Transition of the blastomere cell cycle from cell size-independent to size-dependent control at the midblastula stage in Xenopus laevis.

Dissociated animal cap blastomeres of Xenopus laevis blastulae were cultured at a low Ca level (1 microM) from 9th to 18th cell cycle at 22 +/- 1 degrees C and observed by a time-lapse video recorder. Blastomeres cleaved unequally to increase variability in cell size as cell cycles progressed, but synchronously at a constant cell cycle time of about 30 min up to the 12th cleavage in diploid cells, and up to the 13th cleavage in haploid cells, regardless of their cell sizes. Thereafter, blastomeres cleaved asynchronously at varying cell cycle times in proportion to the inverse square of their radii.

Protective role of intracellular glutathione against nitric oxide-induced necrosis in rat gastric mucosal cells.

Background: Nitric oxide synthase activity is increased in the stomach in association with Helicobacter pylori infection and portal hypertension, but the mechanism by which nitric oxide contributes to mucosal damage remains unclear.

Aim: To examine whether nitric oxide injures gastric mucosal cells and whether cellular glutathione affects nitric oxide-induced cytotoxicity.

Methods: A confluent monolayer of RGM-1 gastric mucosal cells was exposed to nitric oxide donors (NOC5 or NOC12).

Synthesis and antibacterial activity of novel 7-substituted-6-fluoro-1- fluoromethyl-4-oxo-4H-[1,3thiazeto[3,2-a]quinoline-3-carboxylic acid derivatives.

A series of 7-substituted-6-fluoro-1-fluoromethyl-4-oxo-4H- [1,3]thiazeto[3,2-a]quinoline-3-carboxylic acid derivatives (2a-1) was prepared and evaluated for antibacterial activity. These compounds were obtained by deacylation of 4-benzoyloxy-2-(1-chloro-2-fluoroethyl)thio-6,7- difluoroquinoline-3-carboxylate (10) and subsequent intramolecular cyclization followed by substitution with cyclic amines and then hydrolysis. The intramolecular cyclization reaction of 18, one of the diastereomers (17, 18) revealed that the cyclization reaction proceeded through an inversion to afford (-)-11a in good chemical and optical yield.

P-selectin inhibition prevents early neutrophil activation but provides only modest protection against myocardial injury in dogs with ischemia and forty-eight hours reperfusion.

Objectives: This study was designed to determine whether antibody neutralization of the adhesion protein P-selectin would prevent neutrophil activation and reduce myocardial reperfusion injury.

Background: Although inhibition of P-selectin markedly reduces short-term myocardial injury after ischemia and reperfusion, it is unknown whether it can provide meaningful long-term protection and preserve left ventricular function.

Methods: Closed-chest dogs underwent 90 min left anterior descending coronary artery occlusion and 48 h reperfusion, and were randomized to 1) a treatment group (n = 11) receiving 1 mg/kg of the blocking anti-P-selectin antibody PB1.

Effect of vitamin E in gastric mucosal injury induced by ischaemia-reperfusion in nitric oxide-depleted rats.

Background: Neutrophil infiltration and lipid peroxide accumulation are involved in reperfusion-induced gastric mucosal injury in nitric oxide-depleted rats.

Aim: To assess the effect of vitamin E on this injury.

Methods: After ischaemia-reperfusion, the total area of erosions, lipid peroxide contents in gastric mucosa, and gastric neutrophil accumulation were compared between nitric oxide-depleted rats with deficient, normal, and increased vitamin E intake over 8 weeks.

Cell cycle transition in early embryonic development of Xenopus laevis.

This article reviews cell cycle changes that occur during midblastula transition (MBT) in Xenopus laevis based on research carried out in the authors' laboratory. Blastomeres dissociated from the animal cap of blastulae, as well as those in an intact embryo, divide synchronously with a constant cell cycle duration in vitro, up to the 12th cell cycle regardless of their cell sizes. During this synchronous cleavage, cell sizes of blastomeres become variable because of repeated unequal cleavage.

Inhibition of stress-stimulated colonic propulsion by alpha 2-adrenoceptor antagonists in rats.

Alpha2-adrenoceptor antagonists have been reported to stimulate colonic motor activity, but the effect on colonic motor dysfunction is unclear. We have investigated the effect of alpha 2-adrenoceptor antagonists on wrap-restraint stress-stimulated and normal colonic propulsion in rats. Colonic propulsion was evaluated by the transit of a charcoal marker along the colon.

Detection of cytotoxic effects of Clostridium novyi type A on bovine kidney cells.

