Biomedical subjects

Katsumi Higashi

Publications and source records attributed to Katsumi Higashi.

13 recordsLinked to original sources

PubMed2006

Continuous recognition of the elicitor signal for several hours is prerequisite for induction of cell death and prolonged activation of signaling events in tobacco BY-2 cells.

To provide insights into the mechanisms by which receptors for pathogenic elicitors activate defense signaling, we investigated the duration of cryptogein treatment required for induction of various defense responses including programmed cell death in synchronized tobacco BY-2 cells. Transient cryptogein treatment induced only a rapid and transient phase of oxidative burst and mitogen-activated protein kinase (MAPK) activation. Prolonged production of *O(2)(-) and prolonged activation of MAPKs, as well as accumulation of transcripts of defense-related genes and cell death, required continuous recognition of cryptogein for several hours. In contrast, desensitization was gradually induced in the absence of the elicitor.

Algal Proteins↗

PubMed2005

Abscisic acid and stress treatment are essential for the acquisition of embryogenic competence by carrot somatic cells.

Studies of carrot embryogenesis have suggested that abscisic acid (ABA) is involved in somatic embryogenesis. A relationship between endogenous ABA and the induction of somatic embryogenesis was demonstrated using stress-induced system of somatic embryos. The embryonic-specific genes C-ABI3 and embryogenic cell proteins (ECPs) were expressed during stress treatment prior to the formation of somatic embryos. The stress-induction system for embryogenesis was clearly distinguished by two phases: the acquisition of embryogenic competence and the formation of a somatic embryo. Somatic embryo formation was inhibited by the application of fluridone (especially at 10(-4) M), a potent inhibitor of ABA biosynthesis, during stress treatment. The inhibitory effect of fluridone was nullified by the simultaneous application of fluridone and ABA. The level of endogenous ABA increased transiently during stress. However, somatic embryogenesis was not significantly induced by the application of only ABA to the endogenous level, in the absence of stress. These results suggest that the induction of somatic embryogenesis, in particular the acquisition of embryogenic competence, is caused not only by the presence of ABA but also by physiological responses that are directly controlled by stresses.

Abscisic Acid↗

PubMed2005

Cell cycle dependence of elicitor-induced signal transduction in tobacco BY-2 cells.

The molecular links between the cell cycle and defense responses in plants are largely unknown. Using synchronized tobacco BY-2 cells, we analyzed the cell cycle dependence of elicitor-induced defense responses. In synchronized cultured apoaequorin-expressing cells, the increase in cytosolic free Ca2+ induced by a proteinaceous elicitor, cryptogein, was greatly suppressed during the G2 and M phases in comparison with G1 or S phases. Treatment with cryptogein during the G1 or S phases also induced biphasic (rapid/transient and slow/prolonged) responses in activation of mitogen-activated protein kinases (MAPKs) and production of reactive oxygen species (ROS). In contrast, elicitor treatment during the G2 or M phases induced only a rapid and transient phase of MAPK activation and ROS production. Their slow and prolonged phases as well as expression of defense-related genes, cell cycle arrest and cell death were induced only after the cell cycle progressed to the G1 phase; removal of the elicitor before the start of the G1 phase inhibited these responses. These results suggest that although cryptogein recognition occurred at all phases of the cell cycle, the recognition during the S or G1 phases, but not at the G2 or M phases, induces the prolonged activation of MAPKs and the prolonged production of ROS, followed by cell cycle arrest, accumulation of defense-related gene transcripts and cell death. Elicitor signal transduction depends on the cell cycle and is regulated differently at each phase.

Aequorin↗

PubMed2004

Identification of putative voltage-dependent Ca2+-permeable channels involved in cryptogein-induced Ca2+ transients and defense responses in tobacco BY-2 cells.

Ca(2+) is the pivotal second messenger for induction of defense responses induced by treatment of pathogen-derived elicitor or microbial infection in plants. However, molecular bases for elicitor-induced generation of Ca(2+) signals (Ca(2+) transients) are largely unknown. We here identified cDNAs for putative voltage-dependent Ca(2+)-permeable channels, NtTPC1A and NtTPC1B, that are homologous to TPC1 (two pore channel) from suspension-cultured tobacco BY-2 cells. NtTPC1s complemented the growth of a Saccharomyces cerevisiae mutant defective in CCH1, a putative Ca(2+) channel, in a low Ca(2+) medium, suggesting that both products permeate Ca(2+) through the plasma membrane. Cosuppression of NtTPC1s in apoaequorin-expressing BY-2 cells resulted in inhibition of rise in cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) in response to sucrose and a fungal elicitor cryptogein, while it did not affect hypoosmotic shock-induced [Ca(2+)](cyt) increase. Cosuppression of NtTPC1s also caused suppression of cryptogein-induced programmed cell death and defense-related gene expression. These results suggest that NtTPC1s are involved in Ca(2+) mobilization induced by the cryptogein and sucrose, and have crucial roles in cryptogein-induced signal transduction pathway.

