α-Synuclein in filamentous inclusions of Lewy bodies from Parkinson’s disease and dementia with Lewy bodies

Lewy bodies and Lewy neurites are the defining neuropathological characteristics of Parkinson’s disease and dementia with Lewy bodies. They are made of abnormal filamentous assemblies of unknown composition. We show here that Lewy bodies and Lewy neurites from Parkinson’s disease and dementia with Lewy bodies are stained strongly by antibodies directed against amino-terminal and carboxyl-terminal sequences of α-synuclein, showing the presence of full-length or close to full-length α-synuclein. The number of α-synuclein-stained structures exceeded that immunoreactive for ubiquitin, which is currently the most sensitive marker of Lewy bodies and Lewy neurites. Staining for α-synuclein thus will replace staining for ubiquitin as the preferred method for detecting Lewy bodies and Lewy neurites. We have isolated Lewy body filaments by a method used for the extraction of paired helical filaments from Alzheimer’s disease brain. By immunoelectron microscopy, extracted filaments were labeled strongly by anti-α-synuclein antibodies. The morphologies of the 5- to 10-nm filaments and their staining characteristics suggest that extended α-synuclein molecules run parallel to the filament axis and that the filaments are polar structures. These findings indicate that α-synuclein forms the major filamentous component of Lewy bodies and Lewy neurites.

Coiled Bodies Preferentially Associate with U4, U11, and U12 Small Nuclear RNA Genes in Interphase HeLa Cells but Not with U6 and U7 Genes

Coiled bodies (CBs) are nuclear organelles involved in the metabolism of small nuclear RNAs (snRNAs) and histone messages. Their structural morphology and molecular composition have been conserved from plants to animals. CBs preferentially and specifically associate with genes that encode U1, U2, and U3 snRNAs as well as the cell cycle–regulated histone loci. A common link among these previously identified CB-associated genes is that they are either clustered or tandemly repeated in the human genome. In an effort to identify additional loci that associate with CBs, we have isolated and mapped the chromosomal locations of genomic clones corresponding to bona fide U4, U6, U7, U11, and U12 snRNA loci. Unlike the clustered U1 and U2 genes, each of these loci encode a single gene, with the exception of the U4 clone, which contains two genes. We next examined the association of these snRNA genes with CBs and found that they colocalized less frequently than their multicopy counterparts. To differentiate a lower level of preferential association from random colocalization, we developed a theoretical model of random colocalization, which yielded expected values for χ2 tests against the experimental data. Certain single-copy snRNA genes (U4, U11, and U12) but not controls were found to significantly (p < 0.000001) associate with CBs. Recent evidence indicates that the interactions between CBs and genes are mediated by nascent transcripts. Taken together, these new results suggest that CB association may be substantially augmented by the increased transcriptional capacity of clustered genes. Possible functional roles for the observed interactions of CBs with snRNA genes are discussed.

Polaris, a Protein Involved in Left-Right Axis Patterning, Localizes to Basal Bodies and Cilia

Mutations in Tg737 cause a wide spectrum of phenotypes, including random left-right axis specification, polycystic kidney disease, liver and pancreatic defects, hydrocephalus, and skeletal patterning abnormalities. To further assess the biological function of Tg737 and its role in the mutant pathology, we identified the cell population expressing Tg737 and determined the subcellular localization of its protein product called Polaris. Tg737 expression is associated with cells possessing either motile or immotile cilia and sperm. Similarly, Polaris concentrated just below the apical membrane in the region of the basal bodies and within the cilia or flagellar axoneme. The data suggest that Polaris functions in a ciliogenic pathway or in cilia maintenance, a role supported by the loss of cilia on the ependymal cell layer in ventricles of Tg737orpk brains and by the lack of node cilia in Tg737Δ2-3βGal mutants.

