Biomedical subjects

Takayuki Sasaki

Publications and source records attributed to Takayuki Sasaki.

At least 19 recordsLinked to original sources

PubMed2006

Sequence upstream of the wheat (Triticum aestivum L.) ALMT1 gene and its relationship to aluminum resistance.

Aluminum (Al) resistance in wheat relies on the Al-activated malate efflux from root apices, which appears to be controlled by an Al-activated anion transporter encoded by the ALMT1 gene on chromosome 4DL. Genomic regions upstream and downstream of ALMT1 in 69 wheat lines were characterized to identify patterns that might influence ALMT1 expression. The first 1,000 bp downstream of ALMT1 was conserved among the lines examined apart from the presence of a transposon-like sequence which did not correlate with Al resistance. In contrast, the first 1,000 bp upstream of the ALMT1 coding region was more variable and six different patterns could be discerned (types I-VI). Type I had the simplest structure, while the others had blocks of sequence that were duplicated or triplicated in different arrangements. A pattern emerged among the lines of non-Japanese origin such that the number of repeats in this upstream region was positively correlated with the levels of ALMT1 expression and Al resistance. In contrast, many of the Japanese lines exhibited a large variation in ALMT1 expression and Al resistance despite possessing the same type of upstream region. Although ALMT1 expression was also poorly correlated with Al-activated malate efflux in the Japanese lines, a strong correlation between malate efflux and Al resistance suggested that malate efflux was still the primary mechanism for Al resistance, and that additional genes are involved in the post-transcriptional regulation of ALMT1 function.

Aluminum↗

PubMed2006

AtALMT1, which encodes a malate transporter, is identified as one of several genes critical for aluminum tolerance in Arabidopsis.

Aluminum (Al) tolerance in Arabidopsis is a genetically complex trait, yet it is mediated by a single physiological mechanism based on Al-activated root malate efflux. We investigated a possible molecular determinant for Al tolerance involving a homolog of the wheat Al-activated malate transporter, ALMT1. This gene, named AtALMT1 (At1g08430), was the best candidate from the 14-member AtALMT family to be involved with Al tolerance based on expression patterns and genomic location. Physiological analysis of a transferred DNA knockout mutant for AtALMT1 as well as electrophysiological examination of the protein expressed in Xenopus oocytes showed that AtALMT1 is critical for Arabidopsis Al tolerance and encodes the Al-activated root malate efflux transporter associated with tolerance. However, gene expression and sequence analysis of AtALMT1 alleles from tolerant Columbia (Col), sensitive Landsberg erecta (Ler), and other ecotypes that varied in Al tolerance suggested that variation observed at AtALMT1 is not correlated with the differences observed in Al tolerance among these ecotypes. Genetic complementation experiments indicated that the Ler allele of AtALMT1 is equally effective as the Col allele in conferring Al tolerance and Al-activated malate release. Finally, fine-scale mapping of a quantitative trait locus (QTL) for Al tolerance on chromosome 1 indicated that AtALMT1 is located proximal to this QTL. These results indicate that AtALMT1 is an essential factor for Al tolerance in Arabidopsis but does not represent the major Al tolerance QTL also found on chromosome 1.

Aluminum↗

PubMed2006

How representations of the parental marriage predict marital emotional attunement during the transition to parenthood.

Emotional attunement (i.e., couples' dyadic emotional connectedness and responsiveness) was examined in 86 couples across the transition to parenthood. After controlling for prenatal emotional attunement and verbal ability, the authors found that prenatal assessments of husbands' and wives' representations of their parents' marriage (i.e., content and insightfulness) predicted emotional attunement between partners 24 months postpartum. There was a trend for husbands and a statistically significant relationship for wives who insightfully recalled disharmonious content to show greater residualized postnatal emotional attunement compared with other husbands and wives, suggesting that anticipating marital problems following the transition to parenthood may increase attention to maintaining the marriage. In contrast, wives who recalled disharmonious content with low insight showed the lowest residualized postnatal scores for emotional attunement.

Adaptation, Psychological↗

PubMed2006

Genetically engineered Bifidobacterium longum for tumor-targeting enzyme-prodrug therapy of autochthonous mammary tumors in rats.

