Hiroshi Ochiai

Analysis of N-linked oligosaccharide chains of glycoproteins on nitrocellulose sheets using lectin-peroxidase reagents

A rapid and convenient method was established for analysis of the N-linked carbohydrate chains of glycoproteins on nitrocellulose sheets. Proteins were separated by polyacrylamide gel electrophoresis, transferred to nitrocellulose sheets, reacted with peroxidase-coupled lectins, and detected by color development of the enzyme reaction. Four glycoproteins having N-linked oligosaccharide chains were used as test materials: Taka-amylase A (which has a high-mannose-type chain), ovalbumin (high-mannose-type chains and hybrid-type chains), transferrin (biantennary chains of complex type), and fetuin (triantennary chains of complex type and O-linked-type chains). Concanavalin A interacted with Taka-amylase A, transferrin, and ovalbumin but barely interacted with fetuin. After treatment of the glycoproteins on a nitrocellulose sheet with endo-beta-N-acetylglucosaminidase H, transferrin reacted with concanavalin A but Taka-amylase A and ovalbumin did not. Wheat germ agglutinin interacted with Taka-amylase A but not ovalbumin; therefore, they were distinguishable from each other. Fetuin and transferrin were detected by Ricinus communis agglutinin or peanut agglutinin after removal of sialic acid by treatment with neuraminidase or by weak-acid hydrolysis. Erythroagglutinating Phaseolus vulgaris agglutinin detected fetuin and transferrin. Thus, the combined use of these procedures distinguished the four different types of N-linked glycoproteins. This method was also applied to the analysis of membrane glycoproteins from sheep red blood cells. The terminally positioned sugars of sialic acid, alpha-fucose, alpha-galactose, and alpha-N-acetylgalactosamine were also detected with lectins from Limulus polyphemus, Lotus tetragonolobus, Maclura pomifera, and Dolichos biflorus, respectively.

Intranuclear disposition of exogenous DNA in vivo: silencing, methylation and fragmentation.

The intranuclear disposition of exogenous DNA is highly important for the therapeutic effects of the administrated DNA. Naked luciferase‐plasmid DNA was delivered into mouse liver by a hydrodynamics‐based injection, and the amounts of intranuclear plasmid DNA, luciferase, and its mRNA were quantitated at various time points. Methylation of the promoter of the luciferase gene was also analyzed. Expression efficiency from one copy of the exogenous DNA dramatically decreased over time, and the DNA was methylated and degraded into fragments. Unexpectedly, methylation of the intact plasmid DNA was low and did not increase over time. Rather, the fragmented DNA was methylated more frequently than the intact plasmid. These results suggest that the CpG methylation and the degradation of exogenous DNA, and its ‘silencing’, occurred in parallel in the nucleus.

Transient activation of transgene expression by hydrodynamics-based injection may cause rapid decrease in plasmid DNA expression

The intranuclear disposition of exogenous DNA is quite important for the therapeutic effects of the administered DNA. The expression efficiency from one copy of exogenous DNA delivered by hydrodynamics-based injection dramatically decreases over time, and this ‘silencing’ occurs without CpG methylation. In this study, naked luciferase-plasmid DNA was delivered into mouse liver by hydrodynamics-based injection, and modifications of the histones bound to the plasmid DNA were analyzed by a chromatin immunoprecipitation (ChIP) analysis. In addition, the effects of a second hydrodynamics-based injection on the expression from the plasmid DNA were examined. The ChIP analysis revealed that the modification status of histone H3 remained constant from 4u2009h to 4 weeks. Surprisingly, the injection of saline without DNA enhanced the luciferase expression from the preexisting DNA administered 4 and 14 days previously. Our results suggest that histone modification plays no role in the silencing. Instead, our data suggest that the transgene expression is activated by the hydrodynamics-based injection manipulation, and that the return from the activated status causes the silencing.

MFE1, a Member of the Peroxisomal Hydroxyacyl Coenzyme A Dehydrogenase Family, Affects Fatty Acid Metabolism Necessary for Morphogenesis in Dictyostelium spp.

