Showing papers on "Nucleolar chromatin published in 1988"

Intranuclear differences in the response of Purkinje cell DNA of the rat cerebellum to bleomycin. A microphotometric and autoradiographic study.

Abstract: A single dose of the DNA-binding cytostatic agent bleomycin (100 micrograms/g body weight, subcutaneously) was given to 10-day-old rats to study unscheduled repair DNA synthesis in nucleolar and in bulk nuclear chromatin of postmitotic Purkinje neurons. The Feulgen reaction and Hoechst 33342 staining were used for quantitative evaluation of nuclear DNA content and chromatin structure. The repair synthesis of DNA was detected by 3H-thymidine autoradiography. The data showed a lesser staining of Purkinje as well as granule cell DNA by Hoechst 33342 in bleomycin-treated animals than in controls, but there was no difference in staining with the Feulgen reaction. The mechanisms of DNA staining by both cytochemical methods suggest that bleomycin reacted preferentially with AT-rich and single stranded DNA in cerebellar cells in vivo. Weak 3H-thymidine labelling was found in Purkinje cells of both control and treated rats, but in the latter group the labelling was more pronounced near or over the nucleolus. The enhanced unscheduled DNA synthesis in the nucleolar region of Purkinje cells of treated animals may be due to greater damage of DNA in this region or may indicate a greater ability of the nucleolar chromatin to repair its DNA.

Intercalary heterochromatin in the polytene chromosomes of Drosophila auraria.

Abstract: The distribution of intercalary heterochromatin in the salivary gland polytene chromosomes of Drosophila auraria is presented in this report, as revealed by the tendency of certain regions to pair ectopically, and by the existence of weak points. The two well-formed Balbiani rings, which are known to exist in this species, and the largest early ecdysone puff 73B, which corresponds to the puff 75B of D. melanogaster, seem to involve intercalary heterochromatin. Several pairings of nucleolar chromatin with certain chromosomal bands, as well as similarities in the intercalary heterochromatin distribution between D. auraria and D. melanogaster, are also presented.

Soft X-ray contact imaging of nucleolar chromatin using synchrotron radiation: a comparative scanning and transmission electron microscope study.

Abstract: SUMMARY Contact images (CI) of dehydrated, nucleolar chromatin from amphibian oocytes have been produced by soft X-rays from a synchrotron radiation source. These CI have been compared with the morphology of the original chromatin as seen in scanning and transmission electron microscopes. The quality and informational content of the CI depend very much on certain preparative procedures. The following factors have a marked effect on image quality and need to be carefully controlled: the total X-ray dose, the time and nature of development and the distance of the specimen from the photoresist. The preparation of the chromatin itself, providing that it is critically point dried, is less important. By following a regime of high X-ray dose, sufficient for penetration of the rather thick chromatin rings, and gentle development so that fine detail is not dissolved from the resist surface, it has been possible to obtain images which closely resemble the original chromatin, although the detailed resolution of the CI is not as clear. The smallest biological structures clearly resolved in the CI are ribonucleoprotein granules, which vary in size from 200 to 800 nm. However, by further refinement of preparative conditions it should be possible to improve on the informational content of these images.