The relationship between DNA synthesis and nuclear proteins in the cerebrum and cerebellum of 8-day-old rats

Morphological identification and biochemical characterization of isolated brain cell nuclei from the developing rat cerebellum

Cell nuclei from developing rat cerebellum were isolated and the various types of nuclei were characterized and quantified. Nuclear pellets appeared to be both quantitatively and qualitatively representative of the entire cerebellum, and of sufficient purity to perform biochemical studies as well as morphological comparison with histological sections. Isolated nuclei were classified into 6 groups based on nuclear size and shape, heterochromatin aggregations, and nucleoplasmic density. The total population of cerebellar cells primarily consisted of two types of nuclei after day 10. One group of nuclei, resembling those of internal granule neurons or external germinal cells, contributed at least 70% of the total isolated cell nuclei from day 1 to day 90, whereas another nuclear group that was identified as dark oligodendrocytes constituted 8-9% of the total population on days 45 and 90. Nuclear DNA, RNA, and protein content of the cerebellum also were determined throughout postnatal development. DNA concentration markedly declined after day 15, while the RNA/DNA ratio increased until day 3 and remained constant to day 90. The nuclear protein/DNA ratio increased from birth to day 3, decreased to its lowest value on day 10, and increased to day 90. Utilizing DNA values, the total cell population as well as contributions of different cell types were calculated. At birth the cerebellum was estimated to contain 5.9 million cells, increasing to 94 million by day 21. By day 90, 107 million cells were present, of which 8.6 million oligodendrocytes and 93.6 million internal granule cells were estimated.

Changes of CTP synthetase activity during postnatal rat brain development

The activity of CTP synthetase (UTP: ammonia ligase (ADP, EC. 6.3.4.2.) was determined in rat cerebral hemispheres and cerebellum during postnatal development. It was found that enzyme activity, when expressed per unit of protein or wet tissue weight, in both parts of the brain decreased with age, the diminution proceeding more rapidly in the cerebellum than in the hemispheres. When CTP synthetase was expressed on the basis of DNA an activity peak in the hemispheres with a maximum on the 5th day after birth was observed. The enzyme content per cell was several times lower in the cerebellum than in the hemispheres at each age studied, with the exception of 1-day-old animals, in which both tissues displayed similar activity. The results obtained were compared with literature data for the intensity of RNA synthesis in the developing brain. The conclusion was reached that the changes of CTP synthetase activity were closely related to the RNA metabolism. Therefore the enzyme under study may be one of the factors involved in cell control of RNA synthesis.