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Biomedical subjects

M Kai

Publications and source records attributed to M Kai.

At least 91 records · Page 5Linked to original sources
PubMed1998

Overexpression of S-adenosylmethionine decarboxylase (SAMDC) in early Xenopus embryos induces cell dissociation and inhibits transition from the blastula to gastrula stage.

Xenopus early embryos contain relatively low levels of S-adenosyl-methionine decarboxylase (SAMDC) and its mRNA. When SAMDC mRNA was injected into Xenopus embryos, it was preserved until the blastula stage and induced a large increase in SAMDC activity. The SAMDC-overexpressed embryos developed normally until the blastula stage but at the early gastrula stage cells which received the mRNA, dissociated autonomously and stopped synthesizing protein. In a hypotonic medium, the dissociated cells, and hence whole embryos, autolyzed. However, in isotonic media dissociated cells did not autolyze, although they did not divide and their DNA and RNA synthesis activity was greatly inhibited. The effects of SAMDC overexpression were abolished by coinjection of ethylglyoxal-bis(guanylhydrazone) (EGBG), a specific inhibitor of SAMDC. In SAMDC-overexpressed embryos the level of putrescine decreased and that of spermidine increased, though to limited extents, resulting in a considerable decrease in the putrescine/spermidine ratio. However, direct injection of spermidine did not mimic the effect of SAMDC overexpression, and putrescine coinjected with SAMDC mRNA to maintain the normal putrescine/spermidine ratio did not rescue the embryos. Conversely, the level of S-adenosylmethionine (SAM) greatly decreased and coinjection of SAM, which restored the level of SAM, rescued the embryos. We concluded that in SAMDC-overexpressed embryos a SAM-deficient state was induced and this caused cell dissociation and inhibition of transition from the blastula to gastrula stage. We suggest that the SAM-deficient embryos obtained in the present study provide a unique system for studying the cellular control mechanism underlying the blastula-gastrula transition.

Adenosylmethionine Decarboxylase↗
PubMed1997

A structure-specific endonuclease from cauliflower (Brassica oleracea var. botrytis) inflorescence.

A protein with structure-specific endonuclease activity has been purified to near homogeneity from cauliflower ( Brassica oleracea var. botrytis) inflorescence through five successive column chromatographies. The protein is a single polypeptide with a molecular mass of 40 kDa. Using three different branched DNA structures (flap, pseudo-Y and stem-loop) we found that the enzyme, a cauliflower structure-specific endonuclease, cleaved the single-stranded tail in the 5'-flap and 5'-pseudo-Y structures, whereas it could not incise the 3'-flap and 3'-pseudo-Y structures. The incision points occur around the single strand-duplex junction in these DNA substrates and the enzyme leaves 5'-PO4 and 3'-OH termini on DNA. The protein also endonucleolytically cleaves on the 3'-side of the single-stranded region at the junction of unpaired and duplex DNA in the stem-loop structure. The structure-specific endonuclease activity is stimulated by Mg2+ and by Mn2+, but not by Ca2+. Like mammalian FEN-1, the protein has weak 5'-->3' double-stranded DNA-specific exonuclease activity. These results indicate that the cauliflower protein is a plant structure-specific endonuclease like mammalian FEN-1 or may be the plant alternative.

Brassica↗
PubMed1997

Cloning and characterization of two human isozymes of Mg2+-independent phosphatidic acid phosphatase.

