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Articles by T Seki
Total Records ( 5 ) for T Seki
  A Abdel Nazeer , S Saito , S Sayed , L Hassan , F Askar , W Al jahdari , T Seki and O. Hideaki
  Background

Local anaesthetics exhibit direct neurotoxic effects on neurones. Numerous studies have investigated the factors that may reverse this neuropathology, but the effects of glucose conditions on neuronal regeneration after lidocaine-induced injury have not been examined by observing living neurones. The present study investigated the effects of different glucose conditions on neurite length, growth cone regeneration, and cell death in dorsal root ganglia (DRG) neurones after lidocaine-induced injury in vitro.

Methods

DRG explants were isolated from chick embryos at embryonic day 8 and cultured in media containing low, normal, or high glucose concentrations (10, 25, or 40 mM) for 24 h. Tissues were exposed to lidocaine 8 mM for 1 h, then rinsed and incubated for a further 24 h. Neurite length and growth cone collapse assays were performed to assess neuronal growth and regeneration. Lactate dehydrogenase (LDH) and caspase assays were also performed to detect neuronal cell death.

Results

Addition of lidocaine for 1 h resulted in >97% growth cone collapse and neurite destruction under all three glucose conditions. Two hours after rinsing out the lidocaine, significant reversal of growth cone collapse and neurite elongation was observed under all glucose conditions. Growth cone collapse was higher under low-glucose condition (P<0.05). High glucose negatively affected neurite length more than growth cone collapse. At 24 h, LDH release with both low- and high-glucose conditions was higher than with normal glucose (P<0.05). Low- and high-glucose conditions increased caspase 3/7 activation.

Conclusions

Normal glucose is optimal for neuronal recovery after lidocaine-induced injury in vitro.

  S Yuasa , T Onizuka , K Shimoji , Y Ohno , T Kageyama , S. H Yoon , T Egashira , T Seki , H Hashimoto , T Nishiyama , R Kaneda , M Murata , F Hattori , S Makino , M Sano , S Ogawa , O. W. J Prall , R. P Harvey and K. Fukuda
 

Rationale: The transcriptional networks guiding heart development remain poorly understood, despite the identification of several essential cardiac transcription factors.

Objective: To isolate novel cardiac transcription factors, we performed gene chip analysis and found that Zac1, a zinc finger-type transcription factor, was strongly expressed in the developing heart. This study was designed to investigate the molecular and functional role of Zac1 as a cardiac transcription factor.

Methods and Results: Zac1 was strongly expressed in the heart from cardiac crescent stages and in the looping heart showed a chamber-restricted pattern. Zac1 stimulated luciferase reporter constructs driven by ANF, BNP, or MHC promoters. Strong functional synergy was seen between Zac1 and Nkx2-5 on the ANF promoter, which carries adjacent Zac1 and Nkx2-5 DNA-binding sites. Zac1 directly associated with the ANF promoter in vitro and in vivo, and Zac1 and Nkx2-5 physically associated through zinc fingers 5 and 6 in Zac1, and the homeodomain in Nkx2-5. Zac1 is a maternally imprinted gene and is the first such gene found to be involved in heart development. Homozygous and paternally derived heterozygous mice carrying an interruption in the Zac1 locus showed decreased levels of chamber and myofilament genes, increased apoptotic cells, partially penetrant lethality and morphological defects including atrial and ventricular septal defects, and thin ventricular walls.

Conclusions: Zac1 plays an essential role in the cardiac gene regulatory network. Our data provide a potential mechanistic link between Zac1 in cardiogenesis and congenital heart disease manifestations associated with genetic or epigenetic defects in an imprinted gene network.

