-dependent.

Alkylation↗
PubMed2001

Anti-mosquito ovary antibodies reduce the fecundity of Anopheles stephensi (Diptera:Insecta).

Rabbit antibodies to five antigens (AJ** 29, 35, 43, 64, and 80 kDa) derived from the ovaries of Anopheles stephensi tended to reduce the number of eggs produced. Ingestion of anti-mosquito ovary antibodies did not show a detectable effect on the mortality of mosquitoes. Antisera raised against An. stephensi ovaries showed cross-reactivity in other tissues and in the ovaries of other Anopheles spp. by Western blotting. The results indicate that anti-mosquito ovary antibodies have the potential to disrupt the reproductive physiology of mosquitoes, and indicate the need for further studies with target antigens.

Animals↗
PubMed2000

Post-transcriptional maturation of the S receptor kinase of Brassica correlates with co-expression of the S-locus glycoprotein in the stigmas of two Brassica strains and in transgenic tobacco plants.

The S-locus-encoded S receptor kinase (SRK) is an intrinsic plasma membrane protein that is viewed as the primary stigma determinant of specificity in the self-incompatibility response of Brassica spp. We analyzed two self-compatible mutant strains that express low levels of the S-locus glycoprotein (SLG), a cell wall-localized protein also encoded at the S locus that is coordinately expressed with SRK. We found that mutant stigmas synthesized wild-type levels of SRK transcripts but failed to produce SRK protein at any of the developmental stages analyzed. Furthermore, SRK was shown to form aberrant high-molecular mass aggregates when expressed alone in transgenic tobacco (Nicotiana tabacum) plants. This aggregation was prevented in tobacco plants that co-expressed SRK and SLG, but not in tobacco plants that co-expressed SRK and SLR1, an SLG-related secreted protein not encoded at the S locus. In analyses of protein extracts under reducing and non-reducing conditions, evidence of intermolecular association was obtained only for SLG, a fraction of which formed disulfide-linked oligomers and was membrane associated. The data indicate that, at least in plants carrying the S haplotypes we analyzed, SRK is an inherently unstable protein and that SLG facilitates its accumulation to physiologically relevant levels in Brassica stigmas.

Brassica↗
PubMed2000

Comparative study of visceral and parietal pleural biopsy in the etiological diagnosis of pleural diseases.

OBJECTIVE: The present study was planned to evaluate the efficacy and diagnostic reliability of conoctional parietal pleural biopsy to a technique of visceral pleural biopsy. METHOD: Study comprises of 54 diagnosed cases of pleural effusion and after establishing the clinical diagnosis for probable etiological causes. Then parietal pleural biopsy using absents punch biopsy needle and vesceral pleural biopsy using Prabhudesai et al technique was taken in all these patients. Size of the tissue yield; percentage of biopsies; diagnostic yield and sensitivity for these two techniques were compared. RESULTS: A definitive etiological diagnosis could be reached in 52 out of 54 patients on the basis of pleural biopsy (33 tuberculous, 16 malignant and 3 pyogenic), 23 (69.7%) tuberculous effusion patients were diagnosis by visceral pleural biopsy and 14 (42.4%) by parietal pleural biopsy out of 33 diagnosed tuberculous effusion cases. While for the 16 malignant effusions the visceral pleural biopsy showed suggestive histological change in 13 (81.25%) patients and the parietal pleural biopsy in seven (43.8%) with five (31.25%) of these patients being positive by both. All three pyogenic effusions showed only nonspecific inflammatory change in both pleurae. CONCLUSION: The mean size of biopsy sample obtained with modified Prabhudesai et al technique was significantly larger than that of the parietal pleural biopsy with Abrams punch (4.85 mm2 V/s 2.5 mm2 with P < 0.01). Adequate pleural tissue was identifiable in 94.4% and 90.7% of cases, respectively. The modified Prabhudesai et al technique proved to be effective safe and easily learnt. Visceral pleural sampling using this technique is a definite superior addition to the present diagnostic armamentarium of an idiopathic pleural effusion and its routine application together with parietal pleural biopsy will help to establish a definitive diagnosis in majority of patients with idiopathic pleural effusions.

Adolescent↗
PubMed1999

Organization and post-transcriptional processing of the psb B operon from chloroplasts of Populus deltoides.

Chloroplast genes are typically organized into polycistronic transcription units that give rise to complex sets of mono- and oligo-cistronic overlapping RNAs through a series of processing steps. The psbB operon contains genes for the PSII (psbB, psbT, psbH) and cytochrome b(6)f (petB and petD) complexes which are needed in different amounts during chloroplast biogenesis. The functional significance of gene organization in this polycistronic unit, containing information for two different complexes, is not known and is of interest. To determine the organization and expression of these complexes, studies have been carried out on crop plants by different groups, but not much information is known about trees. We present the nucleotide sequences of PSII genes and RNA profiles of the genes located in the psbB operon from Populus deltoides, a tree species. Although the gene organization of this operon in P. deltoides is similar to that in other species, a few variations have been observed in the processing scheme.

Amino Acid Sequence↗
PubMed1999

Hepatitis E infection in children: study of an outbreak.

BACKGROUND: Hepatitis E virus (HEV) is responsible for most of the hepatitis epidemics in the developing world and it frequently affects young adults. Therefore, common perception is that it does not affect children. METHODS: A group of 20 school children (13 years old) were possibly exposed to hepatitis E virus infection during a 2 day trekking trip. Epidemiological and clinical information was correlated to the presence of the hepatitis E virus genome and antibodies to HEV structural and non-structural proteins found in the blood of the children, using polymerase chain reaction and line immunoassay techniques. RESULTS: Ten children developed icteric hepatitis, seven prodrome-like illness without jaundice while three remained asymptomatic. Immunoglobulin M (IgM) antibodies to open reading frame (ORF)2 protein (pORF2) were detected in all 19 children tested, whereas 11 and 10 of the children were positive for IgM antibodies against ORF1 (pORF1) and ORF3 (pORF3) proteins, respectively. The rate of HEV infection was found to be 85%. Viraemia was observed in 11 children and was present in four of the seven anicteric patients (55%) compared with six of the nine (66%) icteric patients. One child without any symptom also had viraemia. CONCLUSIONS: The data obtained indicate a high susceptibility of children for HEV infection and a frequently prolonged viraemia in those infected.

