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PubMedDate not supplied

Peroxisomal biogenesis disorder: comparison of conventional MR imaging with diffusion-weighted and diffusion-tensor imaging findings.

BACKGROUND AND PURPOSE: Peroxisomal biogenesis disorders (PBDs) refer to a group of disorders of peroxisomal biogenesis causing neuronal migration disorder, delayed myelination, and demyelination. The aim of this study was to evaluate the added value of diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) compared with that of conventional T2-weighted imaging in assessing the extent of white matter damage in patients with PBDs. METHODS: Three patients (aged 12, 16, and 80 months) with PBD (type 1 protein targeting sequence [PTS1]) and three age-matched control subjects underwent MR imaging on a 1.5-T system. The protocol included axial T2-weighted, DWI, and DTI sequences. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) changes were calculated using regions of interest at several predefined white matter areas and compared with those of age-matched control subjects. Color-coded maps were obtained to visualize the range of FA values. RESULTS: On the T2-weighted images, one patient revealed severe hypomyelination throughout the brain; the two other patients showed focal abnormal high-signal-intensity areas. All patients had significantly decreased FA values in white matter areas that appeared abnormal on the T2-weighted images. In two of the three patients, significant FA reduction was also found in normal-appearing white matter. The ADC values of the patients were significantly increased compared with those of the age-matched controls. CONCLUSION: Although based on a small number of patients, our data suggest that DWI and DTI can be used to characterize and quantify white matter tract injury in patients with PBD-PTS1. Furthermore, our data suggest that these techniques have the potential to identify neurodegenerative changes not yet visible on T2-weighted images.

Child↗
PubMed2005

Small RNAs: classification, biogenesis, and function.

Eukaryotes produce various types of small RNAs of 19-28 nt in length. With rapidly increasing numbers of small RNAs listed in recent years, we have come to realize how widespread their functions are and how diverse the biogenesis pathways have evolved. At the same time, we are beginning to grasp the common features and rules governing the key steps in small RNA pathways. In this review, I will summarize the current classification, biogenesis, action mechanism and function of these fascinating molecules.

Animals↗
PubMed2005

[Structural, functional and genetic aspects of peroxisome biogenesis].

Intracellular organelles, peroxisomes, occur in cells of most eukaryotic species. Human severe congenital disorders are associated with defective assembly and functioning of peroxisomes, which partly explains the attention of researchers paid to peroxisome biogenesis. It has been shown that peroxisomes are involved in the realization of eukaryotic developmental programs (in particular, neuroblast differentiation and postembryonic development). Cytobiochemical and electron-microscopic studies of mutations involving peroxisomes showed that the primary role in peroxisome biogenesis is played by synthesis of proteins (peroxins) and their transport and incorporation into peroxisome membranes. More than 30 peroxin-encoding genes have been examined. These genes are synthesized on free polysomes and transported into peroxisomes by means of specific signaling peptides, PTS1, PTS2, and PTS3. The import of matrix proteins depends on at least two shuttle receptor proteins, Pex5p and Pex7p. Some proteins regulating peroxisome proliferation in cells have been identified.

Animals↗
PubMedDate not supplied

[Changes in the composition of anionic membrane phospholipids influence the protein secretion and biogenesis of cell envelope in Escherichia coli].

The secretion of alkaline phosphatase (PhoA) and peculiarities of biogenesis of the cell envelope were studied in Escherichia coli strains HD30/pHD 102 and HDL11 with controlled synthesis of anionic phospholipids, phosphatidylglycerol, and cardiolipin. Inactivation of the pgsA gene encoding the synthesis of anionic phospholipids or changes in the regulation of its expression by an environmental factor caused changes in the metabolism and composition of membrane phospholipids, which resulted in a decrease in the secretion of alkaline phosphatase through the cytoplasmic membrane and an increase in PhoA secretion from the periplasm into the culture medium. A conforming increase was observed in exopolysaccharide secretion, as well as a decrease in the contents of lipopolysaccharide and lipopolyprotein of the outer membrane that determine the membrane barrier properties. The results obtained testify that anionic phospholipids play a significant role in protein secretion and are probably involved in the interrelation between the protein secretion and biogenesis of cell envelope components.

