Abstract
In maturing oocytes of the newt Triturus viridescens, the nucleoli undergo a series of morphological changes that are very similar to those described by Callan for the axolotl, Ambystoma mexicanum. The nucleoli first assume the form of spheroids which then become extended into ring or necklace shapes that are DNase-sensitive; in mature oocytes the nucleoli revert to a spheroidal form. Short term in vitro incorporation studies with uridine-3H on both species show that RNA synthesis occurs in a restricted, eccentric portion of the spheroidal nucleoli, thereby producing an asymmetrical pattern of labeling. In the ring forms, however, the localization of the radioactivity suggests that synthesis takes place symmetrically throughout their entire length. The changes in nucleolar morphology apparently reflect the fact that the component DNA has undergone a redistribution from a localized region in the spheroidal nucleoli to an extended circle in the rings; the patterns of uridine-3H incorporation, therefore, parallel the distribution of DNA in both the spheroidal and the ring nucleoli. Ultrastructurally, the nucleoli contain a fibrillar component that corresponds in position to that of the DNA. The typical spheroidal nucleolus consists of a fibrillar core situated eccentrically and surrounded by a hull of granular, ribonucleoprotein material. The ring nucleoli are composed of a central fibrous region that is ensheathed all around its circumference by a layer of similar granular material. This granular substance is thicker at intervals along the length of the rings, representing the "beads" of the necklaces.
Full Text
The Full Text of this article is available as a PDF (1.2 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- BROWN D. D., GURDON J. B. ABSENCE OF RIBOSOMAL RNA SYNTHESIS IN THE ANUCLEOLATE MUTANT OF XENOPUS LAEVIS. Proc Natl Acad Sci U S A. 1964 Jan;51:139–146. doi: 10.1073/pnas.51.1.139. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Callan H. G. Chromosomes and nucleoli of the axolotl, Ambystoma mexicanum. J Cell Sci. 1966 Mar;1(1):85–108. doi: 10.1242/jcs.1.1.85. [DOI] [PubMed] [Google Scholar]
- EDSTROEM J. E., GALL J. G. THE BASE COMPOSITION OF RIBONUCLEIC ACID IN LAMPBRUSH CHROMOSOMES, NUCLEOLI, NUCLEAR SAP, AND CYTOPLASM OF TRITURUS OOCYTES. J Cell Biol. 1963 Nov;19:279–284. doi: 10.1083/jcb.19.2.279. [DOI] [PMC free article] [PubMed] [Google Scholar]
- GALL J. G., CALLAN H. G. H3 uridine incorporation in lampbrush chromosomes. Proc Natl Acad Sci U S A. 1962 Apr 15;48:562–570. doi: 10.1073/pnas.48.4.562. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Gall J. G. Nuclear RNA of the salamander oocyte. Natl Cancer Inst Monogr. 1966 Dec;23:475–488. [PubMed] [Google Scholar]
- IZAWA M., ALLEFREY V. G., MIRSKY A. E. The relationship between RNA synthesis and loop structure in lampbrush chromosomes. Proc Natl Acad Sci U S A. 1963 Apr;49:544–551. doi: 10.1073/pnas.49.4.544. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Miller O. L., Jr Structure and composition of peripheral nucleoli of salamander oocytes. Natl Cancer Inst Monogr. 1966 Dec;23:53–66. [PubMed] [Google Scholar]
- Painter T. S., Taylor A. N. Nucleic Acid Storage in the Toad's Egg. Proc Natl Acad Sci U S A. 1942 Aug;28(8):311–317. doi: 10.1073/pnas.28.8.311. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Stevens B. J., Swift H. RNA transport from nucleus to cytoplasm in Chironomus salivary glands. J Cell Biol. 1966 Oct;31(1):55–77. doi: 10.1083/jcb.31.1.55. [DOI] [PMC free article] [PubMed] [Google Scholar]