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Biomedical subjects

M Okabe

Publications and source records attributed to M Okabe.

At least 181 records · Page 10Linked to original sources
PubMed1997

Significance of alpha-fragment of metallothionein in cadmium binding.

In order to evaluate the significance of alpha- and beta-fragments of metallothionein with regard to Cd binding in biosynthetic processes, the Cd-binding ability of four mutant metallothioneins was examined using the Escherichia coli expression system. The features of the mutant metallothioneins were proteins in which cysteine residues in the alpha- or beta-fragment were replaced with alanine residues, or that the sequential order of the fragments was altered. The expressed mutant metallothioneins having an intact alpha-fragment showed the constructive abilities of the Cd-thiolate cluster. On the other hand, mutant metallothionein having an alpha-fragment lacking metal-binding sites exhibited no Cd-binding ability. The condition for maintaining the Cd-binding capability of metallothionein was that the alpha-fragment remains intact irrespective of the sequential order of the two fragments. The alpha-fragment is an indispensable component in metal-binding processes of Cd-metallothionein.

Amino Acid Sequence↗
PubMed1997

Cessation of spermatogenesis in juvenile spermatogonial depletion (jsd/jsd) mice.

BACKGROUND: Mice homozygous for the jsd (juvenile spermatogonial depletion) allele are sterile because they become azoospermic. The onset of such azoospermia was investigated by histologic analysis of sections of testes from jsd/jsd mice. METHOD: The testes removed from C57BL/6-jsd/jsd mice aged 3 to 10 weeks were examined microscopically. RESULTS: At 3 weeks of age, spermatocytes were seen in most of the seminiferous tubules of jsd/jsd mice. However, the number of tubules that contained spermatids was significantly smaller than that counted in the wild-type mice. Since degenerative figures were not abundant in the jsd/jsd testes, the decreased number of spermatids found in the tubules suggested a longer duration of development from spermatocyte to spermatid in jsd/jsd mice. The abnormality extended to the development of type B spermatogonia, and a decrease in their number became apparent after 6 weeks of age in most of the jsd/jsd tubules. However, as early as 3 weeks of age, a few seminiferous tubules in jsd/jsd mice already contained only Sertoli cells and type A spermatogonia. CONCLUSION: It is assumed that the decrease in type B spermatogonia occurred at various ages and locations. The defect of spermatogenesis in jsd/jsd mice was attributable to aberrations in multiple steps of spermatogenesis.

Aging↗
PubMed1997

Osmolarity in renal medulla of transgenic mice regulates transcription via 5'-flanking region of canine BGT1 gene.

Betaine is a major compatible osmolyte accumulated in the mammalian kidney medulla and in Madin-Darby canine kidney cells in response to hypertonicity. The accumulation is the result of an increase in maximal velocity of the Na(+)- and Cl-coupled betaine transporter designated BGT1. We have previously cloned the canine BGT1 gene and identified a tonicity-responsive enhancer element (TonE) in its 5'-flanking region. Here we report studies of transgenic mice that have in their genome 2.4 kb of the 5'-flanking region of the canine BGT1 gene in front of a chloramphenicol acetyl-transferase (CAT) reporter. Expression of CAT mRNA was detected only in the renal medulla and was increased by experimental manipulations that increase the tonicity of the renal medulla and decreased by manipulations that decrease medullary tonicity. We conclude that the 2.4-kb 5'-flanking region of the BGT1 gene mediates an increase in transcription in response to hyperosmolarity in the renal medulla.

Animals↗
PubMed1997

Intrinsic and extrinsic determinants regulating cell fate decision in developing nervous system.

Cell fate in the nervous system is determined by environmental signals and/or heredity. They can be referred to as extrinsic and intrinsic determinants, respectively. The molecular and cellular mechanisms underlying these processes are well conserved from invertebrates to vertebrates. We have identified both types of determinants through the intensive screening of P-element-induced Drosophila mutants affected in neural development. As a member of the first category, argos gene product which regulates cell-cell interaction in the developing nervous system gives a good example. As a member of the second category, we refer to Drosophila musashi gene encoding a neural RNA-binding protein. The fractions of these gene products and application to the mammalian nervous system will be discussed.

Animals↗
PubMed1997

Three-dimensional spiral computed tomography angiography as an alternative imaging modality for a silent dissecting aortic aneurysm--a case report.

The authors report a patient with silent dissecting aortic aneurysm in whom three-dimensional spiral computed tomography (CT) angiography (3D-CTA) provided important imaging data. Images obtained by 3D-CTA were compared with the results of both conventional angiography and CT. They conclude that 3D-CTA was a powerful diagnostic modality for this patient, in addition to conventional CT and angiography.

Aortic Dissection↗
PubMed1997

Copper-metallothionein in the kidney of macular mice: a model for Menkes disease.

