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Biomedical subjects

R Raman

Publications and source records attributed to R Raman.

At least 145 records · Page 8Linked to original sources
PubMed1987

Factors influencing replicon organization in tissues having different S-phase durations in the mole rat, Bandicota bengalensis.

In order to identify factors affecting the length of S-phase in mammals, DNA fibre autoradiograms from different tissues [bone marrow, phytohaemagglutinin (PHA)-stimulated spleen lymphocytes and whole body cells of new-borns] of the mole rat, Bandicota bengalensis, were examined for various parameters of replicon organization. The duration of S-phase in bone marrow and spleen was 12-14 h while that in new-borns was 8-9 h. Fork migration rate was significantly greater in new-borns than in bone marrow, and replicon size was significantly smaller in new-borns than in spleen. Thus it appears that several factors contribute, to varying degrees, in establishing the duration of S-phase in any cell type. In about 20% of the replicon clusters, constituent replicons were found to initiate replication asynchronously. This asynchronous initiation could possibly be due to an effect of transcription on time of initiation since it is likely that neighbouring replicons would be transcribed to different extents.

Animals↗
PubMed1987

Do sister forks of bidirectionally growing replicons proceed at unequal rates?

DNA fibre autoradiography in different tissues of the rodents Bandicota bengalensis and Nesokia indica reveals a high frequency of such bidirectionally replicating replicons whose sister 'hot' tracks are of unequal size. These results suggest intrarepliconic difference in the rates of fork migration in the two directions.

Animals↗
PubMed1987

Mammalian sex chromosomes. II. Pairing and alignment of the X and Y chromosomes of the pygmy mouse, Mus dunni.

In the pygmy mouse, Mus dunni, the entire Y chromosome and the short arm of the X and distal region of its long arm are constitutively heterochromatic. Different banding studies on somatic chromosomes revealed the GC nature of the distally located heterochromatin of the long arms of both the X and Y chromosomes. The short arm of the X and the rest of the Y are AT-rich. During meiosis, the long arms of the X and Y paired extensively, sometimes more than half of the Y pairing with the X. This observation is in disagreement with that of Pathak and Hsu (1976) who reported end-to-end pairing between the long arm of the X and the short arm of the Y. The orientation observed by us is favourable to a successful meiotic recombination but whether this takes place remains to be demonstrated.

Animals↗
PubMed1986

Mammalian sex chromosomes. I. Cytological changes in the chiasmatic sex chromosomes of the male musk shrew, Suncus murinus.

The X and Y chromosomes of the musk shrew are the two largest in the complement and they regularly form a single chiasma during meiosis. This chiasma is located in the short arms of the X and Y, both of which show partial C-banding at meiosis. The in vitro incorporation of 5-bromodeoxyuridine/tritiated thymidine during late S reveals that the non-C-band region of the Y finishes replication later than the C-band positive heterochromatin. During meiosis, the sex bivalent opens out early in pachytene to reveal a single chiasma which persists until late metaphase-I. In surface-spread, silver-stained meiocytes, the sex bivalent morphology changes from a phase of extensive pairing to one which includes a visible chiasma through a brief diffuse stage. Observations on C-banded meiocytes show a shift in the sex pair from a C-band positive to a negative state as compared to their corresponding somatic pattern. Comparable changes are also observed in the sex bivalents of other mammals which undergo a chiasmatic exchange. This suggests that in addition to pairing homology, an alteration in the chromatin configuration may be necessary for crossing over to occur between the sex chromosomes.

Animals↗
PubMed1983

Effects of Hoechst 33258 on different cell cycle events. I. Inhibition of synthetic activities in bone-marrow cells of the mole rat Bandicota bengalensis.

A study of the effects of the A-T base-specific ligand Hoechst 33258 on the cell cycle events of the bone-marrow cells of the mole rat Bandicota bengalensis reveals that (1) the G2 phase is prolonged by 2 h; (2) the chromosomes are undercondensed to varying degrees in about 30% metaphases; (3) DNA as well as RNA synthesis is partially inhibited. Study on DNA fibre autoradiograms shows that despite the inhibition of DNA synthesis the average replicon size and rate of fork migration remain unchanged, but there is a marked asynchrony of initiation of replicons in replicon clusters in H-treated cells in comparison with control. It is suggested that these inhibitory effects result from the stabilization of the double-stranded organization of DNA (dsDNA) by the drug so that the unwinding of DNA at the replication or transcription origin sites is greatly impaired. It is likely that this introduces asynchrony in the initiation of replicons within replicon clusters which may retard the overall rate of replication. In addition, it appears that the reduction in transcription is at least one cause for the prolongation of G2 phase.

Animals↗
PubMed1983

A simple method of staining the synaptonemal complex with Coomassie brilliant blue for light microscopy.

A simple technique for staining synaptonemal complexes with Coomassie brilliant blue for light microscopy has been described. The testis cells were exposed to prolonged hypotonic treatment and dropped on Formvar-coated slides. Following fixation with paraformaldehyde the slides were stained with Coomassie brilliant blue for 15 min to 1 h at room temperature and rinsed in distilled water. For its simplicity and rapidity this technique may serve as an effective alternative to silver staining for light microscopic observation of synaptonemal complexes.

Animals↗