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Biomedical subjects

R Simard

Publications and source records attributed to R Simard.

At least 55 records · Page 3Linked to original sources
PubMed1972

Detection of DNA by tritiated actinomycin D on ultrathin frozen sections.

Ultrathin frozen sections of fresh liver tissue were floated on actinomycin D-(3)H. Quantitative high resolution radioautography was performed to determine the value of the method for detection of DNA by electron microscopy. A complete series of control experiments involving various treatments of frozen sections with enzymes (pronase, DNase) and 0.1 N HCl were also carried out to determine the specificity of the labeling. The results indicate the value of the method for detection of DNA directly on ultrathin frozen sections. Short treatments with pronase followed by DNase reduce the labeling to zero, whereas removal of chromosomal proteins with HCl increases the amount of radioactivity in the nucleus considerably. The results are discussed in view of the future applications opened by ultracryotomy, since radioautographic detection of various macromolecules and cellular components by labeled compound with specific affinities will now be possible.

Animals↗
PubMed1967

A heat-sensitive cellular function located in the nucleolus.

Striking nucleolar lesions occur in cultured cells after exposure to supranormal temperatures. These lesions appear at 42 degrees C and consist of a loss of the granular ribonucleoprotein (RNP) component and intranucleolar chromatin, and a disappearance of the nucleolar reticulum. The material remaining in the morphologically homogeneous nucleolus is a large amount of closely packed fibrillar RNP. The lesions remain identical as temperature increases to 45 degrees C. These alterations are reversible when the cells are returned to 37 degrees C and are associated with the reappearance of an exaggerated amount of intranucleolar chromatin and granular RNP. High-resolution radioautography indicates that after thermic shock nucleolar RNA synthesis is inhibited whereas extranucleolar sites are preserved: it also suggests that the granular RNP is reconverted to fibrillar RNP probably by simple unraveling. The results prove the existence of heat-sensitive cellular functions in the nucleolus which deal with the DNA-dependent RNA synthesis. The precise site of action is assumed to involve hydrogen bonds, resulting in configurational changes in nucleolar RNP and affecting the stability of the DNA molecule. The subsequent events in nucleolar RNA synthesis are discussed in light of the morphologic and biochemical effects of actinomycin D on the nucleolus.

Animals↗