spacer gif spacer gif spacer gif spacer gif spacer gif
QUICK SEARCH:   [advanced]


spacer gif
     Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents    

doi: 10.1242/jcs.00323

This Article
Right arrow Summary Freely available
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Wei, T.
Right arrow Articles by Zhonghe, Z.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Wei, T.
Right arrow Articles by Zhonghe, Z.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati   Add to Twitter  
What's this?

In situ visualization of rDNA arrangement and its relationship with subnucleolar structural regions in Allium sativum cell nucleolus

Tao Wei1,*, Huang Baiqu2, Liu Chunxiang1 and Zhai Zhonghe1,*

1 Department of Cell Biology, School of Life Sciences, Peking University, 100871, China
2 Institute of Genetics and Cytology, Northeast Normal University, Changchun, Jiling, 130024, China



View larger version (162K):

[in a new window]
  		Fig. 1. Ultrastructure of the Allium Sativum cell nucleolus and the morphological characteristics of DNA in the nucleolus after DNA-specific staining. (A) Conventional electron microscopic sample preparation. The nucleolus is composed of the fibrillar center (FC, arrows), the dense fibrillar component (DFC), the granular component (GC) and the nucleolar vacuoles (V). The nucleolus consists of many small FCs (arrows). In the FCs, dense chromatin clumps are distributed. (B,D) The DNA fibers appear in the nucleolar region after NAMA-Ur DNA-specific staining, and (C) the lowest electronic density region contains DNA clumps (arrows). D is an enlarged view of the nucleolus region of B. Bars, 0.5 µm.

 


View larger version (164K):

[in a new window]
  		Fig. 2. Immunolocalization of fibrillarin and specific DNA staining in nucleoli of Allium sativum cells. The gold particles are restricted to nucleoli. Gold particles are mainly distributed over the DNA fibers. Some gold particles are also present outside of the DNA fibers (arrows), but the regions with low electronic density (asterisks) are devoid of labeling. Nu, nucleolus Bar, 0.5 µm.

 


View larger version (176K):

[in a new window]
  		Fig. 3. In situ hybridization using an rDNA probe on sections processed with specific DNA staining. Gold particles are distributed over the DNA fibers. The arrow indicates a DNA clump within the FC (asterisks). Nu, nucleolus. Bar, 0.5 µm.

 


View larger version (118K):

[in a new window]
  		Fig. 4. The configuration of rDNA in the nucleolus after DNA-specific staining. The rDNA fibers are distributed around the FC, forming multiple circular rDNA arrangements (arrows). The DNA components within the FC remain in an aggregated states. Chr, chromatin DNA; Cyt, cytoplasm; Nu, nucleolus. Bar, 0.1 µm.

 


View larger version (165K):

[in a new window]
  		Fig. 5. Profile of the arrangement of rDNA in the nucleolus. (A) Although the FC contains large DNA clumps (arrows), FCs are still surrounded by decondensed rDNA; and the condensed DNA clumps within the FC are connected to rDNA fibers at the periphery of the FC. (B) Owing to different angles in sectioning, the periphery of some FCs (white arrows) is completely surrounded by rDNA, whereas in other FCs, the entire periphery is free of rDNA (black arrows). (C) After DNA staining, rDNA fibers were observed only at the DFC near the FC. The vacuoles of the nucleolus are mostly bleached, but their borders contain a few granular materials (white arrow). (D) rDNA is connected with the extranucleolar DNA at four sites (arrowheads). Bar, 0.5 µm.

 


View larger version (94K):

[in a new window]
  		Fig. 6. Micrographs of rDNA arrangement at high magnifications. (A,B) DNA clumps within FCs are connected with rDNA surrounding the FC by DNA fibers (white arrows). A and B are partial enlargements of C. Bar, 0.3 µm.

 


View larger version (163K):

[in a new window]
  		Fig. 7. rDNA ultrastructures after specific staining, showing the variation in thickness of rDNA fibers (A). Note the `arrow-like structures' along the thicker parts of the rDNA fiber (B,C,E). The maximum length of the arrow-like structures is 200 nm, whereas the fibers extending from these structures measure about 6 nm in diameter (E, arrows). D represents the transverse section of the arrow-like structure. Bar, 0.5 µm (A), 0.3 µm (B) and 30 nm (C-E). Asterisks indicate FCs.

 


View larger version (76K):

[in a new window]
  		Fig. 8. The distribution of Ag-NOR protein in the nucleolus. (A) Ag-NOR proteins are mainly distributed in the interior of the nucleolus and present as circular configurations with hollow centers. A is the enlarged image of the nucleolar region of B. (B) The complete picture of the cell nucleus after Ag-NOR staining. Ag-NOR proteins are mainly located in the nucleolus. N, nucleus; Nu, nucleolus; Cyt, cytoplasm. Bar, 0.3 µm.

 


View larger version (82K):

[in a new window]
  		Fig. 9. The similarity between rDNA and Ag-NOR arrangement configurations. A is one of the arrangements of rDNA. B is the circular distribution configuration of Ag-NOR protein. The magnification is the same for A and B. It can be seen that the arrangements of rDNA and Ag-NOR proteins are similar. Bar, 0.1 µm.

 


View larger version (53K):

[in a new window]
  		Fig. 11. Results from statistical analysis of the areas occupied by various nucleolar substructural regions, rDNA fibers, as well as the regions occupied by Ag-NOR proteins. The area of the region occupied by the extended rDNA fibers is approximately one-third of the total DFC; the area of the region occupied by Ag-NOR proteins is approximately the same as that occupied by rDNA fibers. (a) Total area of nucleolus; (b) granular components; (c) fibrillar center; (d) dense fibrillar component; (e) rDNA fibers; (f) Ag-NOR proteins.

 


View larger version (153K):

[in a new window]
  		Fig. 10. The nucleolus labeled with the RNA/DNA hybrid antibody. The signals of colloid gold particles for transcription sites are located at the periphery of FC and DFC regions near the FC (asterisks). Chr, chromatin; G, granular component. Bar, 0.5 µm.

 


View larger version (53K):

[in a new window]
  		Fig. 12. A model of the nucleolar ultrastructure of Allium sativum cells. rDNA is arranged in the DFC surrounding the FC, occupying about one-third of the total DFC, and the synthesis of rRNA is carried out in this region. The rDNA in the interior of the FC occurs in a condensed state and is possibly the anchoring site for the arrangement of rDNA and has no transcription activity. The distribution of rDNA is not uniform in the DFC. The splicing and processing of rRNA is carried in the other two-thirds of the DFC region, far away from FC and is transferred to the GC for the maturation processes of the ribosomal subunits. The white circles in the DFC represent splicing factors. FC, fibrillar center; DFC, Dense fibrillar component; GC, granular component; TChr, transcribing rRNA gene.

 

Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Reddit Reddit   Add to Technorati Technorati   Add to Twitter Twitter    What's this?



© The Company of Biologists Ltd 2003