Alkaline Phosphatase↗
PubMed2005

Reverse transcriptase inhibitors alter uncoupling protein-1 and mitochondrial biogenesis in brown adipocytes.

OBJECTIVE: Human adipose depots contain remnant brown adipocytes interspersed among white adipocytes, and disturbances of brown with respect to white adipocyte biology have been implicated in highly active antiretroviral therapy (HAART)-induced lipomatosis. Brown adipocytes express the uncoupling protein-1 (UCP1) and contain a large number of mitochondria, potential targets of HAART toxicity. The aim of this study was to evaluate the effects of reverse transcriptase inhibitors (RTIs) on primary brown adipocytes differentiated in culture. DESIGN AND METHODS: We analysed the effects of RTIs, nucleoside analogues (NRTIs: stavudine, zidovudine, didanosine and lamivudine) and non-nucleoside analogues (NNRTIs: nevirapine and efavirenz), on differentiation, mitochondrial biogenesis and gene expression in brown adipocytes. RESULTS: None of the NRTIs altered brown adipocyte differentiation whereas NNTRIs had differing effects. Efavirenz blocked lipid deposition and expression of adipose marker genes but nevirapine induced lipid accumulation and adipose gene expression, promoted mitochondrial biogenesis and increased UCP1. Stavudine, zidovudine and didanosine reduced mitochondrial DNA (mtDNA) content. However, mitochondrial genome expression was only impaired in didanosine-treated adipocytes. Stavudine, but not zidovudine, induced expression of the mitochondrial transcription factors and this may explain compensatory mechanisms for the depletion of mtDNA by up-regulating mtDNA transcription. Stavudine caused a specific induction of UCP1 gene expression through direct interaction with a retinoic acid-dependent pathway. CONCLUSIONS: Specific disturbances in brown adipocytes in adipose depots may contribute to HAART-induced lipomatosis. Mitochondrial depletion does not appear to be the only mechanism explaining adverse effects in brown adipocytes because there is evidence of compensatory mechanisms that maintain mtDNA expression, and the expression of the UCP1 gene is specifically altered.

Adipose Tissue, Brown↗
PubMed2005

Paracoccidioides brasiliensis RNA biogenesis apparatus revealed by functional genome analysis.

The RNA biogenesis machinery of Paracoccidioides brasiliensis was assessed by comparative analyses of PbAESTs (P. brasiliensis assembled expressed sequence tags (ESTs)) with sequences from Saccharomyces cerevisiae MIPS database. PbAESTs related to almost all categories of S. cerevisiae RNA biogenesis were found. Two of the 12 S. cerevisiae RNA Pol II core subunits, Rpb3 and Rpb7, were found, probably reflecting the growth phase from which the cDNA libraries used in ESTs generation were constructed, as well as the low abundance of some of these transcripts. We have also found orthologs to TATA-box-binding protein (TBP), and at least one subunit of each TBP-associated factors (TFII) in P. brasiliensis transcriptome, except TFIIB. Genes associated to the chromatin remodeling complex, as well as transcription factors probably involved in the control of genes associated to a sexual cycle and virulence, were also identified. With respect to the pre-mRNA processing, 65 PbAEST orthologs to S. cerevisiae basal splicing machinery and 21 orthologs of 5'- and 3'-end formation processes were found. Components involved in RNA interference were detected, suggesting that this gene expression regulation mechanism is probably used by P. brasiliensis. Twelve PbAESTs related to Pol I and Pol III machineries were assigned as S. cerevisiae orthologs. Finally, 25 and 10 PbAESTs associated to rRNA and tRNA processing, respectively, were detected. Taken together, our results enable us to depict, for the first time, a global view of transcription and RNA processing in P. brasiliensis.

