NORs and statellite associations in a family with 13/14 translocation

Nucleolus organizing region (NOR) activity in seven probands with Down syndrome due to a de novo (21 ;21) trans-location and their parents was analyzed on the basis of total Ag-NOR size per cell, mean Ag-NOR size per cell (X_c), mean Ag-NOR size per acrocentic (X_a), 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 (GX_c) and the mean Ag-NOR size per acrocentric for each group (GXJ were calculated, a number of interesting and significant correlations were found: (1) GX_c correlated perfectly with the group’s characteristic Ag-NOR number, (2) GX_a varied inversely with the group’s characteristic Ag-NOR number, and (3) GX_c and GX_a 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.

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“…Jotterand-Bellomo and van Melle ( 1981). Nikolis et al (1981), andZakharov et al (1982). Intercellular variations are illustrated in Fig.…”

Section: Resultsmentioning

confidence: 99%

Evidence for a compensatory mechanism regulating Ag-NOR activity in families with de novo 21;21 translocation Down syndrome

Nikoliš

Kekić²

1988

Cytogenet Genome Res

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Reduced NOR association frequency in a 13/18 translocation chromosome. A family study

1983

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The association frequency of a functional, intercalary NOR in fibroblasts of five carriers of a translocation t(13;18) was significantly lower than the average association frequency of normal G- and D-group chromosomes in the same carriers. This decreased coefficient of association does not seem to be attributable to partial loss of the NOR during rearrangement or to a loss of NOR activity, as indicated by silver staining. It is hypothesized that either (1) interphase associations including this chromosome form less frequently or, more likely, (2) associations with this chromosome are differentially susceptible to physical disruption due to flattening of association complexes during cell preparation. The presence of this abnormal NOR chromosome did not affect the association behavior of normal G- and D-group chromosomes in carrier cells. In addition, the present study supports previous observations that G-group chromosomes associate with a greater average frequency than D-group chromosomes.

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De novo 21/21 translocation Down syndrome

Nikoliš

Kekić

1986

Hum Genet

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Among ten families with de novo 21/21 translocation Down syndrome (tDS), four were informative, according to the studies of structural variants of chromosome 21, about the origin of the aberrant chromosome. In three of these, the translocation originated in the paternal and in one in the maternal gametogenesis. The parents with meiotic failure were compared with 20 control individuals (10 males and 10 females). There were no significant differences between them in the association coefficient of chromosome 21 and in the frequency of 21-21 associations. Similar results were obtained previously with the entire sample of tDS parents. The results obtained, unless they reflect too small a sample, suggest that the origin of the aberrant chromosome is not related to an increased chromosome 21 association tendency. It could be supposed that in the case of an apparent 21/21 translocation, the 21q isochromosome, morphologically indistinguishable from the Robertsonian translocation, is in question. The Ag-NOR negative acrocentrics in the tDS parents reappeared in the probands confirming the heritability of that nucleolus organizer regions (NOR) trait.

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NORs and statellite associations in a family with 13/14 translocation

Cited by 4 publications

References 23 publications

Evidence for a compensatory mechanism regulating Ag-NOR activity in families with de novo 21;21 translocation Down syndrome

Evidence for a compensatory mechanism regulating Ag-NOR activity in families with de novo 21;21 translocation Down syndrome

Reduced NOR association frequency in a 13/18 translocation chromosome. A family study

De novo 21/21 translocation Down syndrome

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