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Biomedical subjects

A Das

Publications and source records attributed to A Das.

At least 235 records · Page 13Linked to original sources
PubMed1995

Mating propensity of Indian Drosophila melanogaster populations with D. simulans: a nonadaptive latitudinal cline.

Crosses were investigated between a single strain of Drosophila simulans and 28 natural Indian populations of D. melanogaster. In each case, a mass culture and 10 isofemale lines of D. melanogaster were studied. Crosses were much easier between D. melanogaster females and D. simulans males than in the reciprocal case. Also, hybrid offspring were easier to obtain by using D. melanogaster flies (either males or females) from isofemale lines than from mass cultures. Finally, the crossability, estimated by progeny production, showed a clear-cut latitudinal cline: hybrids were easier to obtain with D. melanogaster populations from higher latitudes. As D. simulans does not occur in India, this cline does not reflect an evolutionary interaction between the two sibling species.

Adaptation, Physiological↗
PubMed1995

A silicon micromachined device for use in blood cell deformability studies.

An application of silicon micromachining to the analysis of blood cell rheology is described. The system, based upon a micromachined flow cell, provides a specific measurement of each cell in a statistically significant population in terms of both flow velocity profile and an index of cell volume while the cells flow through an array of microchannels. The rationale, design, and fabrication of the silicon micromachined flow cell is discussed. Interrelated considerations determining the design of the associated fluidic, mechanical, imaging, and real-time image analysis subsystems are examined. Sample data comparing normal and iron deficiency anaemic blood are presented to illustrate the potential of this technique.

Blood Cells↗
PubMed1995

Receptive field expansion in adult visual cortex is linked to dynamic changes in strength of cortical connections.

1. Receptive field (RF) sizes of neurons in adult primary visual cortex are dynamic, expanding and contracting in response to alternate stimulation outside and within the RF over periods ranging from seconds to minutes. The substrate for this dynamic expansion was shown to lie in cortex, as opposed to subcortical parts of the visual pathway. The present study was designed to examine changes in cortical connection strengths that could underlie this observed plasticity by measuring the changes in cross-correlation histograms between pairs of primary visual cortex neurons that are induced to dynamically change their RF sizes. 2. Visually driven neural activity was recorded from single units in the superficial layers of primary visual cortex in adult cats, with two independent electrodes separated by 0.1-5 mm at their tips, and cross-correlated on-line. The neurons were then conditioned by stimulation with an "artificial scotoma," a field of flashing random dots filling the region of visual space around a blank rectangle enclosing the RFs of the recorded neurons. The neuronal RFs were tested for expansion and their visually driven output again cross-correlated. After this, the neurons were stimulated vigorously through their RF centers to induce the field to collapse, and the visually driven output from the collapsed RFs was again cross-correlated. Cross-correlograms obtained before and after conditioning, and after RF collapse, were normalized by their flanks to control for changes in peak size due solely to fluctuations in spike rate. 3. A total of 37 pairs of neurons that showed distinct cross-correlogram peaks, and whose RF borders were clearly discernible both before and after conditioning, were used in the final analysis. Of these neuron pairs, conditioning led to a clear expansion of RF boundaries in 28 pairs, whereas in 9 pairs the RFs did not expand. RFs that did expand showed no significant shifts in their orientation preference, orientation selectivity, or ocularity. 4. When the RFs of a pair of neurons expanded with conditioning, the area of the associated flank-normalized cross-correlogram peaks also increased (by a factor ranging from 0.84 up to 3.5). Correlograms returned to their preconditioning values when RFs collapsed.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Effects of sex steroids on the concentrations of some brain neurotransmitters in male and female rats: some new observations.