Expressed Sequence Tags↗
PubMed2005

The chaperone-usher pathway of bacterial adhesin biogenesis -- from molecular mechanism to strategies of anti-bacterial prevention and modern vaccine design.

The chaperone-usher system determines the biogenesis of surface-exposed adhesive structures responsible for virulence of many Gram-negative bacteria. Investigations of the last 20 years have resolved the mechanism of this pathway on a structural level for different species of pathogenic bacteria. The purpose of this review is to present the molecular mechanisms of the biogenesis of adhesive structures assembled via the chaperone-usher pathway. The obtained mechanistic data allow one to propose potential strategies of anti-bacterial action. Additionally, the specific properties of the polymeric adhesive structures (pili and fimbriae) of the chaperone-usher system allow their use as effective and safe recombinant vaccines carrying foreign epitopes in thousands of copies on bacterial cell surface.

Adhesins, Bacterial↗
PubMedDate not supplied

[New approach to reveal genes that control cell wall biogenesis of the yeast Saccharomyces cerevisiae].

The Mcd4 protein of Saccharomyces cerevisiae is probably involved in addition of the phosphoethanolamine moiety to the first mannose residue of the glycosylphosphatidylinositol precursor(s). However, significance of this modification is unclear. Besides, functions of the MCD4 gene also is not completely clear, since mutations in this gene may have pleiotropic manifestations, which are not obviously related to the glycosylphosphatidylinositol biosynthesis. To clarify the functions of Mcd4p we have performed a search for genes whose mutations are lethal or semilethal in combination with the ssu21 mutation in MCD4. In total, we have isolated six mutations some of which cause sensitivity to SDS and/or calcofluor white. Genes which are able to complement two of these mutations were cloned. They were MNN9 which encodes protein involved in formation of outer chains of the N-linked glycans of secretory proteins and GWT1, encoding the protein of the endoplasmic reticulum involved in the glycosylphosphatidylinositol biosynthesis. The results obtained indicate that in both cases growth inhibition was caused by defect of cell wall biogenesis and alteration of folding of secretory proteins. Search for mutations that lethal in combination with the ssu21 is an effective approach to reveal genes involved in the control of cell wall biogenesis.

Adaptor Proteins, Signal Transducing↗
PubMed1990

Biogenesis of vacuolar membrane glycoproteins of yeast Saccharomyces cerevisiae.

To investigate the biogenesis of the yeast vacuole, we have sought novel marker proteins localized to the vacuolar membrane. Glycoproteins were prepared from vacuolar membrane vesicles by concanavalin A-Sepharose column chromatography and used to raise monoclonal antibodies. The antibodies obtained recognize several vacuolar proteins that have N-linked oligosaccharide chains. A set of the antibodies reacts with a vacuolar glycoprotein with a major molecular species of 72 kDa (vgp72), which appears to associate peripherally with the vacuolar membrane. The biosynthesis of vgp72 has been examined in detail by pulse-chase experiments and by analyses using various secretory mutants (sec18, sec7, and sec1) and a vacuolar protease mutant (pep4). vgp72 first appears in the endoplasmic reticulum as a 74-kDa species and is quickly modified in the Golgi apparatus to two distinct species: a 79-kDa form, and a heterogeneously glycosylated form (90-150 kDa). Subsequently, both species are proteolytically processed in the vacuole giving rise to a 72-kDa species as well as heavily glycosylated form. Thus, the biogenesis of vgp72 utilizes the early part of the secretory pathway as is the case of vacuolar soluble enzymes. A unique feature is that two species that are different in the extent of glycosylation appear to follow the same destination to the vacuolar membrane.

Acetylglucosaminidase↗
PubMed1987

Biogenesis of glycophorin A in K562 human erythroleukemia cells.

