Real-time monitoring of histamine released from rat basophilic leukemia (RBL-2H3) cells with a histamine microsensor using recombinant histamine oxidase

To detect low levels of histamine, we developed a histamine microsensor using recombinant histamine oxidase. Histamine oxidase with a histidine tag was readily purified using a histidine affinity column. The enzyme showed higher catalytic activity on histamine than diamines (e.g., putrescine and cadaverine) or N(tau)-methylhistamine. The sensor had three carbon film electrodes modified with osmium-polyvinylpyridine-based gel containing horseradish peroxidase, histamine oxidase, and Ag. When a standard solution of histamine was aspirated at a flow rate of 2 microl/min, the detected current was proportional to the histamine concentration and the lower detection limit was 11.3 nM. When rat basophilic leukemia cells (1 x 10(6)) were stimulated by various concentrations of antigen (2, 20, and 200 ng/ml), the histamine concentrations were 0.32, 2.7, and 1.3 microM, respectively, and 20 ng/ml of antigen was found to be the optimal concentration for the antigen-antibody reaction. In contrast, when thapsigargin, an inhibitor of Ca-ATPase in the endoplasmic reticulum, was added (50, 100, and 500 nM), the detected current increased with thapsigargin concentrations and the measured histamine concentrations were 28 nM, 1.3 microM, and 2.7 microM, respectively. These results indicate that the microsensor is useful for the analysis of histamine release from mast cells.

Air-cooled cold trap channel integrated in a microfluidic device for monitoring airborne BTEX with an improved detection limit

We integrated an air-cooled cold trap (CT) channel in a microfluidic device for monitoring airborne benzene, toluene, ethylbenzene, and xylene (BTEX) gases and demonstrated its effect on improving the detection limit of the microfluidic device. The device consists of concentration and detection cells formed of 3 x 1 cm Pyrex plates. We first introduced a sample gas into the concentration cell, and the gas was adsorbed onto an adsorbent in the channel. We then raised the temperature using a thin-film heater and introduced the desorbed gas into the detection cell. To prevent dilution of the gas before detection, we propose an improvement to the concentration cell structure that involves the integration of the CT channel. We examined the CT effect by comparing three types of concentration cell with different channel structures. We found that we could detect a gas concentration about 2 orders of magnitude lower than in our previous work by optimizing the channel structure and integrating a CT channel. As an example of BTEX detection,we obtained a 0.05 ppm detection limit for toluene gas with a sampling time of 30 min.

Differential measurement with a microfluidic device for the highly selective continuous measurement of histamine released from rat basophilic leukemia cells (RBL-2H3)

We fabricated a micro-fluidic device for the highly selective detection of the histamine released from rat basophilic leukemia (RBL) 2H3 cells. The device has two thin layer flow channels, each with one working electrode. One electrode was modified with Os-polyvinylpyridine based mediator containing horseradish peroxidase (Os-gel-HRP) and histamine oxidase (HAOx), the other was modified with Os-gel-HRP without any HAOx. We employed the device for differential measurement by using the HAOx modified electrode for detection and the unmodified electrode as a reference. The detection limit was greatly improved from 190 to 25 nM since the baseline noise level was suppressed. We used differential measurement to observe the histamine released from RBL-2H3 cells when stimulated with dinitrophenylated bovine serum albumin (DNP-BSA) as an antigen. We injected 5 microM of histamine solution into our device and it remained stable for more than 8 h.

A mathematical model of radiation carcinogenesis with induction of genomic instability and cell death

We developed a mathematical model of carcinogenesis that incorporates genomic instability, a feature characterized by long-term destabilization of the genome in irradiated cells that leads to an increase in cancer risk in the exposed individuals at the cancer-prone age. This model also considers the induction of cell death, another important effect of radiation on cells. It is assumed that cell killing by radiation may occur at all stages of the carcinogenic process. The resulting model can explain not only the paradoxical relationship between low mutation rates and high cancer incidence but also the low-order dose-response relationship of cancer risk.

