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Biomedical subjects

T Sharma

Publications and source records attributed to T Sharma.

At least 163 records · Page 9Linked to original sources
PubMed1986

Co-cultivation of whole blood from male and female muntjacs and the cell proliferation kinetics in vitro.

A mixed blood culture (MBC) of heparinized whole blood from male and female Indian muntjac has been done using the BrdU-Hoechst-sunlight-Giemsa method to study the cell-cycle kinetics in vitro. Blood lymphocytes of both male and female muntjacs show a much shorter cell cycle time, roughly, 10-12 h for the initial but only 8 h for the subsequent cycles. There is a significant difference in the rate of cell proliferation between male and female cells. The male blood cells constitute a majority of the 'slow'-dividing cells which reach a peak at the first cycle of mitosis at 40 h, whereas a similar peak of first cycle mitosis is reached by female cells at 32 h, indicating the occurrence of a high frequency of 'fast' dividing female cells as compared to those of males. This novel sex-based differential cell proliferation kinetics is observed both in mixed and separate cultures. This type of MBC method which is free of interculture variations can be reliably used for comparative studies where two genomes can be distinguished.

Animals↗
PubMed1986

Higher incidence of spontaneous sister-chromatid exchanges (SCEs) and X-ray-induced chromosome aberrations in peripheral blood lymphocytes during pregnancy.

In vitro cultures of peripheral blood lymphocytes from human and muntjac (barking deer) females who were at an advanced stage of pregnancy (32-37 weeks pregnant women and 20-24 weeks pregnant muntjacs) showed an enhanced frequency of SCEs and X-ray-induced chromosome aberrations when compared with those of nonpregnant females. Lymphocyte cultures of nonpregnant females to which sex hormones progesterone, oestrogen and human chorionic gonadotropin (HCG) were added together exogenously also showed higher frequency of SCEs. The plausible reason(s) for such high incidence of SCEs during pregnancy is discussed.

Adult↗
PubMed1985

Characterization of G-banded chromosomes of the Indian muntjac and progression of banding patterns through different stages of condensation.

Muntjac prophase and metaphase chromosomes were G-banded following methotrexate-mediated synchronization of peripheral lymphocytes. Bands and subbands were characterized from prophase through metaphase, and the progression of band patterns from late prophase to mid-metaphase was analyzed. Extended prophase chromosomes exhibited more bands and subbands, a number of which became fused with each other, giving rise to fewer and thicker bands in the condensed metaphase chromosomes. It appeared that the dark bands condensed relatively more than the light bands. Precise delineation of the bands and subbands on extended prophase chromosomes and the usage of a proposed banding pattern nomenclature should aid in better detection and localization of induced chromosomal rearrangements with this extremely useful experimental material.

Animals↗
PubMed1984

Effects of temperature on the frequency of sister chromatid exchanges (SCEs) in peripheral blood lymphocytes of man and muntjac.

The incidence of sister chromatid exchanges (SCEs) and cell proliferation kinetics have been studied in peripheral blood lymphocytes of man and muntjac grown at 33 to 44 degrees C to gain insight into SCE formation. The frequency of SCEs increased as a function of growth temperature. At a given temperature, however, the frequency of SCEs varied with the sampling times; the early sampled cells showed fewer SCEs than did those harvested late. At 33 degrees C the frequency of SCEs was lowest and there was a marked delay in cell-cycle progression. The number of SCEs was maximum at 40 degrees C in human and 42 degrees C in muntjac. Cell proliferation was markedly affected at higher temperature and 44 degrees C was found to be intolerable for lymphocytes of both the species. It is proposed that certain temperature-dependent enzyme(s) associated with DNA replication kinetics may be involved in the formation of SCEs.

Animals↗
PubMed1984

The effect of storage of blood on the yield of X-ray-induced chromosome aberrations and spontaneous sister chromatid exchanges.

Heparinized whole blood of man and muntjac (Indian barking deer) was stored at 5, 22 and 37 degrees C for varying durations up to 168 hours and then exposed to 2.0 or 3.0 Gy of X-rays. The yield of dicentrics and other aberrations scored in first post-irradiation metaphases from lymphocytes of both man and muntjac did not vary significantly. However, a marked increase in the proportion of first division metaphases at a given sampling time due to delay in cell cycle progression was noticed in lymphocyte cultures set up from stored blood. There was a relatively higher proportion of first division metaphases in cultures of blood stored at the frequency of spontaneous SCEs was observed in lymphocyte cultures set up from stored and fresh blood.

