Yasuko Hayashi

Suppression of aggregate formation and apoptosis by transglutaminase inhibitors in cells expressing truncated DRPLA protein with an expanded polyglutamine stretch

To elucidate the molecular mechanisms whereby expanded polyglutamine stretches elicit a gain of toxic function, we expressed full-length and truncated DRPLA (dentatorubral-pallidoluysian atrophy) cDNAs with or without expanded CAG repeats in COS-7 cells. We found that truncated DRPLA proteins containing an expanded polyglutamine stretch form filamentous peri- and intranuclear aggregates and undergo apoptosis. The apoptotic cell death was partially suppressed by the transglutaminase inhibitors cystamine and monodansyl cadaverine (but not putrescine), suggesting involvement of a transglutaminase reaction and providing a potential basis for the development of therapeutic measures for CAG-repeat expansion diseases.

An Endoplasmic Reticulum-Derived Structure That Is Induced under Stress Conditions in Arabidopsis

The endoplasmic reticulum (ER) body is a characteristic structure derived from ER and is referred to as a proteinase-sorting system that assists the plant cell under various stress conditions. Fluorescent ER bodies were observed in transgenic plants of Arabidopsis expressing green fluorescent protein fused with an ER retention signal. ER bodies were widely distributed in the epidermal cells of whole seedlings. In contrast, rosette leaves had no ER bodies. We found that wound stress induced the formation of many ER bodies in rosette leaves. ER bodies were also induced by treatment with methyl jasmonate (MeJA), a plant hormone involved in the defense against wounding and chewing by insects. The induction of ER bodies was suppressed by ethylene. An electron microscopic analysis showed that typical ER bodies were induced in the non-transgenic rosette leaves treated with MeJA. An experiment using coi1 and etr1-4 mutant plants showed that the induction of ER bodies was strictly coupled with the signal transduction of MeJA and ethylene. These results suggested that the formation of ER bodies is a novel and unique type of endomembrane system in the response of plant cells to environmental stresses. It is possible that the biological function of ER bodies is related to defense systems in higher plants.

Hereditary dentatorubral-pallidoluysian atrophy: detection of widespread ubiquitinated neuronal and glial intranuclear inclusions in the brain

Abstract We examined the brains and spinal cords of seven patients with clinicopathologically and genetically confirmed hereditary dentatorubral-pallidoluysian atrophy (DRPLA) using an antibody against ubiquitin, and found small, round immunoreactive intranuclear inclusions in both neurons and glial cells in various brain regions. Ubiquitinated neuronal intranuclear inclusions (uNIIs) were consistently found in the striatum, the pontine nuclei, the inferior olivary complex, the cerebellar cortex and the dentate nucleus. Ubiquitinated glial intranuclear inclusions (uGIIs) were found less frequently than uNIIs. Most of the inclusion-bearing nuclei were of an astrocytic nature. Immunostaining with an antibody against DRPLA protein revealed similar immunoreactive neuronal and glial intranuclear inclusions, but in much smaller in numbers compared with uNIIs and uGIIs. Electron microscopy showed that such inclusions were composed of granular and filamentous structures. These findings strongly suggest that, in DRPLA, the occurrence of uNIIs and uGIIs is directly related to the causative gene abnormality (an expanded CAG repeat encoding polyglutamine), that neurons are affected much more widely than previously recognized and that glial cells are also involved in the disease process.

Direct interaction between glyoxysomes and lipid bodies in cotyledons of theArabidopsis thaliana ped1 mutant