ABSTRACT β-Oxidation of long-chain fatty acids and branched-chain fatty acids is carried out in mammalian peroxisomes by a multifunctional enzyme (MFE) or d-bifunctional protein, with separate domains for hydroxyacyl coenzyme A (CoA) dehydrogenase, enoyl-CoA hydratase, and steroid carrier protein SCP2. We have found that Dictyostelium has a gene, mfeA, encoding MFE1 with homology to the hydroxyacyl-CoA dehydrogenase and SCP2 domains. A separate gene, mfeB, encodes MFE2 with homology to the enoyl-CoA hydratase domain. When grown on a diet of bacteria, Dictyostelium cells in which mfeA is disrupted accumulate excess cyclopropane fatty acids and are unable to develop beyond early aggregation. Axenically grown mutant cells, however, developed into normal fruiting bodies composed of spores and stalk cells. Comparative analysis of whole-cell lipid compositions revealed that bacterially grown mutant cells accumulated cyclopropane fatty acids that remained throughout the developmental stages. Such a persistent accumulation was not detected in wild-type cells or axenically grown mutant cells. Bacterial phosphatidylethanolamine that contains abundant cyclopropane fatty acids inhibited the development of even axenically grown mutant cells, while dipalmitoyl phosphatidylethanolamine did not. These results suggest that MFE1 protects the cells from the increase of the harmful xenobiotic fatty acids incorporated from their diets and optimizes cellular lipid composition for proper development. Hence, we propose that this enzyme plays an irreplaceable role in the survival strategy of Dictyostelium cells to form spores for their efficient dispersal in nature.

A novel Dictyostelium Cdk8 is required for aggregation, but is dispensable for growth.

When Dictyostelium cells starve, they express genes necessary for aggregation. Using insertional mutagenesis, we have isolated a mutant that does not aggregate upon starvation and that forms small plaques on bacterial lawns, thus indicating slow growth. Sequencing of the mutated locus showed a strong similarity to the catalytic domain of cdc2‐related kinase genes. Phylogenetic analysis further indicated that the amino acid sequence was more close to cyclin‐dependent kinase 8 than to the sequence of other cyclin‐dependent kinases. Thus, we designated this gene as Ddcdk8. The Ddcdk8‐null cells do not aggregate and grow somewhat more slowly than parental cells when being shaken in axenic medium or laid on bacterial plates. To confirm whether these defective phenotypes were caused by disruption of this gene, the Ddcdk8‐null cells were complemented with DdCdk8 protein expressed from an endogenous promoter, but not an actin promoter, and when the complemented cells were then allowed to grow on a bacterial lawn, they began to aggregate as the food supply was depleted and finally became fruiting bodies. The results suggest that properly regulated DdCdk8 activity is essential for aggregation. Because, when starved, Ddcdk8‐null cells do not express the acaA transcripts required for aggregation, we deduce that Ddcdk8 is epistatic for acaA expression, indicating that the DdCdk8 products may regulate expression of acaA and/or other genes.

Antisense RNA Inhibition of the β Subunit of the Dictyostelium discoideum Mitochondrial Processing Peptidase Induces the Expression of Mitochondrial Proteins

We cloned and characterized a cDNA encoding the Dictyostelium discoideum β subunit of mitochondrial processing peptidase (Ddβ-MPP). Western blot analysis of the mitochondrial subfractions revealed that Ddβ-MPP is located in the mitochondrial matrix and membrane, whereas Ddα-MPP, another subunit of DdMPP, is located only in the matrix. Although expression of Ddβ-MPP mRNA is down-regulated during early development, the level of the Ddβ-MPP protein is constant throughout the Dictyostelium life cycle. In a transformant expressing the antisense RNA of the β-MPP gene, unexpectedly, the β-MPP protein increased about 1.8-fold relative to the wild type, and its mRNA increased 4.5-fold. Expression of other mitochondrial proteins, α-MPP and Cox IV, was also induced. These results suggest that antisense RNA inhibition of the β-MPP gene induces gene expression of mitochondrial proteins, presumably in a retrograde signaling manner. This is the pathway of the transfer of information from the mitochondria to the nucleus.

