DISCRIMINATION BETWEEN HOMOLOGOUS HUMAN INTERPHASE X-CHROMOSOME TERRITORIES
S. Yu. Demin,1 V. N. Stefanova 1, 2
1 Institute of Cytology, RAS, St. Petersburg, and 2 All-Russian Research Institute of Genetics
and Farm Animal Breeding, RAA,
St. Petersburg-Pushkin, Russia;
e-mail: vestefan@mail.ru
In accordance with molecular biology data reported elsewhere, homologous interphase X-chromosome territories differ greatly in the abundance
of inactive condensed chromatin. On the other hand, a three dimensional FISH (3D FISH) method has revealed that domains of both inactive and active X-chromosome
have similar volumes and similar maximum section areas (Smax)- To solve this contradiction, we examined differences between homologous
human interphase X-chromosome territories using two dimensional FISH (2D FISH) preparations of clustered PHA-stimulated lymphocytes. For obtaining such
preparations, we developed a new technique to avoid a stage of hypotonic treatment of living cells, since this treatment levels the chromatin compactness degree.
According to our 2D FISH data, the mean ratios of Smax for larger and smaller homologous X-chromosomes, calculated for individual flattened
nuclei, were 1.83 ± 0.08 and 2.02 ± 0.09, respectively, for clumped cells and groups of loosely associated and separated lymphocytes. In comparison, the same ratio
calculated for individual 3D nuclei of PHA-stimulated lymphocytes was 1.38 ± 0.05 (Falk et al., 2002). Our findings give evidence for enrichment of inactive
X-chromosomes by low stretchable condensed chromatin. In addition, these findings show that an active X is enriched by a high stretchable form of chromatin,
whose content may distinctly vary from cell to cell.
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