Nucleolar organiser

Ayres JG, Crocker JG, Skilbeck NQ (1988) Differentiation of malignant from normal and reactive mesothelial cells by the argyrophil technique for nucleolar organiser region associated proteins. Thorax 43 366-370... 

Ag—AS staining AgNOs, followed by ammoniacal AgNOs and formalin Light Nucleolar organiser region rRNA synthesis... 

Some of the eady studies suggested that there were several nucleolar organiser regions (NORs), but the results obtained for most species using the AgNOj—AS method suggest that there are two... 

Since 1988, much of the B locus has been cloned and many of the subregions identified (Fig. 13.10h). Eventually, when each of the haplotypes can be distinguished by their gene sequence, the molecular genetic basis for their association with the biological traits may be clarified. The B locus has proved to be much more compact than the MHC loci in mice and humans. It is present on microchromosome 16 and is estimated to occupy at most 2000 kb the bulk of the microchromosome encodes the nucleolar organiser region (Fig. 13.10a) (Kroemer et al., 1990). The B-L... 

Biogenesis of ribosomes occurs in the nucleus where the rRNA genes are transcribed by RNA polymerase I to form 45S primary transcripts (Fig. 69.2). The first 45S primary transcript functions as a nucleolar organiser and induces the formation of a nucleolus where multiple copies of the ribosomal RNA genes are transcribed into rRNA. 

During the prophase the two most prominent events are the coiling and associated condensation of the chromosomes so that they become cytologically defined and the disappearance from the nucleolus (or nucleoli) of the RNA which is a prominent constituent of this structure during interphase. Often the nucleoli completely disappear as they become separated from the nucleolar organiser regions of the chromosomes during prophase condensation of the chromosomes. Then towards the end of prophase the nuclear envelope breaks down. 

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