On the relationship between the perichromatin granules and cellular ageing as well as cell differentiation.

Current hypotheses ascribe the role of pre-RNA storage or transport structures to the perichromatin granules. Their numerical density is directly related to the transcription activity of the nucleus. The perichromatin granules (P.K.) can be demonstrated in ultrathin sections with the stain used by Bernhard (1969) for ribonucleo-proteins. We have established the numerical density per unit of area in nuclear cross-sections of cells in young rats (1-2 months), old rats (26-29 months) and in relation to various cell function types. Cell aging causes a reduction in the numerical density of perichomatin granules in the big neurons of the cerebral cortex, the cerebellar granulocytes, the hepatocytes and the parotid cells. No age-related changes were found in the myocardial cells and erythroblasts of the same maturity. However, at the end of maturation, the number of perichromatin granules both in young and old erythroblasts was nil. (1) There is a quantitative reduction of perichromatin granules primarily in postmitotic and relatively postmitotic cells; (2) cell types showing no age-related reduction in perichromatin granules maintain high synthetic activity throughout their life; (3) the results confirm that relationships exist between numerical density of the perichromatin granules and cell activity; (4) the big fluctuations in the numbers of perichromatin granules in various cell types are probably connected with cell function.