Menkes disease is an X-linked disorder of copper metabolism. Excess amounts of copper in the kidney of Macular mice, a model for this disease, were found as copper-metallothionein (Cu-MT) from kidney of the mice. Histochemical studies of Cu-MT based on its autofluorescent emission properties showed that the protein was predominant in the proximal convoluted tubule (PCT) cells of the cortex. PCT cells are known to be the primary site of the nephrotoxicity caused by heavy metals. MT mRNA was also observed in the cortex, indicating that the protein was biosynthesized in this region. On the basis of these results, we suggest that biosynthesis and degradation of Cu-MT occur repeatedly in the PCT cells of the cortex. We also compared the histochemical localization of Cu-MT in Macular mice and Long-Evans cinnamon rats, a model for Wilson's disease. The significance of this comparison is discussed.

Acid Phosphatase↗
PubMed1997

Two-step induction of chordotonal organ precursors in Drosophila embryogenesis.

The chordotonal (Ch) organ, an internal stretch receptor located in the subepidermal layer, is one of the major sensory organs in the peripheral nervous system of Drosophila melanogaster. Although the cell lineage of the Ch organ has been well characterized in many studies, the determination machinery of Ch organ precursor cells (COPs) remains largely unresolved. Here we report that the rhomboid (rho) gene and the activity of the Drosophila EGF receptor (DER) signaling pathway are necessary to induce specifically three of the eight COPs in an embryonic abdominal hemisegment. The cell-lineage analysis of COPs using the yeast flpase (flp/FRT) method indicated that each of the eight COPs originated from an individual undifferentiated ectodermal cell. The eight COPs in each abdominal hemisegment seemed to be determined by a two-phase induction: first, five COPs are determined by the action of the proneural gene atonal and neurogenic genes. Subsequently, these five COPs start to express the rho gene, and rho activates the DER-signaling pathway in neighboring cells and induces argos expression. Three of these argos-expressing cells differentiate into the three remaining COPs and they prevent neighboring cells from becoming extra COPs.

Animals↗
PubMed1997

Right bundle block in a patient with acute posterior myocardial infarction.

We present here a patient with the unusual combination of a newly developed right bundle branch block (RBBB) and an acute posterior myocardial infarction (MI). A dissecting MI with interventricular septal (IVS) rupture was initially thought to have caused RBBB. However, histologic examination revealed that the right bundle branch (RBB) had no ischemic involvement, but did show fibrosis, which suggests that this chronic damage of the RBB was a major contributor to the development of RBBB. This case confirms that the RBB is rarely involved by a posterior MI even in the presence of a dissecting IVS rupture.

Acute Disease↗
PubMed1997

Platelet-derived growth factor blocks the cell-cycle transition from the G0 to G1 phase in subcultured angiogenic endothelial cells in rat thoracic aorta.

Platelet-derived growth factor (PDGF)-BB induces tube formation by the differentiating (tube-forming) endothelial cells (EC) of rat thoracic aorta, although PDGF-BB does not affect the proliferative EC (increasing the cell numbers) at the progression phase. These changes in the responses to PDGF-BB were due to the phenotype-dependent expression of PDGF beta-receptor (PDGFR-beta) on EC because PDGFR-beta-like immunoreactivity was observed in the angiogenic EC forming a tube-like structure in 35-day culture with 10% fetal bovine serum, but not in the proliferative EC in 5-day culture. To elucidate the functional role of PDGFR-beta in the alteration of EC phenotype, the influence of PDGF-BB on the cell cycle of EC was investigated by flow cytometry. This analysis demonstrates that PDGF-BB blocks the transition from the G0 to G1 phase in the 35-day cultured EC, although no effect was observed on any phases of the cell cycle in 5-day culture. We conclude that 1) PDGFR-beta is expressed in mature angiogenic EC of rat aorta, and 2) PDGF-BB may contribute to promotion of the EC differentiation with tubular morphogenesis by inhibiting cell growth.

Animals↗
PubMed1997

Effect of ferrous ion on amino acid metabolism in mildiomycin production by Streptoverticillium rimofaciens.

The physiological features of the mildiomycin production by Streptoverticillium rimofaciens were examined in iron-sufficient and -deficient media. Activities of NADP-linked glutamate dehydrogenase (GDH) and aspartate aminotransferase (AAT) were markedly enhanced by the addition of 10 micrograms/ml of ferrous ion into culture. Ammonium nitrogen assimilation increased with the increase in mildiomycin production. These indicate that ferrous ion contributes the supply of amino acids as a precursor of mildiomycin production. In the iron-sufficient medium, glutamate, aspartate, serine and arginine in cells were 2 to 10-fold to those in the iron-deficient medium. The major amino acid excreted from cells was arginine in the iron-sufficient culture, while in the iron-deficient culture, valine. Change in the amino acid profile by addition of ferrous ion was useful for mildiomycin biosynthesis, in which ferrous ion played a leading role in amino acid metabolism.

