Biomaterial Database

Quantitative determination of amplified rDNA and its distribution during oogenesis in Xenopus laevis. 1979

C H Thiébaud

The number of extra-chromosomal nucleoli and their rDNA content were determined during oogenesis in Xenopus laevis. The highly variable number of nucleoli (500 to 2,500) in oocytes of the same stage and from the same female or of different stages or from different females is not a measure of the extent of amplification. In all oocytes examined, a inversely proportional relation was found between the number of nucleoli in an oocyte and their mean rDNA content. These results indicate that there is no variation of the rDNA content of oocytes during oogenesis nor between oocytes of different females. The varying nucleolar numbers found in oocytes result thus from fusion and fission of pre-existing nucleoli. The determination of the rDNA content, in absolute units (35 pg), after amplification which occurs at the beginning of oogenesis, makes it possible to calculate the rDNA content of one nucleolus. This ranged from 0.7.10(-2) pg to 15.10(-2) pg, corresponding to about 500--11,000 cistrons of rDNA. No distinct size classes between these two extremes were observed.

UI	MeSH Term	Description	Entries
D009866	Oogenesis	The process of germ cell development in the female from the primordial germ cells through OOGONIA to the mature haploid ova (OVUM).	Oogeneses
D010053	Ovary	The reproductive organ (GONADS) in female animals. In vertebrates, the ovary contains two functional parts: the OVARIAN FOLLICLE for the production of female germ cells (OOGENESIS); and the endocrine cells (GRANULOSA CELLS; THECA CELLS; and LUTEAL CELLS) for the production of ESTROGENS and PROGESTERONE.	Ovaries
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
D004247	DNA	A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine).	DNA, Double-Stranded,Deoxyribonucleic Acid,ds-DNA,DNA, Double Stranded,Double-Stranded DNA,ds DNA
D004261	DNA Replication	The process by which a DNA molecule is duplicated.	Autonomous Replication,Replication, Autonomous,Autonomous Replications,DNA Replications,Replication, DNA,Replications, Autonomous,Replications, DNA
D005260	Female		Females
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
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
D014981	Xenopus	An aquatic genus of the family, Pipidae, occurring in Africa and distinguished by having black horny claws on three inner hind toes.