Analysis of polyadenylated RNA from brain synaptosomes and mitochondria

Autonomous regulation in mammalian mitochondrial DNA transcription

The regulation of the oxidative phosphorylation system (OXPHOS) biogenesis in eukaryotic cells is unique since it involves the expression of two genomes, the mitochondrial DNA (mtDNA) and the nuclear DNA (nDNA). The considerable effort done in collecting information on the factors that influence the expression of the genes encoded in mtDNA and nDNA has revealed that a multiplicity of regulatory options are available in mammalian cells to perform this task. Thus, at least three archetypal situations can be distinguished: mitochondrial proliferation, mitochondrial differentiation, and mitochondrial local tuning (MLT). Each of them seems to be predominantly under the control of specific strategies of regulation, although the description of the detailed molecular mechanisms involved is still in its beginnings. In the present review, we focus on the evidence supporting the existence of mechanisms for autonomous regulation of mtDNA transcription and its role in the integrated regulation of the OXPHOS system biogenesis.

Analysis of the transcription products of the rainbow trout (Oncorynchus mykiss) liver mitochondrial genome: detection of novel mitochondrial transcripts

We have isolated and, by electrophoresis, using agarose slab gels in the presence of methylmercury hydroxide, analyzed the mitochondrial RNA content of the liver of rainbow trout. The RNAs corresponding to most of the mitochondrial DNA-encoded genes have been identified. Furthermore, among the transcription products we have also identified the nature of the RNA 8 previously described in human mitochondria, and detected a novel transcript that may represent the mRNA for ND6.

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.

Evaluation of RNAs present in synaptodendrosomes: dendritic, glial, and neuronal cell body contribution

"Synaptodendrosomes" are subcellular fractions that contain pinched-off axon terminals and dendrites. These fractions are a potential source of RNAs that are localized in dendrites. However, these fractions may also contain RNAs that are seen in situ in neuronal cell bodies and glia. To evaluate whether synaptodendrosomes could be used as a source of dendritic RNA, we studied the RNA content of this fraction as compared with RNA isolated from total forebrain and a cell body-enriched fraction. RNA was analyzed by gel electrophoresis, oligo-dT chromatography, and northern blot hybridization. RNA from synaptodendrosomes contained a greater proportion of low-molecular-weight nonpolyadenylated RNAs. RNAs known to be present in dendrites (mRNA for the alpha subunit of the calcium/calmodulin-dependent protein kinase II and the polymerase III transcript BC1) were detected in synaptodendrosomes; RNAs that are restricted to neuronal and glial cell bodies (mRNAs for the 68-kDa neurofilament protein, 43-kDa growth-associated protein, beta-tubulin, and beta-actin) were present only at low levels. However, the mRNA for glial fibrillary acidic protein (seen in situ in glial cell bodies and processes) was present at high levels in the synaptodendrosomes. These results support and extend previous studies indicating that a limited subset of mRNAs is present in neuronal and astrocyte processes and reveal that both of these types of mRNAs are present in synaptodendrosomes. Thus, synaptodendrosomes may be useful as a source of dendritic RNAs, but it will be necessary to develop strategies to subtract mRNAs present in astroglial processes.

Specific increase of a mitochondrial RNA transcript in chronic ethanol-fed rats

An in vitro transcription system utilizing isolated mitochondria has been used to study the effect of chronic ethanol consumption on liver mitochondrial DNA transcription. The results obtained showed an overall increase of RNA synthesis and a dramatic accumulation of a discrete polyadenylated RNA species. This effect is a consequence of the chronic ethanol consumption since these changes do not occur when isolated control mitochondria are incubated in the presence of ethanol.

Molecular characterization and cloning of sheep mitochondrial DNA

Mitochondrial DNA from the liver of a single Rasa Aragonesa sheep has been isolated and characterized. The size of the genome, determined by restriction enzyme analysis, was found to be 16.58 kbp. The cleavage sites for the restriction endonucleases BamHI, HindIII, EcoRI, BglII, PvuII, BstEII and PstI were mapped, and the gene organization deduced through heterologous hybridization using different cloned fragments of the rat mitochondrial genome. Fragments representative of the entire sheep genome were cloned in plasmid vectors pGEM3Z and pUN121.

Estimation of the chloramphenicol and cycloheximide inhibition of protein synthesis in brain cholinergic synaptosomes

Cholinergic synaptosomes have been prepared from sheep brain cortex by means of an immunoaffinity method using a specific anti-(Chol I) antiserum. The [14C]leucine incorporation into proteins of this preparation shows a low cycloheximide and a high chloramphenicol sensitivity. This fact suggests that the mitochondrial protein synthesis system is the only one present in this fraction.

Analysis of polyadenylated RNA from human heart mitochondria

The content of the mitochondrial poly(A)-RNA fraction of human heart has been analyzed by electrophoresis through agarose slab gels in the presence of methyl mercury hydroxide and staining with ethidium bromide. It is possible to identify all the heavy strand coded mRNAs in the electrophoretic pattern. This pattern is qualitatively similar to that obtained from the mitochondria of cells cultured in vitro (HeLa cells), although differences in the relative amount of some components have been detected.