Evidence for a compensatory mechanism regulating Ag-NOR activity in families with de novo 21;21 translocation Down syndrome.
Nucleolus organizing region (NOR) activity in seven probands with Down syndrome due to a de novo (21;21) translocation and their parents was analyzed on the basis of total Ag-NOR size per cell, mean Ag-NOR size per cell (Xc), mean Ag-NOR size per acrocentic (Xa), and the characteristic Ag-NOR number of each subject. The results showed intercellular variations in total Ag-NOR size per cell in all subjects, as well as interindividual variations in mean Ag-NOR size per cell. When the subjects were grouped according to their characteristic Ag-NOR number and the mean Ag-NOR size per cell for each group (GXc) and the mean Ag-NOR size per acrocentric for each group (GXa) were calculated, a number of interesting and significant correlations were found: (1) GXc correlated perfectly with the group's characteristic Ag-NOR number, (2) GXa varied inversely with the group's characteristic Ag-NOR number, and (3) GXc and GXa varied inversely with each other. These results suggest that if the Ag-NOR number of a cell decreases, the total NOR activity of the cell also decreases, but the NOR activity of its chromosomes increases. This finding supports the existence of a compensatory mechanism that regulates NOR activity on the cellular level.
Nikolis
J
J
Institute of Biology and Human Genetics, Faculty of Medicine, University of Belgrade , Yugoslavia.
Kekic
V
V
D002891:Chromosomes, Human, Pair 21; D004314:Down Syndrome / Q000235:genetics*; D005260:Female; D006801:Humans; D007621:Karyotyping; D008297:Male; D009697:Nucleolus Organizer Region / Q000502:physiology*; D010290:Parents; D012834:Silver; D013194:Staining and Labeling; D014178:Translocation, Genetic
D012834:Silver