Algal Proteins↗

PubMed2004

Cryptogein-induced initial events in tobacco BY-2 cells: pharmacological characterization of molecular relationship among cytosolic Ca(2+) transients, anion efflux and production of reactive oxygen species.

Ion fluxes and the production of reactive oxygen species (ROS) are early events that follow elicitor treatment or microbial infection. However, molecular mechanisms for these responses as well as their relationship have been controversial and still largely unknown. We here simultaneously monitored the temporal sequence of initial events at the plasma membrane in suspension-cultured tobacco cells (cell line BY-2) in response to a purified proteinaceous elicitor, cryptogein, which induced hypersensitive cell death. The elicitor induced transient rise in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) showing two distinct peaks, followed by biphasic (rapid/transient and slow/prolonged) Cl(-) efflux and H(+) influx. Pharmacological analyses suggested that the two phases of the [Ca(2+)](cyt) response correspond to Ca(2+) influx through the plasma membrane and an inositol 1,4,5-trisphophate-mediated release of Ca(2+) from intracellular Ca(2+) stores, respectively, and the [Ca(2+)](cyt) transients and the Cl(-) efflux were mutually dependent events regulated by protein phosphorylation. The elicitor also induced production of ROS including (*)O(2)(-) and H(2)O(2), which initiated after the [Ca(2+)](cyt) rise and required Ca(2+) influx, Cl(-) efflux and protein phosphorylation. An inhibitor of NADPH oxidase, diphenylene iodonium, completely inhibited the elicitor-induced production of (*)O(2)(-) and H(2)O(2), but did not affect the [Ca(2+)](cyt) transients. These results suggest that cryptogein-induced plasma membrane Ca(2+) influx is independent of ROS, and NADPH oxidase dependent ROS production is regulated by these series of ion fluxes.

Algal Proteins↗

PubMed2004

Frequency distribution of thiopurine S-methyltransferase activity in red blood cells of a healthy Japanese population.

Thiopurine S-methyltransferase (TPMT), which exhibits a genetic polymorphism, plays an important role in the metabolism of thiopurine drugs such as mercaptopurine, thioguanine, and azathioprine. To determine the frequency distribution of TPMT activity in 157 Japanese subjects with different TPMT genotypes, ie, TPMT*1/*1 and TPMT*1/*3, the authors measured levels of 6-methylmercaptopurine formed from 6-mercaptopurine in red blood cells lysates by HPLC. The TPMT activities in our Japanese subjects ranged from 11.0 to 42.6 pmol/h/mgHb. Although the mean value of TPMT activities in 6 subjects with TPMT*1/*3C (20.3 +/- 8.1 pmol/h/mgHb) was 25% lower than that in 151 subjects with TPMT*1/*1 (27.0 +/- 5.1 pmol/h/mgHb), there was overlap. The ranges of TPMT activity in subjects with TPMT*1/*1 and those with TPMT*1/*3C were similar. The median values in TPMT*1/*3C and TPMT*1/*1 individuals were 20.1 (11.0-31.2) and 26.8 pmol/h/mgHb (15.7-42.7), respectively (Mann-Whitney U-test: median difference 6.7 pmol/h/mgHb, 95% CI 0-25.5, P < 0.05). This observation may have relevance for the use of 6-mercaptopurine and azathioprine as therapeutic agents in Japanese patients.

Asian People↗

PubMed2004

Crosstalk between elicitor-induced cell death and cell cycle regulation in tobacco BY-2 cells.

The molecular links between cell cycle control and the regulation of programmed cell death are largely unknown in plants. Here we studied the relationship between the cell cycle and elicitor-induced cell death using synchronized tobacco BY-2 cells. Flow cytometry and fluorescence microscopy of nuclear DNA, and RNA gel-blot analyses of cell cycle-related genes revealed that the proteinaceous elicitor cryptogein induced cell cycle arrest at the G1 or G2 phase before the induction of cell death. Furthermore, the patterns of cell death induction and defence-related genes were different in different phases of the cell cycle. Constitutive treatment with cryptogein induced cell cycle arrest and cell death at the G1 or G2 phase. With transient treatment for 2 h, cell cycle arrest and cell death were only induced by treatment with the elicitor during the S or G1 phase. By contrast, the elicitor-induced production of reactive oxygen species was observed during all phases of the cell cycle. These results indicate that although recognition of the elicitor signal is cell cycle-independent, the induction of cell cycle arrest and cell death depends on the phase of the cell cycle.

Aphidicolin↗

PubMed2004

[Reticulocyte].

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Anemia↗

PubMed2003

4-Hydroxybenzyl alcohol accumulates in flowers and developing fruits of carrot and inhibits seed formation.

Somatic embryogenesis in carrot (Daucus carota) is autonomously inhibited by 4-hydroxybenzyl alcohol (4HBA), which is produced by embryogenic cells. Because somatic embryogenesis is used as a model of zygotic embryogenesis, we assayed for 4HBA in carrot seeds and analyzed the effect of 4HBA on seed formation to determine whether 4HBA is also produced during zygotic embryogenesis. HPLC analysis showed that 4HBA accumulated in flowers and immature and mature fruits, but not in vegetative tissues. The concentration of 4HBA was highest after flowering, when the zygote developed into the early globular-stage embryo. 4HBA accumulation then decreased with seed development. Exogenous application of 4HBA to immature carrot fruits inhibited seed formation. Many 4HBA-treated seeds did not include a mature embryo. These results indicate that the production and accumulation of 4HBA occurs during carrot seed development and that 4HBA has an inhibitory effect on carrot seed formation.