A monoclonal antibody (mAb-233) directed against an epitope in the nonglycosylated carboxyl-terminal region of human erythrocyte glycophorin A (GPA) was used in combination with metabolic labeling, the modification of N- and O-linked oligosaccharide processing by tunicamycin and monensin, and digestions with neuraminidase and O-glycanase to elucidate the pathway of GPA biogenesis in K562 human erythroleukemia cells. Cell-surface GPA is derived from two obligatory precursors in a stepwise manner. The initial GPA precursor has a Mr of 27,000 and appears to contain one N-linked high mannose oligosaccharide chain. In tunicamycin-treated cells, the initial precursor is similar in size (Mr = 24,000) to deglycosylated GPA from human erythrocytes. The 27-kDa initial precursor is rapidly converted to a transient 31-kDa intermediate by the addition of N-acetylgalactosamine residues to serine/threonine hydroxyl groups. Subsequent maturation involves the conversion of the high mannose chain to a complex-type oligosaccharide and the concomitant addition of galactose and sialic acid to internal N-acetylgalactosamine residues to extend the O-linked chains. These results define a single, stepwise processing pathway for the generation of all cell-surface GPA molecules and document for the first time the occurrence of both a unique initial precursor that contains a high mannose N-linked oligosaccharide chain but no O-linked sugars and a transient intermediate that appears to contain the same N-linked group and N-acetylgalactosamine at multiple serine/threonine residues. The properties of the intracellular GPA precursors and the relatively simple nature of the processing pathway reported herein contrast markedly with the characteristics of three intermediates and the complexity of two independent pathways in previously postulated schemes for GPA biogenesis (Gahmberg, C. G., Jokinen, M., Karhi, K. K., Kampe, O., Peterson, P. A., and Andersson, L. C. (1983) Methods Enzymol. 96, 281-298; Jokinen, M., Andersson, L. C., and Gahmberg, C. G. (1985) J. Biol. Chem. 260, 11314-11321).

Antibodies, Monoclonal↗
PubMed1989

A role for membrane potential in the biogenesis of cytochrome c oxidase subunit II, a mitochondrial gene product.

Subunit II of yeast cytochrome c oxidase is synthesized on mitochondrial ribosomes as a precursor containing a transient NH2-terminal presequence and is inserted into the mitochondrial inner membrane from the matrix side. Using an optimized in vitro mitochondrial translation system (McKee, E.E., and Poyton, R. O. (1984) J. Biol. Chem. 259, 9320-9331), we have examined the requirement for an electrochemical potential (delta mu H+) across the inner mitochondrial membrane during subunit II biogenesis. When mitochondrial gene products are synthesized under conditions that prevent formation of a normal delta mu H+, accumulation of unprocessed subunit II (pre-II) occurs. The majority of pre-II generated in this way is inserted into the lipid bilayer, as judged by resistance to extraction with 0.1 M Na2CO3. Therefore, it appears that a delta mu H+ is required for the normal biogenesis of subunit II, and that the delta mu H+ is required for a function other than the insertion of pre-II into the lipid bilayer of the inner membrane.

DNA, Mitochondrial↗
PubMed1989

Effect of dimethyl sulphoxide on mitochondrial biogenesis in regenerating rat liver and Saccharomyces cerevisiae.

Effect of dimethyl sulphoxide (DMSO) on mitochondrial biogenesis in regenerating rat liver and cells of Saccharomyces cerevisiae during aerobiosis has been studied by monitoring the cytochrome oxidase activity. A single dose of DMSO (275 mg/100-125 g body wt) to normal rats stimulated cytochrome oxidase activity in liver mitochondria while the same dose to partial hepatectomized rats inhibited the enzyme activity. Administration of low dose of DMSO (92 mg/100-125 g body wt) to partial hepatectomized rats did not alter the enzyme activity. Anaerobic cells of S. cerevisiae on aerobiosis for 2 hr attained cytochrome oxidase activity level on par with aerobic cells. Inclusion of DMSO (275 mg/100 ml) in the growth medium of S. cerevisiae during respiratory adaptation exerted partial inhibitory effect on the formation of cytochrome oxidase at 2 hr period, while the 10-fold concentration inhibited the enzyme formation completely. However, the inhibitory effect of DMSO on enzyme formation was abolished on prolonged growth (18 hr and above), while these doses had no influence on cytochrome oxidase in aerobic cells of S. cerevisiae. The results imply that DMSO may be exerting its effect on the assembly of subunits into active enzyme complex during mitochondrial biogenesis.