SummaryDuring germination and subsequent growth of fatty seeds, higher plants obtain energy from the glyconeogenic pathway in which fatty acids are converted to succinate in glyoxysomes, which contain enzymes for fatty acid β-oxidation and the glyoxylate cycle. TheArabidopsis thaliana ped1 gene encodes a 3-ketoacyl-CoA thiolase (EC 2.3.1.16) involved in fatty acid β-oxidation. Theped1 mutant shows normal germination and seedling growth under white light. However, etiolated cotyledons of theped1 mutant grow poorly in the dark and have small cotyledons. To elucidate the mechanisms of lipid degradation during germination in theped1 mutant, we examined the morphology of theped1 mutant. The glyoxysomes in etiolated cotyledons of theped1 mutant appeared abnormal, having tubular structures that contained many vesicles. Electron microscopic analysis revealed that the tubular structures in glyoxysomes are derived from invagination of the glyoxysomal membrane. By immunoelectron microscopic analysis, acyl-CoA synthetase (EC 6.2.1.3), which was located on the membrane of glyoxysomes in wild-type plants, was located on the membranes of the tubular structures in the glyoxysomes in theped1 mutant. These invagination sites were always in contact with lipid bodies. The tubular structure had many vesicles containing substances with the same electron density as those in the lipid bodies. From these results, we propose a model in which there is a direct mechanism of transporting lipids from the lipid bodies to glyoxysomes during fatty acid β-oxidation.

GNOM-LIKE1/ERMO1 and SEC24a/ERMO2 Are Required for Maintenance of Endoplasmic Reticulum Morphology in Arabidopsis thaliana

The endoplasmic reticulum (ER) is composed of tubules, sheets, and three-way junctions, resulting in a highly conserved polygonal network in all eukaryotes. The molecular mechanisms responsible for the organization of these structures are obscure. To identify novel factors responsible for ER morphology, we employed a forward genetic approach using a transgenic Arabidopsis thaliana plant (GFP-h) with fluorescently labeled ER. We isolated two mutants with defects in ER morphology and designated them endoplasmic reticulum morphology1 (ermo1) and ermo2. The cells of both mutants developed a number of ER-derived spherical bodies, ∼1 μm in diameter, in addition to the typical polygonal network of ER. The spherical bodies were distributed throughout the ermo1 cells, while they formed a large aggregate in ermo2 cells. We identified the responsible gene for ermo1 to be GNOM-LIKE1 (GNL1) and the gene for ermo2 to be SEC24a. Homologs of both GNL1 and SEC24a are involved in membrane trafficking between the ER and Golgi in yeast and animal cells. Our findings, however, suggest that GNL1/ERMO1 and SEC24a/ERMO2 have a novel function in ER morphology in higher plants.

Linkage mapping of the gene for Charcot-Marie-Tooth disease type 2 to chromosome 1p (CMT2A) and the clinical features of CMT2A

Charcot-Marie-Tooth disease type 2 (CMT2) is characterized by a motor conduction velocity of the median nerve of >38 m/sec and is a genetically heterogeneous disorder with at least three loci identified: CMT2A (1p35-36), CMT2B (3q13-22), CMT2C (not linked to any known loci), and CMT2D (7p14). In this study, we performed linkage analysis of two Japanese CMT2 families using markers flanking the CMT2A, CMT2B, and CMT2D loci. The highest cumulative multipoint lod score of 3.69 was obtained at D1S244. The CMT2B and CMT2D loci were excluded by the results of linkage analysis performed using markers D3S1551, D3S1290, and D7S484. The clinical features of the CMT2A affecting the two families include similar levels of muscle weakness of the posterior and anterior tibial muscles, tendon reflexes preserved in upper extremities but reduced or absent in lower extremities, no enlargement of the peripheral nerves, and mild sensory disturbance in only 20% of affected individuals.

Molecular characterization of an Arabidopsis acyl-coenzyme a synthetase localized on glyoxysomal membranes

In higher plants, fat-storing seeds utilize storage lipids as a source of energy during germination. To enter the β-oxidation pathway, fatty acids need to be activated to acyl-coenzyme As (CoAs) by the enzyme acyl-CoA synthetase (ACS; EC 6.2.1.3). Here, we report the characterization of an Arabidopsis cDNA clone encoding for a glyoxysomal acyl-CoA synthetase designatedAtLACS6. The cDNA sequence is 2,106 bp long and it encodes a polypeptide of 701 amino acids with a calculated molecular mass of 76,617 D. Analysis of the amino-terminal sequence indicates that acyl-CoA synthetase is synthesized as a larger precursor containing a cleavable amino-terminal presequence so that the mature polypeptide size is 663 amino acids. The presequence shows high similarity to the typical PTS2 (peroxisomal targeting signal 2). TheAtLACS6 also shows high amino acid identity to prokaryotic and eukaryotic fatty acyl-CoA synthetases. Immunocytochemical and cell fractionation analyses indicated that theAtLACS6 is localized on glyoxysomal membranes.AtLACS6 was overexpressed in insect cells and purified to near homogeneity. The purified enzyme is particularly active on long-chain fatty acids (C16:0). Results from immunoblot analysis revealed that the expression of both AtLACS6 and β-oxidation enzymes coincide with fatty acid degradation. These data suggested that AtLACS6 might play a regulatory role both in fatty acid import into glyoxysomes by making a complex with other factors, e.g. PMP70, and in fatty acid β-oxidation activating the fatty acids.