Benzyl Alcohols↗

PubMed2003

Ethylene advances the transition from vegetative growth to flowering in Arabidopsis thaliana.

The transition from vegetative growth to flowering is the most drastic change in plant development. In order to examine the involvement of ethylene in growth transition, we compared the development of ethylene-related mutants, eto1, etr1, ein2-1 and ein3-1, with the wild type (WT) in Arabidopsis thaliana. The ethylene sensitivity of two WT and the mutants is decreased in the following order: eto1 = WT < ein3-1 < ein2-1 = etr1-1. Bolting time was also delayed in nearly the same order: eto1 < WT < ein3-1 < ein2-1 < etr1. Leaf numbers increased according to the delay of bolting time, indicating that the delay of bolting time was caused by the delay of transition from vegetative to reproductive growth. Other growth parameters, including leaf area and number of flowers opening at the same time, increased in the same order, indicating that these changes were caused by a single factor, the amount of ethylene signal which was transferred though an ethylene signal transduction pathway. These results suggest that ethylene is involved in the transition from vegetative to reproductive growth in Arabidopsis thaliana.

Arabidopsis↗

PubMed2002

Thiopurine S-methyltransferase activity in Japanese subjects: metabolic activity of 6-mercaptopurine 6-methylation in different TPMT genotypes.

BACKGROUND: Thiopurine S-methyltransferase (TPMT), which exhibits autosomal codominant polymorphism, plays an important role in the metabolism of thiopurine drugs such as mercaptopurine, thioguanine and azathioprine. Decreased activity of TPMT is associated with severe hematopoietic toxicity after administration of standard doses of these drugs. METHODS: We developed a specific high-performance liquid chromatographic (HPLC) assay for measuring 6-methylmercaptopurine (6-MMP) formed from 6-mercaptopurine (6-MP) in red blood cells (RBC) lysates. The assay was used to study the distribution of TPMT activities in 44 healthy Japanese subjects with different TPMT genotypes. RESULTS: The TPMT activities in the subjects ranged from 17.9 to 37.1 pmol/h/mgHb. The TPMT activity of one subject with TPMT*1/*3C (17.9 pmol/h/mgHb) was 40% lower than the mean value of TPMT activities in 43 subjects with TPMT*1/*1 (29.6+/-4.3 pmol/h/mgHb). CONCLUSIONS: This sensitive and reproducible HPLC assay for determination of TPMT activity in RBC clinical studies has been designed to optimize dosage regimens of thiopurine drugs.

Asian People↗

PubMed2001

Bone marrow colony-forming unit assay in cats with naturally occurring myelodysplastic syndromes.

Feline myelodysplastic syndromes (MDS) has been diagnosed in many cats infected with feline leukemia virus, although the pathogenesis of this hematopoietic deficiency has been unclear. In this study, we assayed the bone marrow erythroid colony-forming units (CFU-E) and granulocyte-machrophage CFUs (CFU-GM) to investigate the pathogenesis of feline MDS. The number of CFU-E colonies was decreased in 4 of 7 cats with MDS, and the number of CFU-GM colonies was also decreased in 4 cats. Furthermore, small colonies of CFU-GM were found in all 7 cases. These findings indicated that refractory cytopenia of feline MDS could be caused by abnormal maturation and differentiation of hematopoietic stem cells in bone marrow, as it is in human MDS. The pathogenesis of feline MDS might be similar to that of human MDS.

Animals↗

PubMed2001

4-Hydroxybenzyl alcohol accumulates in suspension-cell cultures and inhibits somatic embryogenesis in carrot.

Somatic embryogenesis in carrot (Daucus carota L.) is strongly inhibited by certain factors that accumulate in culture medium of high-density cultures of embryogenic cells. We previously identified 4-hydroxybenzyl alcohol (4HBA) as one of the inhibitory factors. In this study, we analyzed the accumulation pattern of 4HBA in the cultures of carrot suspension cells. When somatic embryogenesis was induced by culturing embryogenic cells in phytohormone-free Murashige and Skoog medium at various initial cell densities, 4HBA accumulated in the culture medium. The concentration of 4HBA in high cell density cultures was higher than in low cell density cultures. The accumulation of 4HBA in high cell density cultures was rapid during the early days of culture. This rapid accumulation of 4HBA in high cell density cultures might result in the strong inhibition of somatic embryogenesis. The production of 4HBA decreased as the somatic embryos developed. In addition, embryogenic cells released larger amount of 4HBA into the culture medium compared with non-embryogenic cells. These results suggest that the production of 4HBA is both related to embryogenic competence and developmentally regulated during somatic embryogenesis.

Journal Article↗