A fundamental obstacle in systemic therapy for cancer patients is the specific targeting of therapy directly to solid tumors. A strain of the domestic bacterium Bifidobacterium longum, which is non-pathogenic and anaerobic, showed selective localization to and proliferation within solid tumors after systemic application. Here, we propose a novel approach to cancer gene therapy in which anaerobic and non-pathogenic bacteria of the genus B. longum are used to achieve tumor-specific gene delivery and enzyme-prodrug therapy. We constructed a plasmid, pBLES100-S-eCD, which included eCD. Transfected B. longum produced CD in hypoxic tumors and achieved tumor site-specific conversion of 5-FC to 5-FU. Furthermore, we demonstrated antitumor efficacy in rat bearing autochthonous mammary tumors injected with the transfected B. longum directly or intravenously. This method was confirmed to be effective for enzyme-prodrug therapy not only by intratumoral injection but also by systemic administration. To estimate the toxicity of this bacterial vector, the systemic immunogenicity was evaluated by ASA reaction and the anaphylactic activity of IgG was evaluated by PCA reaction in guinea pigs. In the ASA reaction, no anaphylaxis symptoms were observed in any immunized guinea pigs injected with transfected B. longum. In the PCA reaction, B. longum/S-eCD specific-PCA-induced antibody was not detected. Thus, we proposed that anaerobic bacteria of the genus B. longum were an attractive and safe tumor-targeting vector and transfected B. longum was a potential anticancer agent that could effectively and specifically treat solid tumors.

Animals↗

PubMed2006

Clinical pharmacokinetics of mycophenolate mofetil in Japanese renal transplant recipients: A retrospective cohort study in a single center.

Mycophenolate mofetil (MMF), a morpholinoethyl ester of mycophenolic acid (MPA), is currently widely used in organ transplantation as an immunosuppressant. The usefulness of therapeutic drug monitoring (TDM) of MPA after MMF dosing is not clear in Japanese renal transplant patients. In this study, to obtain more information for TDM of MPA, the association between MPA pharmacokinetic characteristics and the development of the side effects, and the effect of other concomitant immunosupressants such as cyclospoline A (CyA), tacrolimus (FK) and predonisolone (PSL) on MPA pharmacokinetics were investigated in detail. Moreover, the effects of enterohepatic recirculation (EHRA) on pharmacokinetic characteristics of MPA and the development of the side effects were also investigated. AUC(MPA)(0-9) with FK medication was 1.3-1.9 times higher than that with CyA medication, and the contribution to the plasma level of MPA of FK might be smaller than that of CyA, because EHRA inhibition by CyA was 2 times greater than that by FK. AUC(MPA)(0-9) was not influenced by PSL. The association between AUC(MPA)(0-9) and the development of the side effects was not observed; however, the development of side effects (leukopenia and diarrhea) in the EHRA group was 2 times higher than that in the non-EHRA group. These results suggested that TDM for MPA after MMF dosing was desirable in Japanease transplant patients. However, though not frequently, AUC obtained by multiple blood sampling after MMF dosing was needed. In addition, EHRA has led to increasing interest in MMF medication.

Adolescent↗

PubMed2005

Citrate secretion coupled with the modulation of soybean root tip under aluminum stress. Up-regulation of transcription, translation, and threonine-oriented phosphorylation of plasma membrane H+-ATPase.

