The number of silver-staining NORs (rDNA) in lymphocytes of newborns and its relationship to human development.

The number of silver-staining NORs (rDNA)/cell and their pattern of distribution were studied in phytohaemagglutinin-stimulated blood lymphocyte chromosomes of different age group individuals starting from newborns to old age (0-75 years) in order to investigate if the number of Ag-NORs or rDNA genes varies during development in humans. The results indicate presence of a relatively high modal number of NORs in newborns and infants (9.00 and 8.00/cell, respectively) and a significantly reduced number in old individuals (6.00/cell) as compared to that of normal adults (7.00/cell). These data are complimentary as well as comparable to the previous findings of Denton et al. (Mech. Ageing Dev., 15 (1981) (1-7). It is suggested that at young age due to an obvious enhanced growth and differentiation more gene sites may be transcriptionally active showing higher number of silver-stained NORs but as the development proceeds and the age advances many of these may be gradually repressed or inactivated.