  H Kajiura , H Koiwa , Y Nakazawa , A Okazawa , A Kobayashi , T Seki and K. Fujiyama
 

N-Glycosylation is an important post-translational modification that occurs in many secreted and membrane proteins in eukaryotic cells. Golgi -mannosidase I hydrolases (MANI) are key enzymes that play a role in the early N-glycan modification pathway in the Golgi apparatus. In Arabidopsis thaliana, two putative MANI genes, AtMANIa (At3g21160) and AtMANIb (At1g51590), were identified. Biochemical analysis using bacterially produced recombinant AtMANI isoforms revealed that both AtMANI isoforms encode 1-deoxymannojirimycin-sensitive -mannosidase I and act on Man8GlcNAc2 and Man9GlcNAc2 structures to yield Man5GlcNAc2. Structures of hydrolytic intermediates accumulated in the AtMANI reactions indicate that AtMANIs employ hydrolytic pathways distinct from those of mammalian MANIs. In planta, AtMANI-GFP/DsRed fusion proteins were detected in the Golgi stacks. Arabidopsis mutant lines manIa-1, manIa-2, manIb-1, and manIb-2 showed N-glycan profiles similar to that of wild type. On the other hand, the manIa manIb double mutant lines produced Man8GlcNAc2 as the predominant N-glycan and lacked plant-specific complex and hybrid N-glycans. These data indicate that either AtMANIa or AtMANIb can function as the Golgi -mannosidase I that produces the Man5GlcNAc2 N-glycan structure necessary for complex N-glycan synthesis.

  H Kajiura , T Seki and K. Fujiyama
 

The core oligosaccharide Glc3Man9GlcNAc2 is assembled by a series of membrane-bound glycosyltransferases as the lipid carrier dolichylpyrophosphate-linked glycan in the endoplasmic reticulum (ER). The first step of this assembly pathway on the ER luminal side is mediated by ALG3 (asparagine-linked glycosylation 3), which is a highly conserved reaction among eukaryotic cells. Complementary genetics compared with Saccharomyces cerevisiae ALG gene families and bioinformatic approaches have enabled the identification of ALG3 from other species. In Arabidopsis thaliana, AtALG3 (At2g47760) was identified as 1,3-mannosyltransferase. Complementation analysis showed that AtALG3 rescued the temperature-sensitive phenotype, that lipid-linked oligosaccharide assemblies and that protein underglycosylation of S. cerevisiae ALG3-deficient mutant. In Arabidopsis ALG3 mutant, an immature lipid-linked oligosaccharide structure, M5ER, was synthesized, and used for protein N-glycosylation, resulting in the blockade of subsequent maturation with the concanavalin A affinoactive and Endo H-insensitive structure. N-Glycan profiling of total proteins from alg3 mutants exhibited a unique structural profile, alg3 has rare N-glycan structures including Man3GlcNAc2, M4ER, M5ER and GlcM5ER, which are not usually detected in Arabidopsis, and a much less amount of complex-type N-glycan than that in wild type. Interestingly, despite protein N-glycosylation differences compared with wild type, alg3 showed no obvious phenotype under normal and high temperature or salt/osmotic stress conditions. These results indicate that AtALG3 is a critical factor for mature N-glycosylation of proteins, but not essential for cell viability and growth in Arabidopsis.

  N Okumura , T Koh , Y Hasebe , T Seki and T. Ariga
 

Thrombin-activatable fibrinolysis inhibitor (TAFI) exhibits anti-fibrinolytic activity by removing C-terminal lysine residues from fibrin or plasminogen receptor proteins on the cellular surface, and plays an important role in the regulation of fibrinolysis. In this study, we examined the regulation of TAFI in hepatocytes during liver regeneration, and revealed its pivotal role in hepatocyte proliferation. In rat models, partial hepatectomy or carbon tetrachloride (CCl4)-induced acute liver injury suppressed the levels of plasma TAFI activity and hepatic TAFI mRNA, whereas this operation markedly increased both the hepatic plasmin activity and the level of proliferating cell nuclear antigen. In primary cultures of rat hepatocytes, the TAFI mRNA level was decreased under growth-promoting culture conditions. Treatment of the hepatocytes with TAFI siRNA increased the amount of plasmin on the hepatocytes and promoted hepatocyte proliferation. We concluded that TAFI regulates plasmin activity through its enzymatic activity whereby it reduces the plasminogen-binding capacity of the hepatocytes. The TAFI gene expression is down-regulated in hepatocyte proliferation for producing a fibrinolytic microenvironment suitable for cell growth. This is the first report on the role of TAFI in the pericellular fibrinolysis necessary for cellular proliferation.

 
 
 
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