Microfluidic device for airborne BTEX detection

We fabricated a microfluidic device for the optical detection of airborne benzene, toluene, ethylbenzene and xylenes (BTEX). The device consists of concentration and detection cells formed of 3 cm x 1 cm Pyrex plates. The concentration cell is composed of an adsorbent to concentrate the BTEX gases and a thin-film heater todesorb the concentrated gases from the adsorbent thermally. The collected gases are introduced into the detection cell, which is connected to optical fibers, to measure their absorption spectra. We optimized the device's operating conditions by studying the thermal characteristics of the concentration cell and the time profile of the gas concentration flowing in the detection cell. We used the device under optimized operating conditions to detect toluene gas as a typical example BTEX. The gas concentration amplification rate was approximately 2 orders of magnitude, and we successfully measured parts-per-million levels of toluene gas with this device.

Genetic loci controlling susceptibility to gamma-ray-induced thymic lymphoma

BALB/c is a susceptible strain for the development of gamma-ray induced mouse thymic lymphoma whereas MSM shows resistance. Association analysis of 220 backcross mice between the two strains using 67 markers was carried out to identify loci involved in the control of susceptibility. The genotype of mice with lymphoma showed excess heterozygosity relative to MSM homozygosity at D2Mit15 and D4Mit12 and was skewed toward MSM-derived alleles at D5Mit5. The P values in Mantel-Cox test were 0.0048 (D2Mit15), 0.0034 (D4Mit12) and 0.0048 (D5Mit5), suggesting association at the three loci in the susceptibility. Cooperative effect on lymphomagenesis was also observed among the three loci. To obtain independent evidence for linkage at D4Mit12, we made partially congenic mice in which a D4Mit12 region in BALB/c was replaced by MSM-derived homolog. Examination for the lymphoma susceptibility in 78 progeny of the congenic mice confirmed the effect of the locus near D4Mit12 (P=0.0037). The result, together with the linkage analysis, shows that the locus near D4Mit12 is regarded as a confirmed linkage but the other two loci as marginally suggestive.

Real-time electrochemical imaging using an individually addressable multi-channel electrode

We developed a real-time electrochemical imaging method that uses a multiple enzyme-modified microelectrode. The method will enable the investigation of the functions of biological materials and cells. To test its effectiveness, we imaged the two-dimensional concentration distribution for hydrogen peroxide and L-glutamate in a standard solution. The multiple electrode consists of an 8 x 8 array of 30 x 30 microm2 carbon micro electrode. Each electrode was connected to a 64-channel potentiostat that could apply a potential to all electrodes at the same time. The multiple electrode was coated with an Os-polyvinylpyridine based polymer (Os-gel) containing horse radish peroxidase (HRP) to detect hydrogen peroxide, which is a very common product of oxidase enzyme. When measuring glutamate, which is a well-known neurotransmitter in the mammalian central nerve system, we modified the electrode with a bilayer of Os-gel-HRP and GluOx. The detection limit of our method was 1 microM and images of the glutamate concentration-distribution changes induced by local injection of glutamate through microcapillary were obtained in real time.

Cytoplasmic microtubular system implicated in de novo formation of a Rabl-like orientation of chromosomes in fission yeast

Chromosomes are not packed randomly in the nucleus. The Rabl orientation is an example of the non-random arrangement of chromosomes, centromeres are grouped in a limited area near the nuclear periphery and telomeres are located apart from centromeres. This orientation is established during mitosis and maintained through subsequent interphase in a range of species. We report that a Rabl-like configuration can be formed de novo without a preceding mitosis during the transition from the sexual phase to the vegetative phase of the life cycle in fission yeast. In this process, each of the dispersed centromeres is often associated with a novel Sad1-containing body that is contacting a cytoplasmic microtubule laterally (Sad1 is a component of the spindle pole body (SPB)). The Sad1-containing body was colocalized with other known SPB components, Kms1 and Spo15 but not with Cut12, indicating that it represents a novel SPB-related complex. The existence of the triplex structure (centromere-microtubule-Sad1 body) suggests that the clustering of centromeres is controlled by a cytoplasmic microtubular system. Accordingly, when microtubules are destabilized, clustering is markedly reduced.

Real-time multisite observation of glutamate release in rat hippocampal slices

A multichannel glutamate sensor was fabricated that consists of enzyme modified electrodes and has a high sensitivity and selectivity to glutamate. We placed a rat hippocampal slice on the sensor and monitored the current at four electrodes resulting from the stimulation with muscimol, a gamma-aminobutyric acid(A) (GABA(A)) receptor agonist. We obtained different glutamate concentration increases at the different positions, suppressed by bicuculline, a GABA(A) receptor antagonist. This demonstrated that the sensor can monitor the glutamate released via GABA(A) receptors pathways, and the difference in the concentrations may indicate differences in the distribution of GABA(A) receptor as well as diverse receptor functions. This multichannel sensor may be useful for non-invasive, real-time monitoring of glutamate distribution, which would make it a valuable tool for pharmacological analysis.

