Labeling of RNA in young and adult rat brain: evidence for different RNA processing

RNA synthesis in isolated mitochondria from brain cortex, cerebellum and stem: evidence of different transcriptional rates

1. A system for studying RNA synthesis in isolated sheep brain mitochondria was set up to investigate the transcriptional activity of different brain regions (cortex, cerebellum and brain stem). In this system, mitochondrial DNA is transcribed and RNA processed in a way that faithfully reproduces the in vivo process. 2. The comparison of the electrophoretic patterns of the mitochondrial DNA transcription products showed that although they were qualitatively similar, there were large differences in the rate of mitochondrial DNA transcription of the three regions studied, cerebellum and brain stem showing transcriptional rates which were 34 and 18% respectively of that of cerebral cortex.

Analysis of polyadenylated RNA from brain synaptosomes and mitochondria

We have isolated RNA from sheep brain synaptosomes and mitochondria separated by an aqueous two-phase system composed of dextran and poly(ethylene glycol). RNA was fractionated through oligo(dT)-cellulose columns and analyzed by electrophoresis through agarose slab gels containing methylmercuric hydroxide and stained with ethidium bromide. The electrophoretic patterns of the poly(A)-containing RNA fraction from synaptosomes and mitochondria are very similar although some high molecular weight RNA species, clearly visible in the synaptosomal fraction, are scarcely detected in the mitochondrial preparations. The electrophoretic analysis of a cleaner RNA preparation from digitonin-treated free mitochondria (mitoplasts) showed that all the poly (A)-RNA species of the synaptosomal preparation are also present in mitoplast. These results strongly suggest that all the discrete poly(A)-RNA species identified in brain synaptosomes are of mitochondrial origin.

Effect of epidermal growth factor on the labeling of the various RNA species and of nuclear proteins in primary rat astroglial cell cultures

This study investigated the effects of epidermal growth factor (EGF) on the labeling of various RNA species and of nuclear proteins in primary rat astroglial cell cultures. After 12 hours of EGF treatment in serum-free medium or chemically defined medium, significant increase in RNA labeling, and also in acid-soluble radioactivity and RNA content, was observed. The ratio RNA/DNA was significantly higher in EGF-treated cultures compared with controls. Ribosomal RNAs (28S and 18S), polyadenylated, and nonpolyadenylated RNAs showed a higher specific radioactivity in EGF-treated cultures. Among the nuclear proteins, the labeling of basic proteins was enhanced by EGF treatment, whereas that of total nuclear acidic protein (NHPs) was less modified, except for some NHPs separated by gel electrophoresis with a molecular weight (MW) approximately 95-83 and 44 kd, which were significantly more labeled in EGF-treated cultures.

Differential effects of axotomy on immature and mature hamster facial neurons: a tritiated-uridine autoradiographic study

In this study, tritiated-uridine incorporation was autoradiographically examined following axotomy of hamster facial motor neurons (HFMN) at the critical development age of 15 days postnatal and in the adult. The postoperative times selected were 0.5, 1, 2, and 4 days. In the 15-day operative series, no changes in incorporation were observed at any of the postoperative times, except at 4 days postoperative, when there was a decrease in tritiated-uridine incorporation in the axotomized neurons relative to the controls. In the adult operative series there were no changes in incorporation at 0.5 or 1 day postoperative, relative to the controls. At 2 days postoperative in the adult, there was a transient increase in tritiated-uridine incorporation that returned to control levels by 4 days postoperative. When axotomized and control cytoplasmic/nuclear grain densities were compared, no changes were found in either operative series. These results of the time course of axotomy-induced changes in RNA synthesis in HFMN corroborate our previous findings of an age-dependent reactive sequence in HFMN and lend support to the hypothesis that the young neurons are synthesizing at peak capacity related to final growth and cannot be stimulated further by axotomy. As discussed, the transient increase in RNA levels in the adult, the lack of any changes in the rate of transfer of RNA from the nucleus to the cytoplasm, and the decrease in RNA levels in the 15-day neurons may be related to the presence of an unusual intranucleolar body within the nucleolus of HFMN that contains ribosomal precursors.

Ultrastructural changes in the nucleoplasm of hamster facial neurons during a postnatal maturation period

Changes in the characteristics of the nucleoplasm were examined in young hamster facial motoneurons of 15 and 20 days postnatal age and in the adult (100 days postnatal age) at both the light and electron microscope levels. In toluidine-blue stained 1-micron thick sections, a progressive increase in basophilic islands within the nucleoplasm occurred during maturation. Ultrastructural changes that were observed during final development included a transition from a homogeneous, 'filled-in' appearing nucleoplasm to a clumped-appearing nucleoplasm. This process principally involved the formation of distinct clusters of interchromatin granules that was associated with a loss of fine fibrils, an increase in clear spaces between intervening fibrillar and granular material, and an increase in small scattered clumps of heterochromatin. These changes in both ribonucleoprotein (RNP)-and DNA-containing nuclear constituents (interchromatin granules and heterochromatin, respectively) occurred during a postnatal maturational period previously demonstrated to involve other alterations in nuclear structures. It is interpreted that these cytomorphic changes in the nucleoplasm reflect an underlying metabolic shift at the transcriptional level during the transition from an actively growing neuron to an adult functioning neuron.

Effect of hypothyroidism on the labeling of the various RNA species in developing rat brain

The effect of hypothyroidism on the vitro incorporation of [3H]uridine into different RNA species in tissue slices of rat cerebral hemispheres at 5, 10, 15, and 21 days of age has been investigated. Gel electrophoresis analysis of total, nuclear and microsomal RNA was also accomplished. The results obtained indicate that RNA labeling is differently influenced by hypothyroidism at the various ages examined. RNA labeling is not significantly affected at 5 days of age while at later ages and especially at 21 days it is higher in hypothyroid rats compared to the controls. Moreover distinct differences at the various ages in the transport of newly synthesized RNA from the nucleus to the cytoplasm in the two groups of animals were found. These results are in agreement with the hypothesis that thyroid hormone deficiency causes a delay of the processes of cell proliferation and differentiation in developing rat brain.

RNA synthesis in neuronal and glial cell nuclei from rat cerebral hemispheres during early postnatal development

RNA synthesis in rat cerebral hemispheres at 1, 5, and 10 days of age and the relative contribution brought by neuronal and glial nuclei to RNA synthesis was investigated. The experiments were carried out both in vivo (by i.p. injection of [3H]uridine) and in vitro (either by incubation of tissue slices with [3H]uridine or by determination of RNA polymerase activities). The labeling of RNA decreases from 1 to 10 days of age both in vivo and in vitro; the decrease is of the same extent in neuronal and glial nuclei. RNA polymerase activity Mg2+-dependent does not change significantly from 1 to 10 days of age either in total, in neuronal, or in glial nuclei, whereas the Mn2+-dependent activity increases significantly over the same developmental period studied. The significance of RNA polymerase assay as an index of in vivo RNA synthesis is discussed.