The cytotoxic effects of a toxic preparation from Clostridium novyi type A were demonstrated on tissue-cultured bovine kidney cells. The cytotoxic response was dose-dependent and could be neutralized by homologous antiserum. Scanning electron microscopy revealed damaged kidney cell surfaces.

A randomized trial of aspirin versus cilostazol therapy after successful coronary stent implantation.

Percutaneous transluminal coronary angioplasty (PTCA) is widely used to treat patients with ischemic heart disease, but the procedure involves a number of problems, including acute coronary occlusion and restenosis. Although stents have proved useful for preventing post-PTCA restenosis, especially elastic recoil during the acute phase, no method has yet been established to prevent restenosis caused by vascular smooth muscle cell proliferation in the late phase. Cilostazol selectively inhibits the 3'5'-cyclic-nucleotide phosphodiesterase (PDE) III (cyclic guanosine monophosphate-inhibited PDE) of the cyclic adenosine monophosphate PDE family; it also has antithrombotic and vasodilating effects, as well as an inhibitory effect on vascular smooth muscle cell proliferation through PDE III inhibition.

Role of amphibian egg transglutaminase in the development of secondary cytostatic factor in vitro.

Fresh cytosols extracted from unfertilized amphibian eggs contain a cytostatic factor (CSF) which arrests the cell cycle at metaphase when microinjected into cleaving blastomeres. This CSF is sensitive to Ca2+, and is designated primary CSF (1 degree CSF). During storage of Ca(2+)-containing cytosols at 2 degrees C, stable CSF activity appears, designated secondary CSF (2 degrees CSF).

Microtubule dependence of chromosome cycles in Xenopus laevis blastomeres under the influence of a DNA synthesis inhibitor, aphidicolin.

The spindle-assembly checkpoint of the cell cycle develops in Xenopus laevis embryos at the midblastula transition (MBT). Our previous experiments using animal-cap blastomeres indicate that the checkpoint is regulated by a mechanism that depends on age, but not on the nucleocytoplasmic (N/C) ratio (Clute and Masui, 1995). In the present study, the time of appearance of the spindle-assembly checkpoint is examined in animal-cap blastomeres whose N/C ratio is reduced by treatment with aphidicolin.

The role of Ca(2+) in progesterone-induced germinal vesicle breakdown of Xenopus laevis oocytes: the synergic effects of microtubule depolymerization and Ca(2+).

By monitoring (45)Ca(2+) influx and efflux from oocytes a transient increase followed by a transient decrease in the Ca(2+)-content of progesterone-treated oocytes was observed. Chelation of intracellular Ca(2+) with EGTA or BAPTA-type buffers inhibited progesterone-induced GVBD. Buffers with a mid-range Kd (∼1.

The role of microtubules and inositol triphosphate induced Ca2+ release in the tyrosine phosphorylation of mitogen-activated protein kinase in extracts of Xenopus laevis oocytes.

Microsomal fractions of Xenopus oocytes release preloaded 45 Ca2+ when treated with inositol triphosphate (InsP3). The effective concentration of InsP3 required for half-maximal release (EC50) is 59 nM and maximal release occurs at approximately 2 microM InsP3. Uptake and release of 45 Ca2+ are not altered by the catalytic subunit of protein kinase A, dibutyrl cyclic adenosine monophosphate, protein kinase A peptide inhibitor or nocodazole.

Calcium-dependent development of secondary cytostatic factor (2 degrees CSF) from Xenopus laevis oocytes and zygotes.

Fresh cytosols extracted from unfertilised eggs of Xenopus laevis contain a cytostatic factor (CSF) which arrests the cell cycle at metaphase when microinjected into cleaving blastomeres. This CSF is sensitive to Ca2+ and is designated primary CSF (1 degrees CSF). During storage of Ca2(+)-containing cytosols at 2 degrees C, a stable CSF activity appears which is designated secondary CSF (2 degrees CSF).

A quest for cytoplasmic factors that control the cell cycle.

Between 1966 and 1986 the author and his former students carried out an investigation into the cytoplasmic factors that regulate nuclear behaviour during meiotic maturation of oocytes. This anecdotal chronicle traces the development of the problems and the direction in which their solutions were attempted in the course of this investigation. The author examines why he decided to study oocyte maturation, how he discovered progesterone as a maturation-inducing hormone and maturation promoting factor (MPF) and cytostatic factor (CSF) as meiosis-controlling factors, how the idea of the cell cycle without the cell occurred to him, and how it was materialised by invention of a cell-free system.

Activation of newt eggs in the absence of Ca activity by treatment with cycloheximide or D O.