We obtained two human cDNA clones encoding phosphatidic acid phosphatase (PAP) isozymes named PAP-2a (Mr = 32,158) and -2b (Mr = 35, 119), both of which contained six putative transmembrane domains. Both enzymes were glycosylated and cleaved by N-glycanase and endo-beta-galactosidase, thus suggesting their post-Golgi localization. PAP-2a and -2b shared 47% identical sequence and were judged to be the human counterparts of the previously sequenced mouse 35-kDa PAP(83% identity) and rat Dri42 protein (94% identity), respectively. Furthermore, the sequences of both PAPs were 34-39% identical to that of Drosophila Wunen protein. In view of the functions ascribed to Wunen and Dri42 in germ cell migration and epithelial differentiation, respectively, these findings unexpectedly suggest critical roles of PAP isoforms in cell growth and differentiation. Although the two PAPs hydrolyzed lysophosphatidate and ceramide-1-phosphate in addition to phosphatidate, the hydrolysis of sphingosine-1-phosphate was detected only for PAP-2b. PAP-2b was expressed almost ubiquitously in all human tissues examined, whereas the expression of PAP-2a was relatively variable, being extremely low in the placenta and thymus. In HeLa cells, the transcription of PAP-2a was not affected by different stimuli, whereas PAP-2b was induced (up to 3-fold) by epidermal growth factor. These findings indicate that despite structural similarities, the two PAP isozymes may play distinct functions through their different patterns of substrate utilization and transcriptional regulation.

Amino Acid Sequence↗
PubMed1997

Phosphatidic acid phosphatase from mammalian tissues: discovery of channel-like proteins with unexpected functions.

Phosphatidic acid phosphatase (PAP) has long been known as a key enzyme involved in both glycerolipid biosynthesis and cellular signal transduction. The cDNA cloning of a plasma membrane-bound type 2 PAP has revealed the existence of a novel glycoprotein with six transmembrane domains. The type 2 PAP now represents an enzyme family consisting of Drosophila Wunen and rat Dri 42, which participate in germ cell migration and epithelial differentiation, respectively. Such novel functions of the type 2 PAP suggest the unexpected importance of lipids and/or their metabolic enzymes.

Amino Acid Sequence↗
PubMed1997

Promotion of transferrin folding by cyclic interactions with calnexin and calreticulin.

Calnexin, an abundant membrane protein, and its lumenal homolog calreticulin interact with nascent proteins in the endoplasmic reticulum. Because they have an affinity for monoglucosylated N-linked oligosaccharides which can be regenerated from the aglucosylated sugar, it has been speculated that this repeated oligosaccharide binding may play a role in nascent chain folding. To investigate the process, we have developed a novel assay system using microsomes freshly prepared from pulse labeled HepG2 cells. Unlike the previously described oxidative folding systems which required rabbit reticulocyte lysates, the oxidative folding of transferrin in isolated microsomes could be carried out in a defined solution. In this system, addition of a glucose donor, UDP-glucose, to the microsomes triggered glucosylation of transferrin and resulted in its cyclic interaction with calnexin and calreticulin. When the folding of transferrin in microsomes was analyzed, UDP-glucose enhanced the amount of folded transferrin and reduced the disulfide-linked aggregates. Analysis of transferrin folding in briefly heat-treated microsomes revealed that UDP-glucose was also effective in elimination of heat-induced misfolding. Incubation of the microsomes with an alpha-glucosidase inhibitor, castanospermine, prolonged the association of transferrin with the chaperones and prevented completion of folding and, importantly, aggregate formation, particularly in the calnexin complex. Accordingly, we demonstrate that repeated binding of the chaperones to the glucose of the transferrin sugar moiety prevents and corrects misfolding of the protein.

Calcium-Binding Proteins↗
PubMed1997

Sequence analysis of a 685-kb genomic region on chromosome 3p22-p21.3 that is homozygously deleted in a lung carcinoma cell line.

Frequent chromosomal aberrations and/or losses of heterozygosity involving the short arm of chromosome 3 in carcinomas of the lung, kidney and other tissues imply that multiple putative tumor suppressor genes may be present on this chromosomal arm. To search for one of these genes, we determined DNA sequences in the genomic region at 3p22-21.3 where we had previously detected a homozygous deletion in a lung cancer cell line. The DNA sequence results of an about 685-kb region indicated that the size of the homozygously deleted segment was 638,489 bp, in which we identified only four genes including the integrin alpha RLC and the trans-Golgi p230 genes, both reported previously. The predicted amino acid sequences of one of the two novel genes showed high homology to villin, a human cytoskeleton protein; those of the other gene, termed HYA22, revealed significant homology to YA22, a hypothetical protein predicted from DNA sequences of Schizosaccharomyces pombe. The computer programs HEXON or GRAIL were able to predict three-fourths of the exons; the smallest exon predicted by either program was 46 base pairs. Repetitive sequences contained in the genomic region included 151 copies of the Alu sequence (1 copy/every 4.5 kb), 19 copies of the L1 sequence (1 copy/every 36 kb), and 10 copies of the THE sequence.

