Mitosis and Deoxyribonucleic Acid Content of the Nucleus

Abstract

ALTHOUGH a certain number of exceptions have been revealed in tissues which show increased mitotic or physiological activity^1–3, it has been shown that as a rule the deoxyribonucleic acid content of the interphasic nuclei of tissues of a given species corresponds to a constant equilibrium value, which is double that of the deoxyribonucleic acid content of the spermatic nuclei of the same species. Consequently, at each mitotic division, synthesis of deoxyribonucleic acid must take place in order that the quantity of this substance should be restored in the nuclei of the daughter cells at a ‘normal’ level. Histophotometric measurements have shown that, contrary to classic opinion, this synthesis takes place in the interkinetic phase and not during mitosis. According to some authors, this occurs immediately before mitosis^4–7, so that the content reaches double that of the normal value: after division each nucleus of the daughter cells receives also a normal content. According to other authors^1,8–11, synthesis occurs soon after mitotic division when nuclei of the daughter cells which receive only half of the normal content restore the latter.