Alanine Dehydrogenase↗
PubMed1997

Evolutionarily conserved mechanisms regulating neural development: lessons from the development of Drosophila peripheral nervous systems.

Functions of genes regulating the development of Drosophila peripheral nervous systems are summarized herein. These genes can be classified into 6 groups: <1> prepattern genes, <2> proneural genes, <3> neurogenic genes, <4> neuronal precursor genes, <5> neuronal precursor type selector genes, and <6> cell-division and lineage genes. The mechanisms described herein provide excellent paradigms in the regulation of the development of other tissues in Drosophila, as well as in other organisms, including vertebrates. The roles of two different inhibitory mechanisms, i.e. Notch-signaling and Argos, in the development of Drosophila neural precursor cells are also discussed.

Animals↗
PubMed1997

Effect of ferrous ion on amino acid metabolism in mildiomycin production by Streptoverticillium rimofaciens

The physiological features of the mildiomycin production by Streptoverticillium rimofaciens were examined in iron-sufficient and -deficient media. Activities of NADP-linked glutamate dehydrogenase (GDH) and aspartate aminotransferase (AAT) were markedly enhanced by the addition of 10 micrograms/ml of ferrous ion into culture. Ammonium nitrogen assimilation increased with the increase in mildiomycin production. These indicate that ferrous ion contributes the supply of amino acids as a precursor of mildiomycin production. In the iron-sufficient medium, glutamate, aspartate, serine and arginine in cells were 2 to 10-fold to those in the iron-deficient medium. The major amino acid excreted from cells was arginine in the iron-sufficient culture, while in the iron-deficient culture, valine. Change in the amino acid profile by addition of ferrous ion was useful for mildiomycin biosynthesis, in which ferrous ion played a leading role in amino acid metabolism.

Journal Article↗
PubMed1996

Neurochemical and histochemical evidence for an abnormal catecholamine metabolism in the cerebral cortex of the Long-Evans Cinnamon rat before excessive copper accumulation in the brain.

Distributions of norepinephrine (NE), dopamine (DA) and its metabolites in the cerebral cortex in Long-Evans Cinnamon (LEC) rats, an animal model of Wilson's disease, aged 4, 10 (in the early stage of the disease) and 20 weeks (in the advanced stage of the disease) were determined to elucidate the effect of the abnormal copper (Cu) metabolism observed in the LEC rat on the brain catecholamine metabolism. NE depression as well as excessive accumulations of DA and facilitation of the DA catabolic pathway to its acidic metabolites were observed in the cerebral cortex of the LEC rat at 4 and 10 weeks of age. Furthermore, immunohistochemical analysis of the cuproenzyme dopamine-beta-hydroxylase (DBH) showed lower antigenicity of DBH in the cortical neurons in the cerebral cortex of LEC rats aged 4 weeks than in control rats. These results suggest that neurochemical disturbances involved in an abnormal catecholamine metabolism may occur in the cerebral cortex of the LEC rat before excessive Cu accumulation.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1996

The Drosophila secreted protein Argos regulates signal transduction in the Ras/MAPK pathway.

The Drosophila argos gene encodes a secreted protein with an EGF motif which acts as an inhibitor of cellular differentiation in multiple developmental processes. To investigate the cellular pathways regulated by Argos, we screened for mutations which could modify the phenotype caused by overexpression of argos. We show that the effects of argos overexpression on the eye and wing vein development are suppressed by gain-of-function mutations of the MAPKK/D-MEK gene (Dsor1/D-mek) and the MAPK/ERK-A gene (rolled) and were enhanced by loss-of-function mutations of Star. Loss-of-function mutations in components of the Ras/MAPK signaling cascade act as dominant suppressors of the phenotype caused by the argos null mutations. A loss-of-function argos mutation enhanced the overproduction of R7 neurons caused by gain-of-function alleles of Son of sevenless and Dsor1. Conversely, overexpression of argos inhibited formation of the extra R7 cells that was caused by high-level MAPK/ERK-A activity. A phenotype of the sev; argos double mutants revealed that sev is epistatic to argos. These results provide evidence that Argos negatively regulates signal transduction events in the Ras/MAPK cascade.

Animals↗
PubMed1996

Neoplastic transformation of normal hematopoietic cells by constitutively activating mutations of c-kit receptor tyrosine kinase.