Adolescent↗
PubMed1999

A method for estimating and testing area under the curve in serial sacrifice, batch, and complete data designs.

The extent of drug availability is often measured by the area under the concentration-time curve. In animal studies, experimental constraints can limit the number of observations available on each animal. Estimation of area under the curve and its standard error are straightforward when each animal is measured at each time point. Bailer and Nedelman et al., have described techniques for estimating the area under the curve and its standard error when each animal is measured once. Yeh has described a technique for the hybrid case where animals are measured more than once, but not at all time points. We describe a method for estimating area under the curve and its standard error which is applicable to all three types of designs. We give formulas for testing treatment differences, including dose trends and dose proportionality, in area under the curve for designs containing an arbitrary number of treatments. A jackknife estimator is also described.

Analysis of Variance↗
PubMed1999

Diet, caloric restriction, and the rodent bioassay.

The diet can significantly alter the results of toxicity and carcinogenicity studies. Ad libitum (AL) overfeeding of excessive calories to sedentary adult rodents is one of the most poorly controlled variables affecting the current rodent bioassay. AL-overfed rodents develop an early onset of adverse metabolic events, endocrine-disruptive degenerative diseases, and tumors that result in early morbidity and mortality. AL food consumption is extremely variable, but has a strong correlation with adult body weight, obesity, and survival. AL feeding of diets with modified protein, fiber, and energy content are not as effective as simple, moderate dietary (caloric) restriction (DR) in controlling these study variables. Moderate DR (70-75% of adult AL) is operationally simple and controls adult body weights, prevents obesity, and improves health and survival by reducing or delaying diet-related endocrine, renal, and cardiac diseases. Moderate DR provides a uniform rodent model, increases treatment exposure time, and increases the statistical sensitivity of these chronic bioassays to detect true treatment effects. Feeding a balanced diet by a moderate DR regimen of 70-75% of the maximum, unrestricted adult AL food intake is recommended for conducting well-controlled toxicity and carcinogenicity studies.

Animals↗
PubMed1999

Adaptive role of caloric intake on the degenerative disease processes.

Carcinogenicity and aging are characterized by a set of complex endpoints, which appear as a series of molecular events. Many of these events can be modified by caloric intake. Since most of these processes determine an organism's ability to cope with various environmental stressors, it is not surprising that a relationship (in the presence of a constant nutrient density) exists between caloric intake and time-to-tumor and/or life span. Our studies have clearly shown that generally, the greater the caloric intake, the greater the body weight, the higher the incidence of spontaneous tumor occurrence, the greater the susceptibility to chemical carcinogens, and the shorter the life span. It is also recognized that variables other than body weight influence the life span and carcinogenesis. We have focused our attention on the questions of how and to what extent caloric intake modifies those homeostatic processes believed to be critical in determining the ability of an organism to cope with endogenous and exogenous stresses such as chemical, physical, and biological carcinogens. The response of an organism to its environment can be divided into four categories--physiological, metabolic, molecular, and cellular. We have found that, from a physiological perspective, decreasing caloric intake causes body temperature in rodents to be decreased by 0.5 to 1.8 degrees C and water consumption to be increased by 80%, as is running activity. However, metabolic output per gram of lean body mass is not altered. Reproductive capacity declines, whereas the ECG waveform is preserved as caloric intake decreases. Alterations in these and other physiological functions suggests that energy intake serves as a signal to up-regulate or down-regulate functions related to the flight-or-fight response observed in placental mammals. A number of key metabolic pathways are altered as a function of lowered caloric intake, even though the rate of food consumption per gram of lean body mass remains steady during body weight decreases caused by decreasing caloric intake. Pharmacological compartmentalization, however, is altered. As caloric intake declines, changes occur in the expression of a number of drug-metabolizing enzymes, with the most striking effect seen in sex-specific growth hormones and liver-dependent phase I and phase II enzymes. Additionally, oxidative stress (free-radical and mediated damage to macromolecules) appears to decrease as a function of reduced caloric intake. A number of molecular processes also change with changes in energy consumption. Our studies have shown that, regardless of the source and nature of DNA damage, DNA repair is better preserved and/or enhanced when caloric consumption decreases. In addition, the fidelity of DNA replication increases and oncogene expression is stabilized, P53 gene expression is increased, and apoptosis is elevated by up to 500% with decreased caloric intake. At the cellular level, cell proliferation is decreased in direct proportion to lower energy intake in some but not all tissues. Studies have also shown an enhancement in immune capacity, changes in IGF1, and accelerated rates of wound healing proportionate to declines in energy consumption. Our most recent findings, however, have shown that the benefits associated with decreases in caloric intake only occur in the presence of sufficient nutrient quality and density. In the absence of proper nutrition, however, sensitivity to carcinogens and toxic substances appears to be enhanced. These findings are supported by independent studies. These observations have led us to conclude that, in certain organisms, when caloric intake is decreased, there is an up-regulation of those processes that modulate the responses to a wide range of environmental stressors. This response allows for a better survival rate and a down-regulation of reproductive activity. It is our belief that, during periods of environmental stress, these systems may be essential to perpetu

Adaptation, Physiological↗