Amino Acid Sequence↗
PubMed1997

High-performance liquid chromatographic separation of kyotorphin, a basic Tyr-Arg dipeptide, in rat brain tissue and quantification using fluorimetric detection.

Two HPLC procedures based on sample derivatization at the N-terminal Tyr moiety with agents yielding fluorescent derivatives were applied to the selective and sensitive detection as well as quantification of the basic kyotorphin, Tyr-Arg dipeptide, in rat brain tissue. The first one is a post-column fluorescence derivatization method, whereby the peptides extracted from the brain tissue are separated on an octadecylsilyl-silica gel column, followed by on-line fluorescence derivatization for detection. The other one is a pre-column derivatization method, where the extracted peptides are first reacted with fluorogenic agents at the N-terminal Tyr moiety to their corresponding fluorescent derivatives, subsequently separated on an octadecyl-poly(vinyl alcohol) copolymer gel column, and signal responses are measured fluorimetrically. Both methods permitted the quantification of the synthetic kyotorphin added to the rat brain tissues. The concentration range of kyotorphin-like biogenic peptide was 60-100 pmol/g in the cortex, striatum and hypothalamus tissues.

Animals↗
PubMed1997

Decreased expression of cytokines that induce type 1 helper T cell/interferon-gamma responses in genetically susceptible mice infected with Mycobacterium avium.

Mycobacterium avium is an intracellular microorganism that infects and multiplies within macrophages. Cell-mediated immunity plays an important role in host defense. Two cytokines, interleukin 12 (IL-12) and interferon-gamma-inducing factor (IGIF), produced mainly by macrophages, are critical for the development of type 1 helper T (Th1) cell/interferon-gamma (IFN-gamma) responses and cell-mediated immunity. In this report, by using a mouse model of disseminated M. avium infection, we demonstrate that genetically susceptible BALB/c mice show decreased expression of IL-12 and IGIF in association with a diminished IFN-gamma/Th1 response. Conversely, resistant DBA/2 mice exhibited increased expression of IL-12, IGIF, and IFN-gamma. In both strains of infected mice, the level of IL-4/Th2 response was similar. These results suggest that decreased expression of IL-12 and IGIF leads to a diminished Th1 response without reciprocal enhanced Th2 responses in susceptible mice.

Animals↗
PubMed1997

Monte Carlo simulation of physicochemical processes of liquid water radiolysis. The effects of dissolved oxygen and OH scavenger.

The paper describes developments of the physicochemical part of a computer code system that estimates DNA strand break induction on plasmid pBR322 DNA. In order to test the reliability of the model, we evaluated the dielectric function and the time-dependent yield of chemical species in the presence of OH radical scavenger or dissolved oxygen. Results agree with measurements on the radiolysis of liquid water. When a hybrid model of a liquid inelastic cross-section and a vapour elastic cross-section is used, energy deposition by vibrational excitations is estimated to be approximately 11% of total energy deposition.

Free Radical Scavengers↗
PubMed1997

Expression of C3 and C4 photosynthetic characteristics in the amphibious plant Eleocharis vivipara: structure and analysis of the expression of isogenes for pyruvate, orthophosphate dikinase.

