Electron microscopic examination of the sites of nuclear RNA synthesis during amphibian embryogenesis

Journal Article · Wed Sep 01 00:00:00 EDT 1965 · Journal of Cell Biology

DOI:https://doi.org/10.1083/jcb.26.3.937· OSTI ID:1629496

Karasaki, Shuichi ^[1]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biology Division; DOE/OSTI

The site of H³-uridine incorporation and the fate of labeled RNA during early embryo-genesis of the newt Triturus pyrrhogaster were studied with electron microscopic autoradiography. Isolated ectodermal and mesodermal tissues from the embryos were treated in H³-uridine for 3 hours and cultured in cold solution for various periods before fixation with OsO₄ and embedding in Epon. At the blastula stage, the only structural component of the nucleus seen in electron micrographs is a mass of chromatin fibrils. At the early gastrula stage, the primary nucleoli originate as small dense fibrous bodies within the chromatin material. These dense fibrous nucleoli enlarge during successive developmental stages by the acquisition of granular components 150 A in diameter, which form a layer around them. Simultaneously larger granules (300 to 500 A) appear in the chromatin, and they fill the interchromatin spaces by the tail bud stage. Autoradiographic examination has demonstrated that nuclear RNA synthesis takes place in both the nucleolus and the chromatin, with the former consistently showing more label per unit area than the latter. When changes in the distribution pattern of radioactivity were studied 3 to 24 hours after immersion in isotope at each developmental stage, the following results were obtained. Labeled RNA is first localized in the fibrous region of the nucleolus and in the peripheral region of chromatin material. After longer culture in non-radioactive medium, labeled materials also appear in the granular region of the nucleolus and in the interchromatin areas. Further incubation gives labeling in cytoplasm.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER). Biological Systems Science Division
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1629496
• Journal Information: Journal of Cell Biology, Journal Name: Journal of Cell Biology Journal Issue: 3 Vol. 26; ISSN 0021-9525
• Publisher: Rockefeller University Press
• Country of Publication: United States
• Language: English

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