THE RELATIONSHIP BETWEEN DNA SYNTHESIS AND THE SYNTHESIS OF NUCLEAR PROTEINS IN RAT BRAIN DURING DEVELOPMENT¹

Abstract

—The incorporation of [3H]thymidine into nuclear DNA of rat brain progressively increased from birth until the 8th postnatal day and it was lowest in the adult brain. When isolated nuclei from brain cells were separated into a neuronal‐ and a glial‐rich fraction (composed of glial and neuroblast nuclei in young animals), the specific radioactivity of the DNA was higher in the glial‐rich fraction at all ages investigated. The incorporation of [3H]leucine into proteins of rat brain was considerably higher in the 8‐than in the 1‐day‐old rat. The greatest difference in the rate of protein synthesis between 8‐ and 1‐day‐old brain occurred in the nuclear proteins, especially those associated with DNA. There was an accumulation of protein and RNA in nuclei from brain cells from birth to the 8th postnatal day. The increased content of proteins occurred primarily in the fraction soluble in buffered saline (nuclear sap).

Purification of plasma membranes from immature brain

“…Although the exact number of spongioblasts in immature rat brain has not been established, histological follow-up studies [ 17] and data on cell multiplication [18] indicate that the cells are predominantly developing neurons, which are forming their connections to other neurons. The presented procedure, which for the first time describes isolation of plasma membranes from immature solid brain tissue, may be applied in studies of the plastic membrane changes occuring during the development of the brain.…”

“…Immature rat cortex is suitable material for the isolation of neuronal enriched plasma membranes, because the tissue contains few glial cells and little myelin [14,17,18]. Although the exact number of spongioblasts in immature rat brain has not been established, histological follow-up studies [ 17] and data on cell multiplication [18] indicate that the cells are predominantly developing neurons, which are forming their connections to other neurons.…”

NUCLEAR PROTEIN PATTERNS IN DEVELOPING AND ADULT BRAIN AND IN ETHYLNITROSOUREA‐INDUCED NEUROECTODERMAL TUMOURS OF THE RAT1,2

“…OLPE et al (1972), in a comparative analysis of the respective NHP banding patterns of 5-, 10-and 20day-old, as well as adult rat brain chromatin, isolated and separated on polyacrylamide gels containing sodium dodecyl sulphate (SDS) (GRONOW & GRIFFITH, 1971), did not find significant qualitative or quantitative' differences. Similarly, BURDMAN (1972) reported good agreement between the N H P banding patterns of 1-and 8-day-old rat brain separated on SDS-containing polyacrylamide gels. Differences were, however, observed in the banding patterns of the N H P from 7day-old vs adult rat brain (SZIJAN & BURDMAN, 1973).…”

“…The NHP fraction has been shown to contain enzymes involved in DNA metabolism (PATEL et al, 1967;WANG, 1968;OCONNOR, 1969). Comparing the protein content of brain nuclei of I-and 8-day-old rats, BURDMAN (1972) found an increase in the total amount of nuclear proteins per brain a t 8 days after birth, assuming identical yields of nuclei in the preparations from neonatal and 8-day-old brain. This higher nuclear protein content was essentially due to saline-soluble proteins in nuclei purified through sucrose but without further Triton treatment.…”

The nuclear localization of a putative neurotransmitter receptor

“…The RNA/DNA ratio of the nuclear pellet was 0.56 and the protein/DNA ratio was 8.34 (results of two independent determinations within 5% of each other). Since purified brain nuclei have been reported to have an RNA/DNA ratio of0.4 and a protein/ DNA ratio of 4.8 (8,17), our preparation of nuclei was estimated to be 58-71% pure. Since we found the protein/DNA ratio of whole brain to be 96 (mean of two determinations within 5% of each other), this represents an 11.5-fold purification.…”