Eleocharis vivipara, a unique leafless amphibious sedge, adopts the C4 mode of photosynthesis under terrestrial conditions and the C3 mode under submerged aquatic conditions. To analyze the molecular basis of these responses to the contrasting environments, we isolated and characterized two full-length cDNAs for a key C4 enzyme, pyruvate, orthophosphate dikinase (PPDK; EC 2.7.9.1). The isogenes for PPDK, designated ppdk1 and ppdk2, were highly homologous to one another but not identical. The PPDK1 protein, deduced from the nucleotide sequence of the cDNA, contained an extra domain at the amino terminus which, presumably, serves as a chloroplast transit peptide, while PPDK2 lacked this extra domain. It seems likely, therefore, that the ppdk1 and ppdk2 genes encode a chloroplastic and a cytosolic PPDK, respectively. Genomic Southern blot analysis revealed the existence of a small family of genes for PPDK in the genome of E. vivipara. Northern blot analysis indicate that both chloroplastic and cytosolic genes for PPDK are expressed simultaneously in the culms, a photosynthetic organ, of E. vivipara and that the pattern of expression of these genes differs between the growth forms.

Amino Acid Sequence↗
PubMed1997

Comparison of stride characteristics in a cantering horse on a flat and inclined treadmill.

The purpose of this study was to determine whether there was any difference in the stride characteristics between cantering on a flat or inclined treadmill. Five 2-year-old Thoroughbred horses were cantered on a treadmill at 3 different velocities and at 3 different slopes. The sequence of speeds at each slope was chosen at random and 16 mm cinefilms at 300 frames/s were taken from a lateral view at a distance of 15 m from the treadmill to record the linear and temporal data. On the slope, stride length, stride duration, stance duration and swing duration did not change. However, midstep length increased significantly and the airborne step length decreased significantly as slope increased from a 3% slope to a 8% slope at 12 m/s. The airborne duration increased significantly from a 0% slope to a 3% slope, and inversely decreased significantly from a 3% slope to a 8% slope. The advanced placement (AP) between trailing hindlimb and leading hindlimb (APTH-LH) and between trailing forelimb and leading forelimb (APTF-LF) and the overlap between LH and TF (LH-TF) tended to decrease and the AP between LH and TF (APLH-TF) and the overlap between TH and LH (TH-LH) inversely tended to increase as the slope increased, though these tendencies were not significant. These findings indicated that in slope locomotion, the stride length might be maintained by sacrificing the length of the airborne period as the workload became more intense.

Animals↗
PubMed1997

Isolation and mapping of a human zinc finger gene (ZNF188) homologous to ZNF187, a serum-response-element binding protein.

From a human pancreas cDNA library we isolated and characterized a novel zinc finger gene encoding a protein homologous to ZNF187, a serum response element-binding protein. The full-length cDNA contained an open reading frame of 1,686 nucleotides encoding a predicted 562-amino-acid peptide that included an ATP-GTP binding site and seven C2H2 zinc finger domains. The consensus sequence of the C2H2 domains (CX2CX3FX5LX2HX3H) is common in the SRE-binding region present in Drosophila Krüppel proteins. An alternatively spliced form of the transcript found in the cDNA library lacked both the ATP-GTP binding site and any C2H2 zinc finger domains. We localized this gene (ZNF188) to chromosome band 7q22.1-->q22.3 by fluorescence in situ hybridization.

Amino Acid Sequence↗
PubMed1997

Chromosome aberrations in bone marrow cells of C3H/He mice at an early stage after whole-body irradiation.

Murine acute myeloid leukemia is characterized by chromosome 2 aberrations, and genesis of the marker chromosome 2 by radiation is suspected to be an initiating event of radiation leukemogenesis. A detailed analysis of the type and frequency of chromosome 2 aberrations in murine bone marrow cells at an early stage after irradiation is provided here. A total of 40 male C3H/He mice was exposed to 137Cs gamma-ray at a dose of 1, 2 or 3 Gy, and sacrificed 24 hours after irradiation. Metaphase samples prepared from bone marrow cells were Q-banded for karyotyping or painted with DNA probes specific to chromosome 2. In 5 mice analyzed by karyotyping, one mouse showed high frequency of the marker aberrations as well as other chromosome 2 aberrations. Chromosome painting analysis for the rest of the mice also detected 3 animals showing significantly high frequencies of chromosome 2 aberrations. Dose-dependence of the frequencies was observed even among those mice that tended to be sensitive. The results indicated that there was a subgroup of mice carrying hypersensitive chromosome 2. The subgroup could be leukemia-sensitive if radiation-induced chromosome aberrations are responsible for an early change in myeloid leukemogenesis.

