Epigenetic Changes of Activity of the Ribosomal Cistrons of Human Acrocentric Chromatids in Fetuses, Middle-aged (22–45 years) and Old Individuals (80–106 years)

The level of total heterochromatin, Ag-positive nucleolar organiser regions (NORs) heterochromatin, non-associated and associated heterochromatin satellite stalks of acrocentric chromatids (some acrocentric chromosomal chromatid satellite stalks are connected to each other forming a satellite association), the intensity of each acrocentric chromatid involved in the association and types of associated chromatids were studied from 29 fetuses, from 32 healthy individuals 22–45 years (middle-aged) old and 22 healthy individuals 80–106 years old. The chromosomes were identified by the analysis of G-banding, using the Ikaros karyotyping system (Meta system). The differential scanning calorimeter showed an increase in chromatin thermostability (heterochromatinization) at adults (middle and old aged) compared with fetuses. The number of Ag-positive NORs per cell, for both associated and non-associated chromatids, was significantly increased in fetus cells than in middle and in extreme old age. The chromatid satellite association of fetus cells and the elderly was consistently reduced, compared with middle-aged individuals. Activity of chromatids of the 15th chromosomes, entered in association in the fetus, in middle and old age adults, was significantly reduced ( p < 0.05), compared to other acrocentric chromatids, while the chromatids of 21st chromosome participated in associations with high activity ( p < 0.05). The frequency of association of homologous (13:13; 14:14; 15:15; 22:22) and certain types of non-homologous chromatids (15:22 and 21:22) in the fetus and in 22–45 and 80–106 years old individuals was almost identically. The above noted phenomena apparently indicate that chromatid satellite ribosomal genes of acrocentric chromosomes undergo specific epigenetic variation depending on age, determining the specific synthesis of rRNA for constructing specific ribosomes, which may have great importance in assessing the general functioning of cells in normal and pathological conditions.