Nucleolus organizer

Rilschoff, J., Plate, K. H., Contractor, H., Kem, S., Zimmermann, R., and Thomas, C. 1990. Evaluation of nucleolus organizer regions (AgNORs) by automatic image analysis a contribution to the standardization. J. Pathol. 767 113-118. 

De Capoa A, Ferraro M, Lavia P, Pelliccia F, Finazzi-Agro A (1982) Silver staining of the nucleolus organizer regions (NOR) requires clusters of sulfhydryl groups. J Histochem Cytochem 30 908-11... 

Howell, W. M and Black, D. A. (1980). Controlled silver staining of nucleolus organizer regions with a protective colloidal developer A I step method. Experientia 36, 1014-1015. 

Kodama, Y.. Yoshida, M. C., and Sasaki, M. (1980). An improved silver staining technique for nucleolus organizer regions by using nylon cloth. Jpn. J. Hum. Genet. 25, 229-233. 

Chan, E. K. L., Imai, H., Hamel, J. C., and Tan, E. M. (1991). Human autoantibody to RNA polymerase 1 transcription factor hUBF. Molecular identity of nucleolus organizer region autoantigen NOR-90 and ribosomal RNA upstream binding factor. J. Exp. Med. 173, 1239-1244. 

Howell, W. M. (1982). Selective staining of nucleolus organizer regions (NORs). In The Cell Nucleus (H. Busch and L. Rothblum, eds.), Vol. 11, Part B, pp. 89-142. Academic Press, New York and London. 

Ohno, S., W. D. Kaplan, and R. Kinosita. 1957. Heterochromatic regions and nucleolus organizers in chromosomes of the mouse,musculus, Exp. Cell Res., 13 358-364. 

However, Spear and Gall (1973) questioned whether somatic magnification does occur in Drosophila. rRNA—DNA saturation hybridization experiments with DNA isolated from diploid tissues revealed that XX flies contain about twice as much rDNA than XO flies. Thus, in diploid cells, the rRNA genes are present in amounts proportional to the number of nucleolus organizers. In contrast to the situation in diploid cells, polytene chromosomes of the salivary glands from XX and XO flies, respectively, contain the same amount of rDNA. Since it is known that adult Drosophila flies do contain polytene chromosomes, the rDNA increase in XO flies reported by Tartof (1971, 1973) could result from the relatively higher amount of rDNA present in polytene chromosomes... 

Nucleolus organizer a specific region on one or more eukaryotic chromosomes, where the nucleolus is formed. The DNA in this region contains genetic information for the synthesis of ribosomal RNA. 

Long ago the suggestion was made that excess of DNA in Bufo oocytes could be explained by the formation of extra copies of the nucleolus organizer (Painter and Taylor, 1942). This hypothesis was further developed by Lima-de-Faria (Lima-de-Faria and Mozes, 1966 Lima-de-Faria et al., 1969). 

The extra copies are replicates of one (or more) of several hundred repeated sequences of rDNA of the nucleolus organizer. This is a mechanism of chromosomal amplification. 

In this case it is not important how successive copies are synthesized, from the original or from the replicate chromosomal rDNA of the nucleolus organizer. 

Interesting results were observed in experiments with rRNA synthesis in Xeno-pus laevis with mutations p and p These mutations caused an insufficiency of the nucleolus organizer (NO) and are similar in their expression to bobbed mutation in Drosophila. It was found that these mutants synthesized rRNA at a rate... 

Matsui S. and Sasaki M. 1973. Differential staining of nucleolus organizers in mammalian chromosomes. Nature 246 148-150. 

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