Animals↗
PubMed1997

Measurement of erythrocyte volumes in splenectomized horses and sham-operated horses at rest and during maximal exercise.

Erythrocyte volumes of thoroughbred horses were measured. The volumes of splenectomized horses and sham-operated horses 2 hr after injection of 50Cr-tagged erythrocytes (at rest) and during maximal exercise were measured using the non-radioactive isotope 50Cr. Because splenic erythrocytes are released into circulation during exercise, it was estimated that the erythrocyte volumes of the sham-operated horses during maximal exercise are larger than those of the horses at rest. However, the erythrocyte volumes of the sham-operated horses at rest were about equal to those during maximal exercise. In the splenectomized horses, furthermore, erythrocyte volumes at rest and those at exercise were nearly equal. From these results, blood stored in the equine spleen is gradually mixed with circulating blood, and it was clarified that the phenomenon was completed within 2 hr. Although it is basically impossible to measure the circulating erythrocyte volume at rest using the erythrocyte tagged method, we observed that it is possible to measure the total erythrocyte volume using the 50Cr method. Also, the plasma volumes of the splenectomized horses during maximal exercise were found to be slightly smaller than those at rest. On the other hand, in the sham-operated horses, the plasma was decreased by a large quantity after maximal exercise. Therefore, it was suggested that the spleen participates in the phenomenon involving the disappearance of plasma from circulation due to exercise.

Animals↗
PubMed1997

The embryonic and fetal effects in ICR mice irradiated in the various stages of the preimplantation period.

Pregnant ICR mice were irradiated with 0.1-2.5 Gy 137Cs gamma rays at a dose rate of 0.2 Gy/min at 2, 48, 72 or 96 h postconception. In the mice irradiated during these stages of preimplantation, embryonic/fetal mortalities, incidence of external gross malformations, fetal body weight and sex ratio were observed at day 18 of gestation. There were significant increases in death in the preimplantation period compared to control levels after exposure to at least 0.25 Gy at 2 and 72 h postconception and 0.5 Gy at 96 h postconception. In contrast, a dose of 1.5 Gy was required at 48 h postconception. The frequency of embryonic death was analyzed using a logistic regression for comparing among stages. These analyses demonstrated that the regression slopes were significantly positive for groups in all stages and increased with decreasing time after conception. Furthermore, the regression analyses suggested that the most sensitive stage for preimplantation death and embryonic death was 2 h postconception, when embryos consisted of one cell. Many types of external gross malformations, such as exencephaly, cleft palate and anophthalmia, were observed even in the mice irradiated with 0.1 Gy at 2, 72 and 96 h postconception. In the same manner as embryonic mortality, the regression analyses suggested that the susceptibility of the mice irradiated at 2, 72 and 96 h postconception during preimplantation to external malformations was higher than that of the mice irradiated at 8 or 11 days of gestation, which is the period of organogenesis, and that the most sensitive stage for external malformations was 2 h postconception. However, no malformations were observed in the mice irradiated at 48 h postconception when the embryos were precompacted with four to eight cells.

Abnormalities, Radiation-Induced↗
PubMed1997

"Honeymoon psychosis" in Japanese tourists to Hawaii.

Although Japanese tourists in Hawaii are infrequently treated for acute psychiatric emergencies, we observed several cases among Japanese honeymooners. To investigate this phenomenon, we retrospectively and prospectively collected such cases of honeymooners. Sixteen cases of acute psychiatric disturbance in Japanese honeymooners in Hawaii are described. This phenomenon occurs more frequently than in other Japanese tourists or non-Japanese honeymooners. The tradition of arranged marriage and other cultural factors may be associated with the potential for "honeymoon psychosis."

Acute Disease↗