Detection of electrochemical enzymatic reactions by surface plasmon resonance measurement

We describe the surface plasmon resonance (SPR) detection of an enzymatic turnover reaction and the measurement of glucose concentration using a multienzyme layer modified gold electrode. We constructed an osmium redox polymer mediated enzyme sensor on a gold thin-film electrode and monitored electrochemical reaction by SPR measurement. Unlike the usual binding assay with SPR, here we used SPR to detect the redox state of an electron mediator that was the result of the electron-transfer reaction of sequential enzymatic reactions. Therefore, the degree of refractive index change was independent of the dielectric property of the substrate and enzymatic molecular recognition was converted to refractive index change with amplification. For the quantitative evaluation of glucose with this method, we used chronopotentiometry and a linear relation was obtained between the glucose concentration and the rate of refractive index change.

Allelic loss mapping and physical delineation of a region harboring a thymic lymphoma suppressor gene on mouse chromosome 16

Our previous mapping of allelic loss in gamma-ray induced thymic lymphomas in F(1) hybrid and backcross mice between BALB/c and MSM strains identified three regions with high frequencies of allelic loss which probably harbor a tumor suppressor gene. One region, Tlsr7, exists near the D16 Mit122 locus on chromosome 16. This study has further localized Tlsr7 by constructing a physical map and scanning a total of 587 thymic lymphomas. The map consists of 13 overlapping BAC clones and isolation of BAC-derived polymorphic probes leads to fine mapping of allelic losses. Eleven lymphomas show informative breakpoints of allelic loss regions relative to the flanking markers on the map. Pulsed-field gel electrophoresis of NotI digests of the clones shows that the commonly lost region is localized within an approximately 300 kb interval near D16Mit192. This map is invaluable to facilitate the identification of genes in the Tlsr7 region.

Untargeted mutation of the maternally derived mouse hypervariable minisatellite allele in F1 mice born to irradiated spermatozoa

Length change mutation at the Ms6hm hypervariable mouse minisatellite locus was analyzed in C57BL/6N x C3H/HeN F(1) mice and the F(1) of the reciprocal cross born to irradiated male parents. Spontaneous mutant frequencies were 8.4% and 9.8% for the paternally derived and maternally derived C3H/HeN alleles, respectively. The mutant frequencies for the paternally derived allele increased to 22% and 19% when the male parents were irradiated with 6 Gy at the postmeiotic spermatozoa stage and the spermatogonia stage, respectively. These increases in the mutant frequency were at least 10 to 100 times higher than those expected from the frequency of hits to the 3- to 4-kb allele, suggesting that the length change mutation at this minisatellite locus was not a targeted event due directly to DNA damage in the region. Further analysis demonstrated that the mutant frequency increased also at the maternally derived C3H/HeN allele to 20% when the male parents were irradiated at the spermatozoa stage. This increase in the maternal allele mutation was not observed in F(1) born to irradiated spermatogonia. The present study suggests that introduction of DNA damage by irradiated sperm triggers genomic instability in zygotes and in embryos of subsequent developmental stages, and this genomic instability induces untargeted mutation in cis at the paternally derived minisatellite allele and in trans at the maternally derived unirradiated allele. Untargeted mutation revealed in the present study defines a previously unnoticed genetic hazard to the maternally derived genome by the paternally introduced DNA damage.

Increased frequencies of gene and chromosome mutations after X-irradiation in mouse embryonal carcinoma cells transfected with the bcl-2 gene

Preimplantation stage mouse embryos are known to be highly sensitive to the killing effect of DNA-damaging agents such as radiation. Interestingly, however, this stage of development is well protected from radiation induction of malformation and carcinogenesis in postnatal life. In recent years, it has become clear that the stem cells of preimplantation stage embryos undergo extensive apoptosis after DNA damage. It has been postulated that this apoptosis is likely to be responsible for the resistance to malformation, by excluding cells carrying deleterious DNA damage. We have tested the possible role of apoptosis in elimination of gene and chromosome mutations in undifferentiated mouse embryonal carcinoma cell line, F9, transfected with human bcl-2 cDNA. The colony radiosensitivity of F9 cells was not affected by overexpression of the bcl-2 gene, but the apoptotic cell death was suppressed, as examined by DNA ladder assay and Hoechst staining. This suppression was accompanied by an increase in the frequencies of hprt mutation and micronucleus formation after X-irradiation. These results support the idea that maintenance of genomic integrity during early development is likely to be executed by apoptotic elimination of cells at risk.