Spatial expression patterns of genes involved in cyclic AMP responses in Dictyostelium discoideum development

The spatial expression patterns of genes involved in cyclic adenosine monophosphate (cAMP) responses during morphogenesis in Dictyostelium discoideum were analyzed by in situ hybridization. Genes encoding adenylyl cyclase A (ACA), cAMP receptor 1, G‐protein α2 and β subunits, cytosolic activator of ACA (CRAC and Aimless), catalytic subunit of protein kinase A (PKA‐C) and cAMP phosphodiesterases (PDE and REG‐A) were preferentially expressed in the anterior prestalk (tip) region of slugs, which acts as an organizing center. MAP kinase ERK2 (extracellular signal‐regulated kinase‐2) mRNA, however, was enriched in the posterior prespore region. At the culmination stage, the expression of ACA, CRAC and PKA‐C mRNA increased in prespore cells in contrast with the previous stage. However, no alteration in the site of expression was observed for the other mRNA analyzed. Based on these findings, two and four classes of expression patterns were catalogued for these genes during the slug and culmination stages, respectively. Promoter analyses of genes in particular classes should enhance understanding of the regulation of dynamic and coordinated gene expression during morphogenesis.

Identification of a novel all-cis-5,9,12-Heptadecatrienoic acid in the cellular slime moldPolysphondylium pallidum

The all-cis-5,9,12-heptadecatrienoic acid was identified in the cellular slime moldPolysphondylium pallidum. The structural elucidation was accomplished by capillary gas chromatography, argentation thin-layer chromatography, and gas chromatography/mass spectrometry. This fatty acid has not been reported previously.

Fatty acid composition of the cellular slime mold Polysphondylium pallidum.

The cellular slime mold Polysphondylium pallidum was grown upon Escherichia coli B/r, and the fatty acid compositions of total lipids obtained from vegetative amebae and aggregation-competent cells were compared. Fatty acids isolated from vegetative cells included C-17 and C-19 cyclopropane fatty acids and also straight-chain, saturated fatty acids. The cyclopropane fatty acids were derived from the ingested bacteria. Development of amebae to aggregation-competent cells was accompanied by a substantial decrease in saturated cyclopropane fatty acids and a concomitant increase in unsaturated fatty acids and unsaturated cyclopropane fatty acids, mostly as 18∶3 (5,9,12). We report here the fatty acid composition and identify the occurrence of Δ5 desaturation of cyclopropane fatty acids, namely, 9,10-methylene 5-hexadecenoic acid and 11,12-methylene 5-octadecenoic acid. These fatty acids have not been reported previously in the related species Dictyostelium discoideum, which also feeds on E. coli B/r and has Δ5-desaturation activity.

Positive Feedback System Provides Efficient and Persistent Transgene Expression

The two-step transcriptional amplification (TSTA) system, using artificial transcription factors, effectively enhances transgene expression. In this study, a TSTA system-based positive feedback system was developed to achieve efficient and persistent transgene expression. A fusion protein of the sequence-specific DNA binding domain of yeast GAL4 and the transcriptional activation domain of herpes simplex virus VP16 (GAL4-VP16) was used as an activator to amplify the expression of the luciferase reporter gene. It was found that the introduction of five tandem copies of the GAL4 recognition sequence (G5) into both the upstream and downstream regions of the expression cassette synergistically enhanced the transgene expression. The upstream and downstream G5 sequences were introduced into the expression cassette of the activator itself, and into that of the reporter, to form the positive feedback loop that enabled continuous activator expression. This positive feedback system maintained the expression levels of the reporter for 4 days in HeLa cells and for a week in mouse liver, while those from the usual plasmids decreased by 30- and 50-fold, respectively. These results constitute the first evidence that the positive feedback system is a useful method for long-term transgene expression in cultured cells and in vivo. This system would be applicable to gene therapy, in vivo imaging, and biotechnology.