Animals↗
PubMed1989

Chinese hamster ovary cell mutants defective in peroxisome biogenesis. Comparison to Zellweger syndrome.

We have previously reported the isolation of Chinese hamster ovary (CHO) cell mutants that are defective in the biosynthesis of plasmalogens, deficient in at least two peroxisomal enzymes (dihydroxyacetonephosphate (DHAP) acyltransferase and alkyl-DHAP synthase), and in which catalase is not found within peroxisomes (Zoeller, R. A., and Raetz, C. R. H. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 5170). We now provide further evidence that three such strains are more generally defective in peroxisome biogenesis. Electron microscopic cytochemistry revealed that the mutants did not contain recognizable peroxisomes. However, immunofluorescence microscopy using an antibody directed against peroxisomal integral membrane proteins revealed the presence of peroxisomal membrane ghosts resembling those seen in cells of patients suffering from one of the human peroxisomal disorders, Zellweger syndrome. Immunoblot analyses, using antibodies specific for peroxisomal matrix proteins, demonstrated deficiencies of peroxisomal proteins in the mutant CHO cells that were similar to those in Zellweger syndrome. Fusion of a CHO mutant with fibroblasts obtained from Zellweger patients resulted in restoration of peroxisomal dihydroxyacetonephosphate acyltransferase and peroxisomal acyl-coenzyme A oxidation activities. The hybrid cells also regained the ability to synthesize plasmenylethanolamine. Moreover, normal peroxisomes were seen by immunofluorescence in the hybrid cells. These results indicate that the hybrid cells have recovered the ability to assemble peroxisomes and that, although the mutant CHO cells are biochemically and morphologically very similar to cells from patients with Zellweger syndrome, the genetic lesions are distinct. Our somatic cell mutants should be useful in identifying factors and genes involved in peroxisome biogenesis and may aid the genetic categorization of the various peroxisomal disorders.

Acyl Coenzyme A↗
PubMed1988

[Nuclear and mitochondrial genes in the biogenesis of Saccharomyces cerevisiae mitochondria].

The mechanisms of interaction of nuclear and mitochondrial genes in biogenesis of mitochondria are discussed in this review. Brief characterization of yeast mitochondrial genes and their products is presented. The mechanism of nuclear and mitochondrial control of expression of the mosaic genes in mitochondria is described. The data on the processing of imported mitochondrial proteins synthesized on cytoplasmic ribosomes are presented. The possibility of existence of common proteins encoded for by common genes and possessing similar functions in the cytoplasm and mitochondria is discussed. A hypothesis is put forward considering the role of common proteins in coordination of nuclear and mitochondrial genes' expression in biogenesis of mitochondria.

DNA, Fungal↗
PubMed1977

[Incorporation of 32P into membrane phospholipids during chloroplast biogenesis].

The composition of membrane phospholipids during chloroplast biogenesis was studied. The maximal level of phosphatidic acid was observed in the membrane fraction of proplastids. Phosphatidylglycerol was found to be the most abundant phospholipid component of grana thylakoids. The evidence from the in vivo experiments indicates that phosphatidic acid and phosphatidylglycerol incorporate the 32P label at a high rate at all stages of the chloroplast biogenesis. It is concluded that plastids are the site of the phosphatidylglycerol biosynthesis in the plant cell.

Chloroplasts↗
PubMed1982

Time course of peroxisome biogenesis during adaptation to mild hyperthyroidism in rat liver: a morphometric/stereologic study by electron microscopy.

