[DNA synthesis in the Purkinje cell nuclei of the chick embryo cerebellum in the process of their differentiation and morphofunctional specialization].

Single injections of 3H-thymidine was introduced into chick embryos on days 10, 13 and 15 of development. The label incorporation into the cell nuclei was determined on days 13--20, i. e. during differention and specialization of the Purkinje cells, with the complete absence of their proliferative activity. 3H-thymidine was incorporated in 5.2--38.5% cases. The labeling index and labeling intensity increased with ageing, which is in direct correlation with the increase of DNA content in the nuclei, and with the number of cells having increased DNA contents. It is concluded that the synthesis observed is not a premitotic or reparative one, and that it is closely related to the process of cell defferentiation and specialization. On the basis of our and literature data, the question of non-proliferative replicative DNA synthesis (DNA hyperreplication) in the nuclei of neuronal cells, and especially in the Purkinje neurons, is discussed. In the authors' opinion, this phenomenon is necessary condition for the realization of differentiation and specialization processes in the cell population of developing organisms.