Animals↗
PubMed1983

Reduced frequency of baseline sister chromatid exchanges in lymphocytes grown in antibiotics and serum-excluded culture medium.

Peripheral venous blood from man, muntjac, and cattle were grown in medium (1) containing different serum (human AB+/FCS/autologous), (2) without serum or antibiotics (penicillin and streptomycin), or (3) without both serum and antibiotics to investigate to what extent certain essential culture components used in in vitro mammalian cell cultures affect the incidence of spontaneous sister chromatid exchanges (SCEs). The observation that exclusion of only serum from culture medium enhanced the frequency of SCEs whereas exclusion of both serum and antibiotics, which influence the cell cycle kinetics to a great extent, exhibited the lowest frequency of SCEs reported so far for lymphocyte cultures, indicates that the frequency of so-called spontaneous SCEs usually observed in normal lymphocyte cultures grown in medium supplemented with serum and antibiotics is in fact an elevated frequency.

Animals↗
PubMed1983

Influence of age on the frequency of sister-chromatid exchanges and X-ray-induced chromosome aberrations in muntjac.

The BrdU-differential staining technique was used in a study of the frequency of sister-chromatid exchanges (SCEs) and X-ray-induced chromosome aberrations in peripheral blood lymphocytes of the same individual muntjacs. Blood was collected periodically from immediately after birth (1 day old) to the adult stage (1 year). The results showed that both the frequency of base-line SCEs and induced chromosome aberrations changed as a function of age. At a young age, the frequency of SCEs was significantly low, whereas a high frequency of chromosome aberrations was observed. But with increase in age of the individuals, an enhanced frequency of SCEs and a decreased frequency of induced chromosome aberrations were observed; and as the age advanced further, the frequencies of both SCEs and chromosomal aberrations came to a steady level.

Aging↗
PubMed1982

Asynchronous replication of constitutive heterochromatin on X chromosomes in female Mus dunni. Possible influence of facultative heterochromatin on the adjacent constitutive heterochromatin.

Euchromatin DNA of one X chromosome in mammalian females, which becomes facultatively heterochromatinized, is known to replicate asynchronously late in S phase compared to its active homologue. In the females of a pygmy mouse species Mus dunni, which has prominent segment of constitutive heterochromatin as the short arm of its submetacentric X chromosome, we have observed asynchronous replication of c-heterochromatin arm as well, predominant number of cells showing the segment associated with the facultatively heterochromatic X to be terminating later. The preferential later termination of replication of the c-heterochromatic arm on the "lyonized X" appears to be due to the influence of facultative heterochromatin on the adjacent constitutive heterochromatin.

Animals↗
PubMed1982

Evaluation of radiation-induced chromosomal aberrations in human peripheral blood lymphocytes in vitro: result of an IAEA-coordinated programme.

The results of an IAEA coordinated programme on radiation induced chromosomal aberrations in human peripheral blood lymphocytes in vitro are presented. In a master experiment, a whole blood sample from one donor was irradiated with 200 R of X-rays. Different fixation times from 46 to 82 h were used. The progression of cells into mitosis was monitored by BrdUrd incorporation. 14 investigators took part in the scoring of chromosomal aberrations. The main conclusions of this study are: (1) The mean frequencies of aberrations changed with fixation time. (2) The number of cells scored as aberrant by different laboratories was very similar, but there was variability in the number of aberrations scored per aberrant cell. (3) The differences in the frequencies of aberrations between laboratories were minimal when the scoring was restricted to the first major peak of mitotic activity and sufficient cells were scored. It is concluded that using controlled experimentals conditions, human peripheral blood lymphocytes can effectively be used as a reliable biological dosimeter for absorbed radiation dose.

Argentina↗
PubMed1982

Differential sensitivity of muntjac lymphocyte chromosomes to mitomycin C, bromodeoxyuridine and hydroxylamine at different cell-cycle stages.

