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Biomedical subjects

S R Rao

Publications and source records attributed to S R Rao.

At least 55 records · Page 3Linked to original sources
PubMed1988

Does heterochromatin variation potentiate speciation? A study in Nesokia.

An increasing incidence of sex-chromosome variation in constitutive heterochromatin, including individuals with mosaic genotypes, has been observed in a single natural population of Nesokia indica, the Indian mole rat. Variations in the heterochromatic areas of the X chromosome are largely due to deletions at R-band-positive regions corresponding to folate-sensitive fragile sites. All individuals with either a pre- or post-zygotic loss or gain of sex-chromosome heterochromatin have so far proved to be infertile. Whether such F1 sterility is due to abnormal gonadal development, gametic incompetence, or other factors is not clear. More important is the indication that the constitutive heterochromatin of this species may contain coding DNA sequences with putative regulatory functions.

Animals↗
PubMed1987

Folate-sensitive fragile sites on the X-chromosome heterochromatin of the Indian mole rat, Nesokia indica.

Folate-sensitive fragile sites have been demonstrated on the X chromosome of the Indian mole rat, Nesokia indica (subfamily Murinae), utilizing peripheral blood lymphocyte cultures. All normal female individuals expressed fragile sites on the constitutive heterochromatic long arm of one of their two X chromosomes (heterozygous expression); in contrast, no fragile sites were found on the single X chromosome of normal males. Preferential transmission of the maternal fragile X to the daughters is therefore suggested. Four sites have been detected so far: fra Xq1, fra Xq2, fra Xq3, and fra Xc (centromeric). It is significant that their location corresponds to the regions where constitutive heterochromatic deletions occur that result in a variety of polymorphic X chromosomes in natural populations of Nesokia. Thus there is a correlation between fragile sites, deletion sites, and karyotypic changes. In individuals that did not reproduce in the laboratory, there were more fragile sites on both X chromosomes of the females (homozygous/double heterozygous expression) and also on the X of the males (hemizygous expression). This difference in fragile site expression from the normal situation could be attributed to one or more new mutations. However, the mechanism by which fragile sites influence reproductive performance is unclear.

Animals↗
PubMed1986

Biliary ascariasis: ultrasonography, endoscopic retrograde cholangiopancreatography, and biliary drainage.

Roundworms migrating into the biliary tract are a relatively common cause of biliary symptoms in areas where the parasite is endemic. Visualization of worms by conventional radiologic methods is often unsatisfactory, whereas ultrasonography offers a rapid, safe, and noninvasive approach to the diagnosis. Using real-time ultrasonographic scanning we demonstrated for the first time the characteristic morphology of the worms in a patient with biliary ascariasis. In addition, the motility of the worms in the biliary tract could be confirmed. Ultrasonography is also a convenient method for the follow-up of patients. Endoscopic biliary drainage and instillation of piperazine citrate through a nasobiliary drain is a logical therapy and was used successfully in this patient.

Adult↗
PubMed1983

Insect sex chromosomes. VIII. Identification of active/inactive X-chromosomes in Gryllotalpa fossor by 5-BrdU/AO fluorescence.

By employing 5-BrdU/AO fluorescence technique to distinguish active from inactive X-chromosomes, we have, for the first time, provided evidence in support of the validity of this technique for a non-mammalian system Gryllotalpa fossor (Orthoptera). In the female somatic cells of Gryllotalpa, it is only in the active (euchromatic) arm of X-chromosome that the fluorescence is bright, whereas it is dull in the facultative and constitutive heterochromatic arms. In tetraploid spermatogonial cells one of the two X-chromosomes is inactive, suggesting that this phenomenon is probably a random one and that the inactivation process is independent of the imprinting mechanism.

Acridine Orange↗
PubMed1983

Heterochromatin variation and sex chromosome polymorphism in Nesokia indica: a population study.

Nesokia indica, the Indian mole rat, exhibits extensive variability (polymorphism) for the constitutive heterochromatin of the X and Y chromosomes. These polymorphic X and Y types range from a large metacentric chromosome to a small acrocentric one and occur in different frequencies in the population. On the assumption that there is random mating among individuals carrying these various X and Y chromosomes, the population shows Hardy-Weinberg proportions for the genotypes. However, notwithstanding the partial or total loss of constitutive heterochromatin of the X and Y chromosomes in a few individuals, its retention in most of the animals seems obligatory to the population at large. Hence, we suggest that the C-heterochromatin plays a "regulatory" role in the population dynamics of this species.