Hereditary dentatorubral-pallidoluysian atrophy: ubiquitinated filamentous inclusions in the cerebellar dentate nucleus neurons

Abstract We examined the cerebellar dentate nucleus (CDN) in 16 patients with hereditary dentatorubral-pallidoluysian atrophy (DRPLA), one of the neurodegenerative diseases caused by expansion of a CAG repeat encoding a polyglutamine tract in the disease protein. In all patients, some CDN neurons were found to contain ubiquitinated filamentous inclusions in their cytoplasm. On hematoxylin and eosin preparations, these filamentous inclusions were eosinophilic, basophilic or amphophilic, and were often found in areas of pale cytoplasm. Electron microscopy revealed that they consisted of bundles of filaments that were somewhat thicker than neurofilaments. These features of the present inclusions were indistinguishable from those of skein-like inclusions (SLI) previously described in the lower motor neurons in sporadic amyotrophic lateral sclerosis. We conclude that SLI can also occur in the CDN in DRPLA and believe that they reflect a characteristic pathological process in this disease.

Peroxisomal targeting signals in green algae

Peroxisomal enzymatic proteins contain targeting signals (PTS) to enable their import into peroxisomes. These targeting signals have been identified as PTS1 and PTS2 in mammalian, yeast, and higher plant cells; however, no PTS2-like amino acid sequences have been observed in enzymes from the genome database of Cyanidiochyzon merolae (Bangiophyceae), a primitive red algae. In studies on the evolution of PTS, it is important to know when their sequences came to be the peroxisomal targeting signals for all living organisms. To this end, we identified a number of genes in the genome database of the green algae Chlamydomonas reinhardtii, which contains amino acid sequences similar to those found in plant PTS. In order to determine whether these sequences function as PTS in green algae, we expressed modified green fluorescent proteins (GFP) fused to these putative PTS peptides under the cauliflower mosaic virus 35S promoter. To confirm whether granular structures containing GFP–PTS fusion proteins accumulated in the peroxisomes of Closterium ehrenbergii, we observed these cells after the peroxisomes were stained with 3, 3′-diaminobenzidine. Our results confirm that the GFP–PTS fusion proteins indeed accumulated in the peroxisomes of these green algae. These findings suggest that the peroxisomal transport system for PTS1 and PTS2 is conserved in green algal cells and that our fusion proteins can be used to visualize peroxisomes in live cells.

Vacuoles and Storage Organelles

The vacuole, a membrane-bound water-filled organelle which contains inorganic ions and organic compounds, is the most prominent organelle in plant cells. The vacuolar membrane, called the tonoplast, contains transport proteins that maintain cytoplasm homeostasis, including proton pumps which stabilize cytoplasmic pH, aquaporins which control water permeability, and ion transporters. The size and number of vacuoles varies greatly depending on cell type and stage of plant development. Mature plant cells generally contain one central or several very large vacuoles. By storing various materials, the central vacuole keeps its water potential as low as that of the cytoplasm, and maintains turgor pressure against the cell wall, which is essential in supporting plants in an upright position. Plant vacuoles also play roles in molecular degradation and storage to maintain a balance between biogenesis and degradation of substances and cell structures. In some specialized cells, vacuoles serve as mediators. In protein-seeds, vacuoles store proteins as protein bodies to be used in germination. In oil-seeds, lipids stored in oil bodies are transported in peroxisomes (glyoxysomes) and metabolized to produce energy for germination.