The subcellular reaction pattern of the peroxisome compartment in rat liver cells has been studied after thyroid hormone administration for 1, 3, 5, 8, and 15 days (20 micrograms of 3, 3', 5'-triiodothyronine (T3) per 100 gm. of body weight per day). Mild hyperthyroidism caused by T3 resulted in the enlargement of the peroxisome volume fraction. This was achieved exclusively by an increase in organelle number (31 x 10(9) +/- 1.5 x 10(9) per 1 cu. cm. per cu. cm. of cytoplasm in controls), since the average organelle volume (0.27 +/- 0.02 cu. micrometer in controls) was simultaneously reduced. The remodeling of the peroxisome compartment was, for the most part, completed on day 3 and consisted of a first preliminary doubling of peroxisome numbers after 1 day, followed by a second doubling on day 3. Each doubling was accompanied by a one-third reduction in the average organelle volume. Peroxisome biogenesis due to T3 resulted in (1) the formation of microperoxisomes, consisting of small profiles, lacking the core-structure and (2) an increase of peroxisomes arranged in clusters. Cluster types with two to three profiles appeared from the beginning of biogenesis, whereas clusters with four or more profiles were mostly observed at the end. The latter was taken as an indication of a late phase of adaptation of the peroxisome compartment to hyperthyroidism, following a rapid early phase, mainly expressed on the organellar level and completed for the most on day 3. The parallel response of peroxisomes and mitochondria, as seen by the simultaneous enlargement of the fractional volume of both compartments, is taken as an indication of a close functional relationship of both organelle systems under stimulated cellular respiration.

Adaptation, Physiological↗
PubMed1976

Biogenesis of matrix vesicles in cartilage growth plates.

Although the structure and function of cartilage matrix vesicles have been comprehensively documented in the literature, the method of vesicle production and export to the extra-cellular matrix is less well understood. The existing data are grouped into four general hypotheses of matrix vesicle biogenesis, with a consideration of the relative merits and weaknesses of each postulate. The hypotheses are: a) budding from cellular processes; b) extrusion of preformed structures; c) cellular degeneration and disintegration; and c)subunit secretion and extracellular assembly. Each of these possibilities offers conceptual advantages and disadvantages, so that it is difficult to adopt a monistic stance. Previous notions of vesicle biogenesis have derived from statis morphologic and analytical data, which are necessarily limiting when attempting to draw kinetic conclusions. Radiotracer studies of lipid synthesis and transport in cartilage lead to the conclusion that matrix vesicles in the growth plate are derived from chondrocytes; the present data favor the hypotheses of budding from cellular processes and/or subunit secretion with extracellular self-assembly.

Cartilage↗
PubMed1995

[Changes in biogenesis and secretion of periplasmic alkaline phosphatase, coded by the phoA gene included in the Escherichia coli DH1 plasmid].

Augmented synthesis of periplasmic alkaline phosphatase from E. coli DH1 coded by the phoA gene within the composition of plasmid pHI-7 results in alterations in the enzyme biogenesis, such as accumulation of intermediate enzyme forms corresponding to various stages of its posttranslational modification, and alternative localization. The cell cytoplasm was found to contain a large proportion of alkaline phosphatase precursors in the form of insoluble aggregates. The mature enzyme was detected in both the periplasm and the cultural fluid in the form three methazymes with an increased (as compared with the original strain) content of methazymes I and II. The cell envelope of E. coli DHI transformed by plasmid pHI-7 with the phoA gene differed from that of the original strain by an increased acid phospholipid (cardiolipin/phosphatidylglycerol) ratio as well as by increased distribution density of intramembrane particles on the surface of the cytoplasmic membrane facing the cytoplasm. Changes in the biogenesis of the enzyme during its augmented synthesis are due to disturbances in the equilibrium between the synthesis of polypeptide chains, on the one hand, and their translocation and processing, on the other, apparently as a result of restricted secretion sites and lack of inhibition of translation of secreted proteins in bacteria.

Alkaline Phosphatase↗