Concentrations of some neurotransmitters, viz. noradrenaline (NA), 5-hydroxytryptamine (5-HT), dopamine (DA), histamine (H) and gamma aminobutyric acid (GABA) in a part of brain consisting of medulla, pons, mid brain, thalamus and hypothalamus were measured in ovariectomized (OVx), intact (+Te) and castrated male (Tex) rats both without injecting estrogen (E) or E and progesterone (P) as well as after E and E+P administration. Some effects, (which, as far as we are aware of) have not been previously reported, were noted (in addition to other already documented observations). These include: (i) castration in males causes a fall of the level of GABA, NA, 5-HT and DA, (ii) E therapy also causes fall of the levels of GABA, NA and 5-HT and thus E therapy produces similar results like those of bilateral orchidectomy, (iii) P therapy not only reverses the fall of (GABA) but raises it more than the normal value, (iv) P therapy, it appears (although faintly), retrieve to some extent the fall of NA level due to E therapy, (v) Like the OVx rats, castrated as well as intact rats also showed a fall in the 5-HT level with E treatment but showed a rise when treated by E followed by P, (vi) In between the castrated males and castrated females, the concentrations of all these brain neurotransmitters differ. The probable significances have been discussed.

Animals↗
PubMed1994

Biosynthesis, export and processing of a 45 kDa protein detected in membrane clefts of erythrocytes infected with Plasmodium falciparum.

During its asexual life cycle, the human malaria parasite Plasmodium falciparum exports numerous proteins beyond its surface to its host erythrocyte. We have studied the biosynthesis, processing and export of a 45 kDa parasite protein resident in membrane clefts in the erythrocyte cytoplasm. Our results indicate that this cleft protein is made as a single tightly membrane-bound 45 kDa polypeptide in ring- and trophozoite-infected erythrocytes (0-36 h in the life cycle). Using ring/trophozoite parasites released from erythrocytes, the 45 kDa protein is shown to be efficiently transported to the cell surface. This export is specifically blocked by the drug brefeldin A, and at 15 and 20 degrees C. These results indicate that transport blocks seen in the Golgi of mammalian cells are conserved in P. falciparum. Further, the newly synthesized 45 kDa protein passes through parasite Golgi compartments before its export to clefts in the erythrocyte. In mid-to-late-ring-infected erythrocytes, a fraction of the newly synthesized 45 kDa protein is processed to a second membrane-bound phosphorylated 47 kDa protein. The t1/2 of this processing step is about 4 h, suggesting that it occurs subsequent to protein export from the parasite. Evidence is presented that, in later trophozoite stages (24-36 h), the exported 45 and 47 kDa proteins are partially converted into soluble molecules in the intraerythrocytic space. Taken together, the results indicate that the lower eukaryote P. falciparum modulates a classical secretory pathway to support membrane export beyond its plasma membrane to clefts in the erythrocyte. Subsequent to export, phosphorylation and/or conversion into a soluble form may regulate the interactions of the 45 kDa protein with the clefts during parasite development.

Animals↗
PubMed1994

Control of transcription processivity in phage lambda: Nus factors strengthen the termination-resistant state of RNA polymerase induced by N antiterminator.

During transcription of phage lambda early operons, the N gene product alters host RNA polymerase (RNAP) so that transcription proceeds through multiple stop signals. Here, we reproduce the essence of N activity with purified components in synthetic transcription units that contain lambda pL promoter and the N-recognition site, nutL, followed by a variety of intrinsic terminators. We show that three host factors (NusA, NusE, and NusG) are essential for N to allow appreciable transcription through multiple terminators and that this persistent antitermination is stimulated by a fourth factor, NusB. Remarkably, in the absence of all four factors, N suppresses various terminators placed near the nut site. This basal antitermination activity of N is enhanced by NusA and is diminished by high salt and temperature. We postulate that N interacts with RNAP directly, inducing the termination-resistant state. While NusA facilitates this interaction, the other factors strengthen it sufficiently over time and distance so that RNAP bypasses multiple terminators. The dispensability of NusB for persistent antitermination in vitro, but not in vivo, raises the possibility that NusB performs two functions: it increases the stability of N antitermination complex and also counteracts an inhibitory factor in the cell.

Bacterial Proteins↗
PubMed1994

Constitutive expression of the virulence genes improves the efficiency of plant transformation by Agrobacterium.