Animals↗
PubMed1982

Insect sex chromosomes. VI. A presumptive hyperactivation of the male X chromosome in Acheta domesticus (L.).

The functional status of the X chromosome in Acheta domesticus has been analysed at the whole chromosome level on the basis of (1) 3H-thymidine autoradiography, (2) 5-BrdU/AO fluorescence microscopy (3) in vivo 5-BrdU incorporation and (4) 3H-UdR induced aberrations. The rationale of these techniques in relation to the functional aspect of the X chromosome is that the inactive X chromosome would (1) show asynchrony in DNA synthesis, (2) show differential fluorescence, (3) respond differentially to in vivo 5-BrdU treatment and (4) the active X chromosome would show aberrations when treated with 3H-Uridine. From the results, it appears that the X chromosomes in both male (XO) and female (XX) somatic cells of Acheta are euchromatic (active). Further, the single X in the male is transcriptionally as active as the two X chromosomes in the female. In other words, the single X in the male is hyperactive when compared with the single X in the female. From this it is inferred that the male X chromosome is differentially regulated in order to bring about an equalization of it's gene product(s) to that produced by both Xs in the female. Drosophila melanogaster has a comparable system of dosage compensation. Thus, Acheta is yet another insect showing evidence for an X chromosome regulatory mechanism of dosage compensation. Additionally, it is surmised that sex determination in Acheta is based on an autosomes/X chromosome balance mechanism.

Animals↗
PubMed1982

In vivo sister chromatid exchanges in the euchromatin and constitutive heterochromatin of the Indian mole rat, Nesokia indica.

Distribution of in vivo SCEs in euchromatin and constitutive heterochromatin of Nesokia indica has been studied. The distinct partitioning of the euchromatin and constitutive heterochromatin into different arms of the large X chromosome greatly facilitates such a comparison. The constitutive heterochromatin showed a higher SCE rate per unit length than the total euchromatin. However, between the two types of chromatin in the X itself there was no significant difference. These values were also comparable to that observed for the largest autosome. This study suggests that factor(s) other than chromatin condensation, DNA base composition, and DNA replication kinetics is (are) responsible for the formation of SCEs.

Animals↗
PubMed1982

Radiation therapy in primary carcinoma of the vagina.

The experiences with irradiation of 25 patients with primary carcinoma of the vagina are presented. The 3-year survival was 36 per cent despite the fact that most of the cases were advanced. Further improvements in survival may probably be achieved with extension of the radium implantation to paravaginal tissues. Choice and technique of treatment must be individualized. Surgery is limited to the more advanced cases with involvement of the bladder and rectum.

Adult↗
PubMed1980

Renal failure in diabetes after intravenous urography.

A review of the literature reveals that patients with juvenile onset diabetes with azotemia, associated vascular disease, and proteinuria, are at great risk of sustaining acute renal failure following intravenous pyelography. Predisposing factors are identified, but the exact mechanism of acute renal failure remains obscure. Since no prophylactic measures or effective treatment exist, the benefits and risk must be weighed prior to the procedure.

Acute Kidney Injury↗
PubMed1979

Insect sex chromosomes. IV DNA replication in the chromosomes of Gryllotalpa fossor.

In Gryllotalpa the cell cycle duration in the hepatic caecae in vivo is about 12.5 h and of various phases are, G2 + P about 10 h, S about 2.5--3.5 h, and G1 appears negligible or absent. These estimates of the cell cycle are the only ones available in Gryllotalpidae. In the female Gryllotalpa, as in mammals, there is asynchronous DNA replication between the two euchromatic arms of the two X chromosomes. The other arm is constitutively heterochromatized and as expected is late replicating. Thus, a regulatory mechanism for dosage compensation by X chromosome inactivation appears to be operating in Gryllotalpa. This we believe, is the first cytogenetic demonstration of such a mechanism outside mammals.

Animals↗