The c-kit proto-oncogene encodes a receptor tyrosine kinase that is crucial to hematopoiesis, melanogenesis, and gametogeneis. Although the enzymatic activity of the c-kit product (KIT) is regulated by its ligand, both the Val559-->Gly (G559) mutation in the juxtamembrane domain and the Asp814-->Val (V814) mutation in the phosphotransferase domain lead to constitutive activation of KIT. By retroviral infection of hematopoietic progenitor cells with KIT(G559) or KIT(V814), KIT(G559) induced development of granulocyte/macrophage and mast-cell colonies in vitro without the addition of exogenous growth factors. KIT(V814) induced factor-independent growth of various types of hematopoietic progenitor cells, resulting in the development of mixed erythroid/myeloid colonies in addition to granulocyte/macrophage and mast-cell colonies. Furthermore, transplantation of KIT(G559) and KIT(V814)-infected bone marrow cells led to development of acute leukemia in one of 10 and six of 10 transplanted mice, respectively. No mice developed hematologic malignancies after transplantation of wild-type KIT-infected cells. Furthermore, transgenic mice expressing KIT(V814) developed acute leukemia or malignant lymphoma. These results demonstrate a direct role of the mutant KITs, particularly KIT(V814), in tumorigenesis of hematopoietic cells and suggest that similar mutations may contribute to the development of human hematologic malignancies.

Animals↗
PubMed1996

Mouse-Musashi-1, a neural RNA-binding protein highly enriched in the mammalian CNS stem cell.

There is increasing interest in the role of RNA-binding proteins during neural development. Drosophila Musashi is one of the neural RNA-binding proteins essential for neural development and required for asymmetric cell divisions in the Drosophila adult sensory organ development. Here, a novel mammalian neural RNA-binding protein, mouse-Musashi-1, was identified based on the homology to Drosophila Musashi and Xenopus NRP-1. In the developing CNS, mouse-Musashi-1 protein was highly enriched in the CNS stem cell. Single-cell culture experiments indicated that mouse-Musashi-1 expression is associated with neural precursor cells that are capable of generating neurons and glia. In contrast, in fully differentiated neuronal and glial cells mouse-Musashi-1 expression is lost. This expression pattern of mouse-Musashi-1 is complementary to that of another mammalian neural RNA-binding protein, Hu (a mammalian homologue of a Drosophila neuronal RNA-binding protein Elav), that is expressed in postmitotic neurons within the CNS. In vitro studies indicated that mouse-Musashi-1 possesses binding preferences on poly(G) RNA homopolymer, whereas Hu is known to preferentially bind to short A/U-rich regions in RNA. Based on their differential expression patterns and distinct preferential target RNA sequences, we believe that the mouse-Musashi-1 and Hu proteins may play distinct roles in neurogenesis, either through sequential regulatory mechanisms or differential sorting of mRNA populations during asymmetric division of neural precursor cells.

Amino Acid Sequence↗
PubMed1996

Glycosylphosphatidylinositol-anchor-deficient mice: implications for clonal dominance of mutant cells in paroxysmal nocturnal hemoglobinuria.

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired hematopoietic stem cell disorder characterized by complement-mediated hemolysis. Abnormal hematopoietic cells from patients with PNH are deficient in glycosylphosphatidylinositol (GPI)-anchored proteins and clonally dominate various hematopoietic lineages in the bone marrow and the peripheral blood. Analysis of many patients with PNH has showed that somatic mutation in the X-linked gene PIG-A is responsible for the GPI-anchor deficiency in PNH. The PIG-A mutation must also be relevant to the clonal dominance of GPI-anchor deficient (GPI-) blood cells because two or more PIG-A mutant clones become dominant in many patients. However, whether the PIG-A mutation alone is sufficient for clonal dominance is not known. To address this question, we generated chimeric mice using Pig-a (the murine homologue of PIG-A) disrupted embryonic stem (ES) cells, in which the animals are chimeric with respect to the surface expression of GPI-anchored proteins. The chimerism of hematopoietic and nonhematopoietic tissues in such mice was always low, suggesting that the higher contribution of Pig-a disrupted GPI- cells had a lethal effect on the chimera. GPI- cells appeared in the peripheral blood of some of the chimeric mice. However, the percentage of GPI- erythrocytes did not increase for 10 months after birth, implying that the Pig-a mutation alone does not immediately cause the clonal dominance of GPI- blood cells; another pathologic or physiologic change(s) in the hematopoietic environments or in the clone itself may be necessary.

Animals↗
PubMed1996

The function of the Drosophila argos gene product in the development of embryonic chordotonal organs.

We characterized the embryonic expression pattern and mutant phenotypes of the Drosophila gene argos, which encodes a secreted protein with an epidermal growth factor motif. The argos null mutation caused an increase in chordotonal (Ch) organs in both the thoracic and the abdominal segments, whereas overexpression of the argos gene resulted in a decrease in these organs. We showed that the argos transcripts are expressed transiently in the cells surrounding the Ch organ precursor and that the gene rhomboid (rho), which is involved in the regulation of the number of Ch organs, acts epistatically to argos in this event. Our findings suggest that argos plays a role in Ch organ precursor formation and regulates the final number of Ch organs.

Abdomen↗