Cucumber Cotyledon Lipoxygenase during Postgerminative Growth. Its Expression and Action on Lipid Bodies

In cucumber (Cucumis sativus), high lipoxygenase-1 (LOX-1) activity has been detected in the soluble fraction prepared from cotyledons of germinating seeds, and the involvement of this enzyme in lipid turnover has been suggested (K. Matsui, M. Irie, T. Kajiwara, A. Hatanaka [1992] Plant Sci 85: 23–32; I. Fuessner, C. Wasternack, H. Kindl, H. Kühn [1995] Proc Natl Acad Sci USA 92: 11849–11853). In this study we have investigated the expression of the gene lox-1, corresponding to the LOX-1 enzyme. LOX-1 expression is highly coordinated with that of a typical glyoxysomal enzyme, isocitrate lyase, during the postgerminative stage of cotyledon development. In contrast, although icl transcripts accumulated in tissue during in vitro senescence, no accumulation of lox-1 mRNA could be observed, suggesting that lox-1 plays a specialized role in fat mobilization. LOX-1 is also known to be a major lipid body protein. The partial peptide sequences of purified LOX-1 and lipid body LOX-1 entirely coincided with that deduced from the lox-1 cDNA sequence. The data strongly suggest that LOX-1 and lipid body LOX-1 are derived from a single gene and that LOX-1 can exist both in the cytosol and on the lipid bodies. We constructed an in vitro oxygenation system to address the mechanism of this dual localization and to investigate the action of LOX-1 on lipids in the lipid bodies. LOX-1 cannot act on the lipids in intact lipid bodies, although degradation of lipid body proteins, either during seedling growth or by treatment with trypsin, allows lipid bodies to become susceptible to LOX-1. We discuss the role of LOX-1 in fat mobilization and its mechanism of action.

Horizontal transfer of oncogenes by uptake of apoptotic bodies

Tumor formation involves the accumulation of a series of genetic alterations that are required for malignant growth. In most malignancies, genetic changes can be observed at the chromosomal level as losses or gains of whole or large portions of chromosomes. Here we provide evidence that tumor DNA may be horizontally transferred by the uptake of apoptotic bodies. Phagocytosis of apoptotic bodies derived from H-rasV12- and human c-myc-transfected rat fibroblasts resulted in loss of contact inhibition in vitro and a tumorigenic phenotype in vivo. Fluorescence in situ hybridization analysis revealed the presence of rat chromosomes or of rat and mouse fusion chromosomes in the nuclei of the recipient murine cells. The transferred DNA was propagated, provided that the transferred DNA conferred a selective advantage to the cell and that the phagocytotic host cell was p53-negative. These results suggest that lateral transfer of DNA between eukaryotic cells may result in aneuploidy and the accumulation of genetic changes that are necessary for tumor formation.

Accumulation of Mutant Huntingtin Fragments in Aggresome-like Inclusion Bodies as a Result of Insufficient Protein Degradation

The huntingtin exon 1 proteins with a polyglutamine repeat in the pathological range (51 or 83 glutamines), but not with a polyglutamine tract in the normal range (20 glutamines), form aggresome-like perinuclear inclusions in human 293 Tet-Off cells. These structures contain aggregated, ubiquitinated huntingtin exon 1 protein with a characteristic fibrillar morphology. Inclusion bodies with truncated huntingtin protein are formed at centrosomes and are surrounded by vimentin filaments. Inhibition of proteasome activity resulted in a twofold increase in the amount of ubiquitinated, SDS-resistant aggregates, indicating that inclusion bodies accumulate when the capacity of the ubiquitin–proteasome system to degrade aggregation-prone huntingtin protein is exhausted. Immunofluorescence and electron microscopy with immunogold labeling revealed that the 20S, 19S, and 11S subunits of the 26S proteasome, the molecular chaperones BiP/GRP78, Hsp70, and Hsp40, as well as the RNA-binding protein TIA-1, the potential chaperone 14–3-3, and α-synuclein colocalize with the perinuclear inclusions. In 293 Tet-Off cells, inclusion body formation also resulted in cell toxicity and dramatic ultrastructural changes such as indentations and disruption of the nuclear envelope. Concentration of mitochondria around the inclusions and cytoplasmic vacuolation were also observed. Together these findings support the hypothesis that the ATP-dependent ubiquitin–proteasome system is a potential target for therapeutic interventions in glutamine repeat disorders.

