Vergleich der Aktivität Nucleolus organisierender Regionen an Metaphasechromosomen embryonaler Gewebe und Fibroblastenkulturen der Wachtel (Coturnix coturnix japonica)

The silver labelling technique by HOWELL and BLACK (1980) was used to stain active chromosomal nucleolus organizer regions (NOR) of embryonic tissues and fibroblast cultures in Japanese quail. Active rRNA gene clusters were localised always at very small microchromosomes, which were not distinguishable in their common morphology. A minimum of 2 and a maximum of 8 NORs were observed, however, over 94% of all spreads had 4 up to 6 active nucleolus organizer regions. Tissues of 2-d-old embryos embody with 5.12 (± 0.27) slightly more NORs that 4-d-old embryonic tissues (5.01 ± .26). No significant differences between these embryonic stages were calculated within all populations of Japanese quail (P > 0.05). Also, no difference in the mean number of active NORs between embryonic stages (5.07 ± 0.26) and fibroblast cultures of adult individuals (5.09 ± 0.20) was determined (P > 0.05). A significant decrease in the mitotic index from 2- to 4-d-old embryos was of no effect on the number and variation of active chromosomal nucleolus organizer regions. Earlier experiments at the same material showed a similar decrease of mitotic rate and expression of rRNA genes investigated in different parameters of nucleoli in interphase cells (WAGNER et al., 1994). Therefore, the present results indicate that, the regulation of gene expression is rather caused by each single rRNA Loci of all NORs than by "turn on" or "turn off" of an entire nucleolus organizer region.