[Basic factors in the polyploidization of cerebellar Purkinfe cells in chick embryogenesis. III. Kinetics of RNA and DNA in Purkinje cell nuclei].

The content and concentration of RNA and DNA in the nuclei of the Purkinje cells of cerebellum of chick embryos (10-21 day-old) were determined by cytospectrophotometry. The RNA concentration shows a dayly rhythm, its content significantly increasing. The periods of the increase of RNA synthesis coincide with the periodicity of protein synthesis, the morphogenesis of the Purkinje cells and with the embryo's development as a whole. The DNA concentration remaining constant, its content increases sharply with the onset of the specific functional activity of cells and of the intensive growth of axons and dendrites. The variability of the mean values of this growth increases which is conditioned by the appearance of cells with hyperdiploid, tetraploid and hypertetraploid DNA contents in their nuclei. The Purkinje cells do not divide, their increased DNA content may be regarded as the expression of polyploidization or polytenization (which are functionaly equivalent) of a part of the nuclei. It is not excluded that in this case a differential gene amplification may take place. The increase of DNA content is associated with the onset of morphofunctional maturity of cells and may be due to a continuously increasing intensity of protein synthesis secured by the matrix material.