Biomaterial Database

A re-evaluation of the relationships between the fibrillar centres and the nucleolus-organizing regions in reticulated nucleoli: ultrastructural organization, number and distribution of the fibrillar centres in the nucleolus of the mouse Sertoli cell. 1982

C Mirre, and B Knibiehler

In mouse testis, the diploid Sertoli cell displays one large nucleolus flanked symmetrically by two heterochromatic masses. The hybridization in situ with [3H]rRNA confirmed that the ribosomal cistrons are localized with in the central nucleolar mass. At the ultrastructural level this nucleolar mass appears to be reticulated and contains numerous fibrillar centres. These fibrillar centres are surrounded and interconnected by an electron-opaque fibrillar network, which constitutes the reticulated nucleolonema of the nucleolus. Ag--NOR staining reveals the presence of the argyrophilic proteins associated with active nucleolus-organizing regions (NORs) within both the fibrillar centres and the electron-opaque fibrillar component. Autoradiographic studies after [3H]uridine incorporation show that ribosomal DNA transcription only takes place in this dense fibrillar component. Three-dimensional reconstruction of four Sertoli cell nucleoli after serial sectioning reveals that the size and number of the fibrillar centers are very variable from one cell to another (26, 35, 38 an 41 fibrillar centres). The analysis of the volume occupied by the fibrillar centres as compared to the whole nucleolar volume demonstrates that the larger the nucleolus, the more fibrillar centres it contains, but also the more numerous the fibrillar centres, the larger their total volume. While in each case the number of the NORs is virtually the same, i.e. ten. In the light of these results we concluded that, at least in reticulated nucleoli, there is no numerical relationship between the number of fibrillar centres and the number of NORs, and that the fibrillar centers cannot be considered only as the nucleolar counterparts of the NORs. Moreover, the increasing number of fibrillar centres from the smallest nucleolus to the largest one is difficult to explain by the previously postulated hypothesis of a reserve of inactive rDNA packaged in the fibrillar centers. These data led us to reconsider the role of the fibrillar centres in the transcriptional activity of reticulated nucleoli.

UI	MeSH Term	Description	Entries
D008297	Male		Males
D008854	Microscopy, Electron	Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.	Electron Microscopy
D009693	Nucleic Acid Hybridization	Widely used technique which exploits the ability of complementary sequences in single-stranded DNAs or RNAs to pair with each other to form a double helix. Hybridization can take place between two complimentary DNA sequences, between a single-stranded DNA and a complementary RNA, or between two RNA sequences. The technique is used to detect and isolate specific sequences, measure homology, or define other characteristics of one or both strands. (Kendrew, Encyclopedia of Molecular Biology, 1994, p503)	Genomic Hybridization,Acid Hybridization, Nucleic,Acid Hybridizations, Nucleic,Genomic Hybridizations,Hybridization, Genomic,Hybridization, Nucleic Acid,Hybridizations, Genomic,Hybridizations, Nucleic Acid,Nucleic Acid Hybridizations
D009697	Nucleolus Organizer Region	The chromosome region which is active in nucleolus formation and which functions in the synthesis of ribosomal RNA.	Nucleolar Organizer,Nucleolar Organizers,Nucleolus Organizer Regions,Organizer Region, Nucleolus,Organizer Regions, Nucleolus,Organizer, Nucleolar,Organizers, Nucleolar,Region, Nucleolus Organizer,Regions, Nucleolus Organizer
D002466	Cell Nucleolus	Within most types of eukaryotic CELL NUCLEUS, a distinct region, not delimited by a membrane, in which some species of rRNA (RNA, RIBOSOMAL) are synthesized and assembled into ribonucleoprotein subunits of ribosomes. In the nucleolus rRNA is transcribed from a nucleolar organizer, i.e., a group of tandemly repeated chromosomal genes which encode rRNA and which are transcribed by RNA polymerase I. (Singleton & Sainsbury, Dictionary of Microbiology & Molecular Biology, 2d ed)	Plasmosome,Cell Nucleoli,Nucleoli, Cell,Nucleolus, Cell,Plasmosomes
D005796	Genes	A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms.	Cistron,Gene,Genetic Materials,Cistrons,Genetic Material,Material, Genetic,Materials, Genetic
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D012329	RNA, Bacterial	Ribonucleic acid in bacteria having regulatory and catalytic roles as well as involvement in protein synthesis.	Bacterial RNA
D012335	RNA, Ribosomal	The most abundant form of RNA. Together with proteins, it forms the ribosomes, playing a structural role and also a role in ribosomal binding of mRNA and tRNAs. Individual chains are conventionally designated by their sedimentation coefficients. In eukaryotes, four large chains exist, synthesized in the nucleolus and constituting about 50% of the ribosome. (Dorland, 28th ed)	Ribosomal RNA,15S RNA,RNA, 15S
D012708	Sertoli Cells	Supporting cells projecting inward from the basement membrane of SEMINIFEROUS TUBULES. They surround and nourish the developing male germ cells and secrete the ANDROGEN-BINDING PROTEIN and hormones such as ANTI-MULLERIAN HORMONE. The tight junctions of Sertoli cells with the SPERMATOGONIA and SPERMATOCYTES provide a BLOOD-TESTIS BARRIER.	Sertoli Cell,Cell, Sertoli,Cells, Sertoli