Evidence for a Cytoskeleton-Associated Binding Site Involved in Prolamine mRNA Localization to the Protein Bodies in Rice Endosperm Tissue1

Previous studies have demonstrated that the mRNAs encoding the prolamine and glutelin storage proteins are localized to morphologically distinct membranes of the endoplasmic reticulum (ER) complex in developing rice (Oryza sativa L.) endosperm cells. To gain insight about this mRNA localization process, we investigated the association of prolamine polysomes on the ER that delimit the prolamine protein bodies (PBs). The bulk of the prolamine polysomes were resistant to extraction by 1% Triton X-100 either alone or together with puromycin, which suggests that these translation complexes are anchored to the PB surface through a second binding site in addition to the well-characterized ribosome-binding site of the ER-localized protein translocation complex. Suppression of translation initiation shows that these polysomes are bound through the mRNA, as shown by the simultaneous increase in the amounts of ribosome-free prolamine mRNAs and decrease in prolamine polysome content associated with the membrane-stripped PB fraction. The prolamine polysome-binding activity is likely to be associated with the cytoskeleton, based on the association of actin and tubulin with the prolamine polysomes and PBs after sucrose-density centrifugation.

Expression and analysis of presenilin 1 in a human neuronal system: localization in cell bodies and dendrites.

Mutations in the recently identified presenilin 1 gene on chromosome 14 cause early onset familial Alzheimer disease (FAD). Herein we describe the expression and analysis of the protein coded by presenilin 1 (PS1) in NT2N neurons, a human neuronal model system. PS1 was expressed using recombinant Semliki Forest virions and detected by introduced antigenic tags or antisera to PS1-derived peptides. Immunoprecipitation revealed two major PS1 bands of approximately 43 and 50 kDa, neither of which were N-glycosylated or O-glycosylated. Immunoreactive PS1 was detected in cell bodies and dendrites of NT2N neurons but not in axons or on the cell surface. PS1 was also detected in BHK cells, where it was also intracellular and colocalized with calnexin, a marker for the rough endoplasmic reticulum. A mutant form of PS1 linked to FAD did not differ from the wild-type protein at the light microscopic level. The model system described here will enable studies of the function of PS1 in human neurons and the role of mutant PS1 in FAD.

Coiled bodies contain U7 small nuclear RNA and associate with specific DNA sequences in interphase human cells.

Coiled bodies (CBs) are nuclear organelles whose structures appear to be highly conserved in evolution. In rapidly cycling cells, they are typically located in the nucleoplasm but are often found in contact with the nucleolus. The CBs in human cells contain a unique protein, called p80-coilin. Studies on amphibian oocyte nuclei have revealed a protein within the "sphere" organelle that shares significant structural similarity to p80-coilin. Spheres and CBs are also highly enriched in small nuclear ribonucleoproteins and other RNA-processing components. We present evidence that, like spheres, CBs contain U7 small nuclear RNA (snRNA) and associate with specific chromosomal loci. Using biotinylated 2'-O-methyl oligonucleotides complementary to the 5' end of U7 snRNA and fluorescence in situ hybridization, we show that U7 is distributed throughout the nucleoplasm, excluding nucleoli, and is concentrated in CBs. Interestingly, we found that CBs often associate with subsets of the histone, U1, and U2 snRNA gene loci in interphase HeLa-ATCC and HEp-2 monolayer cells. However, in a strain of suspension-grown HeLa cells, called HeLa-JS1000, we found a much lower rate of association between CBs and snRNA genes. Possible roles for CBs in the metabolism of these various histone and snRNAs are discussed.