Unfertilized eggs of urodeles that exhibit physiological polyspermy are difficult to activate by ordinary egg-activating agents, such as pricking and Ca ionophores, that easily activate monospermic anuran eggs. Therefore, we have tested the effects of other agents that cause egg activation in non-amphibian species in order to investigate the mechanism of egg activation in urodeles. We have found that cycloheximide (a protein synthesis inhibitor), D O (that induces microtubule polymerization) and 6-DMAP (a protein kinase inhibitor) caused activation of unfertilized eggs of the newt, Cynops pyrrhogaster.

Regulation of the appearance of division asynchrony and microtubule-dependent chromosome cycles in Xenopus laevis embryos.

Divisions of animal-cap blastomeres dissociated from Xenopus laevis embryos are synchronous mostly up to 12th cleavage or the 13th cell cycle, but become asynchronous afterward, during the midblastula transition (MBT), and at the same time, chromosome cycles become microtubule-dependent and are arrested in mitosis if treated with nocodazole. To investigate causes for these changes in cell-cycle control, we observed division synchrony in animal-cap blastomeres dissociated from embryos whose nucleocytoplasmic ratio (N/C) had been altered by constriction of zygotes or by delaying nucleation into zygote halves and compared their mitotic indices in the presence and absence of nocodazole. Thus, we found that asynchronous divisions always commenced when N/C reached the value of 128 to 256 times that of an animal blastomere of the 32-cell embryo, corresponding to the 12th and 13th cycles of a normal embryo, while the number of synchronous cycles became variable, ranging from 9 to 14, depending on the initial N/C.

Purification and properties of two chitinases from Streptomyces sp. J-13-3.

Two chitinases (Chi-A and Chi-B) purified from Streptomyces sp. J-13-3 had the same molecular weights (31,000) and enzymatic properties (optimum pH and temperature of pH 6.0 and 45 degrees C) but had significantly different isoelectric points (3.

Metaphase arrest in newly matured or microtubule-depleted mouse eggs after calcium stimulation.

In mouse eggs arrested at meiotic metaphase II, the increase in intracellular calcium that results from fertilisation induces nuclear formation in both newly ovulated and older eggs. In contrast, the calcium increase that results from exposure to the calcium ionophore A23187 induces nuclear formation in older, but not young, newly ovulated eggs. When treated with the microtubule inhibitor colcemid, and fertilised, young eggs remained at metaphase, but many older eggs formed nuclei, although older eggs treated with colcemid and A23187 remained at metaphase.

Structure and action of MIP (Mytilus inhibitory peptide)-related tetrapeptides synthesized with a multipeptide synthesizer.

Using a multipeptide synthesizer we synthesized 19 peptide libraries, each of which consisted of 19 MIP-related tetrapeptides, and isolated a number of peptides, which have an inhibitory effect on phasic contraction of the ABRM of Mytilus, from the libraries. To the present, the structures of about 30 species of the peptides were determined, and the peptides with the determined structures were synthesized. The structure and action of each synthetic peptide was compared with those of others to explain structure-activity relationship of MIPs.

Maintenance of metaphase in colcemid-treated mouse eggs by distinct calcium- and 6-dimethylaminopurine (6-DMAP)-sensitive mechanisms.

In mouse eggs, the arrest at meiotic metaphase II is released by the fertilization-induced increase in intracellular calcium. When eggs treated with the microtubule inhibitor colcemid are fertilized or exposed to the calcium ionophore A23187, normal calcium increases occur, but the eggs remain at metaphase. However, when colcemid-treated eggs are fertilized or A23187-treated and then exposed to the protein kinase inhibitor 6-dimethylaminopurine (6-DMAP), they enter interphase.

[Detection of neural crest tumors by 123I-MIBG scintigraphy].

From January 1993 to January 1994, scintigraphy with 123I-MIBG and/or 131I-MIBG were performed in 22 patients and their scintigraphic usefulness was evaluated. Iodine-123 MIBG and 131I-MIBG scintigrams were obtained 24 hours after injection of 222 MBq of 123I-MIBG and 48 hours after injection of 20 MBq of 131I-MIBG, respectively. In two patients with pheochromocytoma, the 123I-MIBG and 131I-MIBG scans were performed and both images were compared.

Enhancement of mouse egg activation by the kinase inhibitor, 6-dimethylaminopurine (6-DMAP).

Metaphase arrest in vertebrate eggs is maintained by the action of cytostatic factor (CSF) on maturation promoting factor (MPF). In amphibian eggs, the kinase inhibitor, 6-dimethylaminopurine (6-DMAP) inactivates both CSF and MPF, resulting in the release from metaphase and entry into interphase. In the mouse, 6-DMAP induces nuclear formation in maturing oocytes, but not in eggs at metaphase II.