Ribosomal RNA genes (rDNA)

Ribosomal 18S-25S RNA Genes

Localization

The hybridization signals of the probe for the 18S-25S RNA genes were always located at the terminal position of the nucleolus-organizing regions (NOR) of the short arms of chromosome A and K and the long arm of chromosome I. The loci of the 18S-25S rDNA are situated in the segments Ap2, Iq3 und Kp2

Figure: Loci of the 18S-25S rDNA (yellow-green) on chromosomes A, I, and K. The scale bar represents 10 µm.

Figure: The 3 NO-chromosomes A,I, and K with loci of the 18S-25S rDNA probe. (a) DAPI, (b) Double filter for FITC and propidium iodide. Signals of the 18S-25S rDNA probe in yellow-green

Hybridization signal and condensation of rDNA

Figure: Different shape of hybridization signals of the 18S-25S rDNA (yellow-green) on two chromosomes K showing different degrees of condensation of the chromatin of the rDNA. (a) Large and distributed signal shape on decondensed chromatin . (b) Compact signal shape on condensed chromatin. The scale bar represents 10 µm. These fotos are taken from my diploma thesis (Nenno 1992).

Direct detection with FITC-dUTP

Figure: Loci of the 18S-25S rDNA (yellow-green) using directly with FITC-labeled (FITC-dUTP) probe. The scale bar represents 10 µm. This foto are taken from my diploma thesis (Nenno 1992).

Interphase and meiosis

In order to confirm the number of 3 chromosomes with 18S-25S rDNA loci also interphase nuclei and chromosomes in meiosis studied by FISH. As expected 6 FISH signals were observed on interphase nuclei and 3 signals on chromosomes in TelophaseII (haploid chromosome number).

Figure: Interphase nucleus showing 6 FISH signals (yellow/green). DNA is counterstained with propidium iodide(red).

Figure: Chromosomes in TelophaseII of Meiosis. (a) Chromosomes after DAPI staining. (b) Each of the four haploid chromosome sets show 3 FISH signals (yellow/green).

Genes of the ribosomal 5S RNA

The probe for 5S rDNA showed hybridization signals in the cHC of the NO-Chromosomes I and K. On Chromosome I the 5S rDNA locus is situated on the distal part of the cHC on the long arm in position Iq12. The second 5S rDNA locus was found on chromosome K at about the middle of the cHC of the long arm, the position of the weak DAPI band named Kq25. The co-localization with the 18S-25S and the 5S rDNA probe confirm that the loci of both rDNA types are found on chromosomes I and K.

Figure: Loci of the 5S (pink) und 18S-25S (green) rDNA on the chromosomes I and K. The scale bar represents 10 µm.