Inducible virulence (vir) genes of the Agrobacterium tumefaciens tumor-inducing (Ti) plasmid are under control of a two-component regulatory system. In response to environmental factors (phenolic compounds, sugars, pH) VirA protein phosphorylates VirG, which in turn interacts with the promoters of other vir genes, causing induction. A mutation of virG, virGN54D (which codes for a Asn-54-->Asp amino acid change in the product), causes constitutive expression of other vir genes independent of virA. We have investigated whether providing Agrobacterium with a plasmid containing virGN54D augments the efficiency of transfer of the T-DNA (transferred DNA). For both tobacco and cotton, we observed an enhancement of transformation efficiency when the inciting Agrobacterium strain carries the virGN54D mutation. We also tested whether supplying Agrobacterium with a similar plasmid containing wild-type virG affects the efficiency of T-DNA transfer. An intermediate efficiency was observed when this plasmid was employed. Using a beta-glucuronidase (GUS) reporter gene to assess transient expression of T-DNA after transfer to tobacco and maize tissues, we observed a higher frequency of GUS-expressing foci after inoculation with Agrobacterium strains carrying virGN54D than with Agrobacterium carrying the wild-type virG. Gene-transfer efficiency to maize by an octopine strain was greatly improved upon introduction of virGN54D. Multiple copies of wild-type virG were equally effective in promoting transient expression efficiency in tobacco but were virtually ineffective in maize. We propose the use of virGN54D to improve the efficiency of Agrobacterium-mediated transformation, especially for recalcitrant plant species.

Agrobacterium tumefaciens↗
PubMed1994

Inversion polymorphism and extra bristles in Indian natural populations of Drosophila ananassae: joint variation.

Five Indian natural populations of Drosophila ananassae were analysed for chromosome inversions and the presence of individuals with extra scutellar bristles in the F1 progeny of isofemale lines initiated from naturally impregnated females. Three commonly occurring inversions were found in these populations with varying frequencies as was the number of individuals with extra bristles (e.b.). Female individuals were more often found to carry extra scutellar bristles than were males. This result reveals that polygenic loci responsible for the determination of e.b. are widespread in Indian natural populations of D. ananassae. A significant positive correlation between the inversion frequency and the number of individuals with e.b. was detected in the isofemale lines of all the five populations. The 2L inversion, alpha, was found to be closely associated with individuals with the e.b. phenotype. The observed results are compared with earlier results obtained for D. melanogaster. The association of the alpha inversion with the e.b. phenotype is discussed in relation to chromosomal evolution in the melanogaster species group.

Animals↗
PubMed1994

Spectrum of reticulate flexural and acral pigmentary disorders in northern India.

Reticulate pigmentary disorders are rare in India. Only 15 cases of reticulate acropigmentation of Kitamura (RAPK) and 9 cases of Dowling-Degos disease (DDD) have been reported previously. To the best of our knowledge, there has been no earlier report of acropigmentation of Dohi. We herein describe 10 patients with various reticulate pigmentary abnormalities: 6 with RAPK, 2 with DDD, 1 with RAPK-DDD overlap, and 1 with acropigmentation of Dohi. Palmar pits and/or breaks in epidermal ridge pattern were absent in 2 of 6 patients with RAPK. A 23-year-old male patient had RAPK-DDD overlap. Periorbital pigmentation and pigmentation over the mucosal surface of the prepuce and corona of the glans penis were some unique features observed in this patient. His sister and mother had RAPK and DDD, respectively. We concluded that RAPK and DDD are varying manifestations of a single entity. Their presence in other family members probably depends on the degree of penetrance.

Adolescent↗
PubMed1994

Mutational analysis of Agrobacterium tumefaciens pTiA6 virD1: identification of functionally important residues.

Mutagenesis experiments were used to identify functionally important regions of Agrobacterium tumefaciens pTiA6 VirD1. Random mutations were introduced by using Taq polymerase in a mutagenic reaction buffer containing manganese and altered nucleotide ratios to increase errors during the polymerase chain reaction (PCR). The mutants were assayed for VirD1-, VirD2-dependent border-nicking activity in Escherichia coli harbouring a border-containing substrate plasmid. Analysis of the mutants led to the identification of a region from amino acids 45-60 that is important for VirD1 activity. This region corresponds to a previously postulated potential DNA-binding domain. Deletion mutagenesis indicated that amino acids 2-16 could be deleted without affecting VirD1 function, whereas a larger deletion, amino acids 5-27, completely inactivated VirD1.

Agrobacterium tumefaciens↗