Miniaturized thin-layer radial flow cell with interdigitated ring-shaped microarray electrode used as amperometric detector for capillary electrophoresis

A chip-type thin-layer radial flow cell was developed as an amperometric detector for capillary electrophoresis. We fabricated a carbon film-based interdigitated ring-shaped array (IDRA) microelectrode with a 2 microm bandwidth and an almost 1 microm gap on a glass plate and used it as a working electrode. A fused-silica capillary was arranged above the IDRA electrode using a guide hole drilled through the acryl plate that formed the flow cell lid. A flow channel for use in connecting the outlet capillary was also fabricated in the acryl plate. We characterized the analytical performance of the IDRA electrode in the microchip flow cell in terms of linear concentration range, sensitivity and concentration detection limit. We achieved a collection efficiency and catechol redox cycle at the IDRA microelectrode of 65% and 1.71, respectively, and thus a high sensitivity and low detection limit of 392.9 pA/microM and 15 nM for dopamine hydrochloride. We examined the reproducibility of the detector and found that the run-to-run and detector-to-detector relative standard deviations were both less than 10%.

The effect of caffeine on p53-dependent radioresponses in undifferentiated mouse embryonal carcinoma cells after X-ray and UV-irradiations

The effect of caffeine was studied on the radioresponses of undifferentiated mouse embryonal carcinoma cells (EC cells) with or without the functional p53. The radioresponses studied included radiosensitivity, the activation of p53, apoptosis with characteristic DNA ladder formation and cell cycle progression. An undifferentiated mouse EC cell line, ECA2, and a newly established p53-deficient EC cell line, p53 delta, were used in the present study. The status of the p53 gene did not significantly affect the colony survivals of undifferentiated EC cells to X-rays and UV. Although a post-irradiation treatment with caffeine sensitized both lines to X-rays marginally, the sensitization was prominent for UV regardless of the p53 status of the cells. The activation of a p53 responsible lacZ reporter construct was observed in stably transfected ECA2 cells after X-ray and UV irradiations. Caffeine suppressed the X-ray induced activation of the lacZ reporter, while it drastically enhanced the activation after UV irradiation. X-rays and UV readily triggered the apoptosis of ECA2 cells with the characteristic DNA ladder. Although UV-induced DNA ladder formation was enhanced by caffeine, that induced by X-rays was unaffected. Therefore, the effects of caffeine on the p53-dependent radioresponses were found to be agent specific: suppression for the X-ray induced and augmentation for the UV induced. In contrast to p53-proficient ECA2 cells, smear-like DNA degradation was observed for irradiated p53 delta cells, suggesting the presence of a mode of cell death without DNA ladder formation. UV induction of the smear-like DNA degradation was enhanced in the presence of caffeine. Regardless of the state of the p53 gene, G1/S arrest was not observed in X-ray and UV irradiated EC cells. X-ray induced G2/M arrest in both lines, which was abrogated by caffeine, while G2/M arrest after UV was unaffected by a caffeine treatment. These results indicate that the radioresponses of undifferentiated EC cells differ considerably from those of somatic cells, and that these radioresponses were modulated by a post-irradiation treatment with caffeine.

Telomere-led bouquet formation facilitates homologous chromosome pairing and restricts ectopic interaction in fission yeast meiosis

A polarized chromosomal arrangement with clustered telomeres in a meiotic prophase nucleus is often called bouquet and is thought to be important for the pairing of homologous chromosomes. Fluorescence in situ hybridization in fission yeast indicated that chromosomal loci are positioned in an ordered manner as anticipated from the bouquet arrangement. Blocking the formation of the telomere cluster with the kms1 mutation created a disorganized chromosomal arrangement, not only for the regions proximal to the telomere but also for interstitial regions. The kms1 mutation also affected the positioning of a linear minichromosome. Consistent with this cytological observation, the frequency of ectopic homologous recombination between a linear minichromosome and a normal chromosome increased in the kms1 background. Intragenic recombination between allelic loci is reduced in the kms1 mutant, but those between non-allelic loci are unaffected or slightly increased. Thus, telomere-led chromosome organization facilitates homologous pairing and also restricts irregular chromosome pairing during meiosis.