Quantitative and qualitative analyses were made of aberrations induced by 3 hitherto well-known mutagens, mitomycin C (MC), 5-bromodeoxyuridine (BUdR and hydroxylamine hydrochloride (HA), in muntjac chromosomes, during different stages of the cell cycle. The sensitivity to MC was increased in G1, reached its maximum in early S and was considerably decreased in late S and G2 stage treated cells. BUdR induced maximal aberrations when given during the synthetic phase and the cells in G1 and G2 were least affected. The sensitivity of the cells to HA in terms of induced chromosomal aberrations increased as they moved through the cell cycle, i.e. more damage was observed in cells treated in late S and G2 stage than in those treated at G1 and early S stages. While there were defined patterns of cell-cycle stage-dependent sensitivity for all 3 chemicals, the chromosomal sites being preferentially affected by each were found to be specific and invariant at different stages. Thus, it is presumed that the functional state of such "preferred sites" at one or other stage of the cell cycle is the factor responsible for the stage-dependent sensitivity of a cell towards these chemicals.

Animals↗
PubMed1981

Non-random distribution of aberrations and identification with C- and G-bandings of the position of breakage points on Muntjac chromosomes induced by mitomycin c, bromodeoxyuridine and hydroxylamine.

The analysis of chromosomes from muntjac after treatment of its lymphocyte cultures with 3 chemical mutagens having different base-pair affinities and modes of action, namely mitomycin C (MC), 5-bromodeoxyuridine (BUdR) and hydroxylamine hydrochloride (HA), with G- and C-band staining displayed non-random distribution of chemically specific damage points on them. The randomness of the involvement of each site on the chromosomes were examined by assuming an expected value calculated on the basis of its relative mitotic length. The observation revealed that a large fraction of MC-induced aberrations was preferentially located in the C-band positive constitutive heterochromatin, especially in the long "neck-like" centromeric region of the X-chromosome. On the chromosomal arms, the light G-bands were involved in aberrations either in proportion to or higher than that expected. When the cells were treated with BUdR, the dark G-bands on all the chromosomes of the complement were the preferred sites, displaying statistically significant higher numbers of aberrations. A single "hot-spot" for induced damage on 1 mid-q was also recorded. HA induced a very high frequency of damage in the secondary constriction regions of the chromosome pairs 1, X and Y2, and the frequency was slightly lower than this in the centromeres of 1, 2 and X chromosomes. The observation of specific distribution of damage points induced by the 3 chemicals lead to the suggestion that, though the effect of a chemical on chromosome segments depends on several factors, each being partially responsible for the end result, it is perhaps primarily depended by the chemical's base-pair affinity and mode of action.

Animals↗
PubMed1981

Culture media and species-related variations in the requirement of 5-bromodeoxyuridine for differential sister-chromatid staining.

Various concentrations of 5-bromodeoxyuridine (BdrU) ranging from 0.01 to 10.0 microgram/ml were tried for finding the minimal concentration required for differential staining of sister chromatids in lymphocytes of man, muntjac and cattle grown in three commonly used culture media, namely TC 199, Dulbecco's MEM and Ham's F-10. The lymphocytes grown in TC 199 required the lowest concentration of BrdU whereas it was highest for the lymphocytes grown in F-10. The minimal concentration varied for the 3 species studied, and it was not related to their DNA content. The differing amounts of thymidine and folic acid present in the various culture media seemed to account for the difference in the quantity of BdrU required for eliciting differential staining. Staining may also have depended on the intracellular nucleotide pool and/or on the difference in the substitutable dT sites of the genomes.

Animals↗
PubMed1980

Quantitative variation of "Mus musculus-like" constitutive heterochromatin and satellite DNA-sequences in the genus Mus.

The extent of conservation of constitutive heterochromatin in three species of Mus viz. M. musculus, M. booduga and M. dunni, with shared cytological properties and homologous DNA sequences has been studied. The cytological properties were investigated by doing fluorescence staining and condensation inhibition of their chromosomes with Hoechst 33258. Both the parameters indicate the occurrence of a reduced quantum of "M. musculus like heterochromatin" at specific sites in the other two genomes. In situ hybridization of the nick translated 3H-labelled M. musculus satellite DNA with M. booduga and M. dunni chromosomes, also corroborates our Hoechst 33258 findings and comparable variation in the amount and site of occurrence of sequences homologous to M. musculus satellite DNA in these species are noticed. The study thus provides a good example of a gradual quantitative variation of a particular type of heterochromatin and in turn of the repetitive DNA constituting it in different related species. Further since the heterochromatin in M. booduga and M. dunni is expected to contain different repetitive DNA sequences in addition to those homologous to M. musculus satellite DNA, it is proposed that a change in the balance between two or more repetitive sequences in heterochromatin may be more crucial in its evolutionary consequences rather than a mere increase or decrease of a homogeneous repetitive sequence.

Animals↗