|
|
|
|
|
|
|
|
|||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | |||||
Journal of Cell Science, Vol 10, 339-367, Copyright © 1972 by Company of Biologists
Submitted on July 21, 1971
1 Laboratoire de Cytologie et Embryologie moleculaires, Université Libre de Bruxelles, 67 Rue des Chevaux, 1640 Rhode St Genèse, Belgium
Xenopus laevis tadpoles and toads were killed at several ages. The structure of the nuclei of the germinal cells has been observed by light and electron microscopes. We distinguish 11 successive stages in nucleolar structure: (1) a single, essentially granular nucleolus in the oogonium (10 µm diameter), (2) a reticulated nucleolus in the leptotene oocyte, (3) fragmentation of this nucleolus into a few smaller nucleoli, (4) multiple tiny nucleoli appearing in the cap of the pachytene oocyte, (5) enrichment in the fibrillar constituent of these intra-cap nucleoli, (6) grouped spherical nucleoli, with well segregated granular and fibrillar constituents, as the disintegration of the cap is going on (diplotene A oocyte, 30 µm diameter), (7) dispersion of those nucleoli in the nuclear sap (diplotene B oocyte, 50 µm diameter), (8) formation of long, ribboned nucleoli with multiple DNA-rich spots (diplotene C oocyte, 100 µm diameter), (9) fragmentation of the nucleolar ribbons into multiple spherical nucleoli with excentric fibrillar core and granular cortex (diplotene D oocyte, 150 µm diameter), (10) multiple purely fibrillar nucleoli (diplotene E oocyte, between 150 and 400 µm diameter), and (11) multiple classical nucleoli with concentric fibrillar core and granular cortex (diplotene F oocyte, between 400 and 1000 µm diameter).
The multiplication of the nucleoli in Xenopus laevis may occur successively (a) by the fragmentation of the single oogonium nucleolus at the leptotene stage, (b) by de novo formation of nucleolar bodies inside the cap at the pachytene stage, and (c) by the growth of those nucleoli lying free in the nucleolar sap at the early diplotene stage. They evolve into nucleolar ribbons which later on fragment into spherical bodies.
Four successive phases during the growth of an oocyte can be distinguished with respect to the ribosomal system. (I) The first phase is characterized by the nucleolar DNA amplification. (II) During the second phase, the multiplication of the nucleoli is going on. Ribosomes are present in the cytoplasm and the rate of cellular growth is very high. (III) During the third phase, the synthesis of rRNAs seem to be repressed while the synthesis of heterogenous small RNAs is going on. Ribosomes are no longer visible in the cytoplasm. The nucleoli are purely fibrillar. The rate of cell growth is lower than in the preceding phase. (IV) During the fourth ( = Duryee lampbrush stages 3-6), or vitellogenic phase, rRNAs are actively synthesized and numerous ribosomes appear in the cytoplasm. The nucleoli have the classical structure and the rate of growth is about the same as during phase III.
Submitted on July 21, 1971
This article has been cited by other articles:
|
|
 |
|
  A. O. Manfiolli, A. L. G.C. Maragno, M. M.A. Baqui, S. Yokoo, F. R. Teixeira, E. B. Oliveira, and M. D. Gomes FBXO25-associated Nuclear Domains: A Novel Subnuclear Structure Mol. Biol. Cell, May 1, 2008; 19(5): 1848 - 1861. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Shav-Tal, J. Blechman, X. Darzacq, C. Montagna, B. T. Dye, J. G. Patton, R. H. Singer, and D. Zipori Dynamic Sorting of Nuclear Components into Distinct Nucleolar Caps during Transcriptional Inhibition Mol. Biol. Cell, May 1, 2005; 16(5): 2395 - 2413. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C Mais and U Scheer Molecular architecture of the amplified nucleoli of Xenopus oocytes J. Cell Sci., January 2, 2001; 114(4): 709 - 718. [Abstract] [PDF]
|
|