Transient infiltration of neutrophils into the thymus in association with apoptosis induced by whole-body X-irradiation

Generally, the process of apoptosis does not cause leakage of noxious cytosolic contents and is therefore non-inflammatory. However, as previously shown, macrophages ingesting apoptotic CTLL-2 cells produced pro-inflammatory cytokines, particularly interleukin-8 (IL-8) and macrophage inflammatory protein-2 (MIP-2), a murine IL-8 homolog. This predicted that rapid and massive apoptosis may induce neutrophil accumulation in vivo. In this study, we tested this prediction by inducing apoptosis by whole-body X-irradiation in mice. After exposure to 4 Gy X-ray irradiation, mice exhibited considerable apoptosis of thymic cells, which was associated with transient infiltration of neutrophils as well as MIP-2 mRNA expression. In contrast, in p53-deficient mice in which irradiation-induced apoptosis was suppressed, as has been reported, infiltration of neutrophils into the thymus was less than that found in p53+/+ mice. Taken together, these results suggest that massive and rapid apoptosis can result in infiltration of neutrophils.

mRNAs encoding zinc finger protein isoforms are expressed by alternative splicing of an in-frame intron in fission yeast

We report here that a gene encoding a protein with three zinc fingers is expressed predominantly to produce a protein containing only two zinc fingers in the fission yeast Schizosaccharomyces pombe. A third zinc finger resides within the in-frame intron that is normally spliced out. By RT-PCR analysis, we detected a minor transcript encoding a protein with three zinc fingers. Such alternative splicing for assortment of zinc finger domains have been reported in animals and implicated in switching of the target genes expressed specifically during development. This is the first report of the occurrence of such zinc finger assortment in lower eucaryotes.

The polyubiquitin gene is essential for meiosis in fission yeast

We isolated a novel sporulation-deficient mutant of Schizosaccharomyces pombe. The mutant did not have a mitotic growth defect but aborted meiosis at the first or the second division with condensed chromosomes that failed to separate, abnormal spindle(s), and disintegrated spindle pole bodies (SPBs). During the first division, the centromeres were pulled to near the spindle poles but condensed divalent chromosomes remained at the center. The failure to proceed to anaphase was also observed during a time-lapse recording of a SPB protein tagged with green fluorescent protein. The polyubiquitin gene ubi4(+), which encoded eight ubiquitins fused in tandem, complemented this mutant. The mutation, an A to G substitution, was identified within the ubi4(+) gene at the ATG initiation codon. Disruption of the ubi4(+) gene produced the same phenotypes. The ubi4(+) mRNA was strongly induced for meiosis. However, ubiquitin increases only slightly, suggesting that the role of the polyubiquitin gene is to supply ubiquitin that is consumed by unidentified mechanisms. Before the ubi4 mutant cells entered meiosis, ubiquitin was greatly decreased indicating that shortage of ubiquitin caused abortion of meiosis. This work provides insights for the role of polyubiquitin gene and importance of ubiquitination in SPB integrity at the meiotic divisions.

Down-regulation of nuclear factor kappaB is required for p53-dependent apoptosis in X-ray-irradiated mouse lymphoma cells and thymocytes

Transcription factors p53 and nuclear factor kappaB (NF-kappaB) have been implicated in apoptosis induced by DNA-damaging agents, but the relationship between these two factors at the molecular level is largely unknown. We have isolated apoptosis-resistant mutant sublines from a radiosensitive mouse lymphoma 3SB cell line that undergoes p53-depen-dent apoptosis after X-ray irradiation, and we have analyzed the NF-kappaB activity. Two of these apoptosis-resistant sublines expressed mutant p53 protein and exhibited a defect in the induction of cyclin-dependent kinase inhibitor p21 after X-ray irradiation. A decrease in the DNA binding activity of NF-kappaB was observed in the parental 3SB cells after exposure to X-rays, whereas the same activity was unaffected by radiation in the two mutant sublines. A similar down-regulation of NF-kappaB activity by X-rays was observed in thymocytes derived from p53 wild-type and heterozygous mice, but not in thymocytes from p53 homozygous knock-out mice. These results suggest that NF-kappaB inactivation is p53 dependent and is required for X-ray-induced apoptosis in thymic lymphoma cells and normal thymocytes.