The aluminum (Al)-induced secretion of citrate has been regarded as an important mechanism for Al resistance in soybean (Glycine max). However, the mechanism of how Al induces citrate secretion remains unclear. In this study, we investigated the regulatory role of plasma membrane H+-ATPase on the Al-induced secretion of citrate from soybean roots. Experiments performed with plants grown in full nutrient solution showed that Al-induced activity of plasma membrane H+-ATPase paralleled secretion of citrate. Vanadate and fusicoccin, an inhibitor and an activator, respectively, of plasma membrane H+-ATPase, exerted inhibitory and stimulatory effects on the Al-induced secretion of citrate. Higher activity of plasma membrane H+-ATPase coincided with more citrate secretion in Al-resistant than Al-sensitive soybean cultivars. These results suggested that the effects of Al stress on citrate secretion were mediated via modulation of the activity of plasma membrane H+-ATPase. The relationship between the Al-induced secretion of citrate and the activity of plasma membrane H+-ATPase was further demonstrated by analysis of plasma membrane H+-ATPase transgenic Arabidopsis (Arabidopsis thaliana). When plants were grown on Murashige and Skoog medium containing 30 microM Al (9.1 microM Al3+ activity), transgenic plants exuded more citrate compared with wild-type Arabidopsis. Results from real-time reverse transcription-PCR and immunodetection analysis indicated that the increase of plasma membrane H+-ATPase activity by Al is caused by transcriptional and translational regulation. Furthermore, plasma membrane H+-ATPase activity and expression were higher in an Al-resistant cultivar than in an Al-sensitive cultivar. Al activated the threonine-oriented phosphorylation of plasma membrane H+-ATPase in a dose- and time-dependent manner. Taken together, our results demonstrated that up-regulation of plasma membrane H+-ATPase activity was associated with the secretion of citrate from soybean roots.

Aluminum↗

PubMed2005

Evidence for the plasma membrane localization of Al-activated malate transporter (ALMT1).

Aluminum (Al)-activated malate transporter (ALMT1) was recently identified from wheat (Triticum aestivum). Heterologous expression of ALMT1 led to higher malate exudation that is associated with enhanced Al tolerance in transgenic plants. Here, we show the first direct evidence that ALMT1 is localized in the plasma membrane of Al-tolerant wheat. Phase partitioning experiments showed that this transporter was associated with the plasma membrane fraction. ALMT1 was detected in an Al-tolerant wheat line even without Al treatments. Analysis of transient expression of ALMT1::green fluorescent protein (GFP) in onion and tobacco cells further confirmed this ALMT1 localization.

Aluminum↗

PubMed2005

Quantitative trait loci mapping for intracellular calcium in spontaneously hypertensive rats.

BACKGROUND: Increased intracellular calcium ([Ca2+]i) in platelets is also proposed as an intermediate phenotype for hypertension in spontaneously hypertensive rats (SHR). Increased [Ca2+]i in platelets is hypothesized to contribute to atherothrombotic events. Platelet hyperactivity is frequently associated with cardiovascular disease. METHODS: In a genome scan, we performed the quantitative trait loci (QTL) mapping for [Ca2+]i in back-crossed rats derived from SHR and normotensive Fischer 344 rats, which demonstrated a single major QTL for hypertension on chromosome 1. Thrombin-stimulated [Ca2+]i in Ca2+-free and in Ca2+-containing buffers was measured in platelets using the Fura-2 method. RESULTS: Among the parental strains, systolic blood pressure and thrombin-stimulated [Ca2+]i were significantly greater in SHR than in Fischer 344 and F1 rats. The sarco(endo)plasmic reticulum Ca2+-dependent ATPase II gene locus (Serca2) between D12Mgh5 and D12Mgh6 showed the significant linkage for thrombin-stimulated [Ca2+]i in Ca2+-free and Ca2+-containing buffers. The peak logarithm of the odds scores were 3.6 and 3.3, respectively. These QTL explained 19.8% and 17.4% of the total variances, respectively. D3Mit13 and DXMgh1 showed suggestive linkage for thrombin-stimulated [Ca2+]i in Ca2+-free and in Ca2+-containing buffers, respectively. The peak logarithm of the odds scores were 2.6 and 2.1, respectively. CONCLUSIONS: A significant QTL for [Ca2+]i was mapped near Serca2 on chromosome 12, and suggestive QTL were identified near D3Mit13 and DXMgh1 in a genome scan. Genetic abnormalites in platelet [Ca2+]i may contribute to cardiovascular disease via platelet hyperactivity, independent of blood pressure elevation.

Animals↗

PubMed2005

Physiological and genetic analyses of aluminium tolerance in rice, focusing on root growth during germination.

Aluminium (Al) ion limits root growth of plants in acidic soils, and rice exhibits the highest level of Al-tolerance among graminous crops. To elucidate Al-tolerance mechanisms in rice, response to Al was compared between rice (Oryza sativa L., cv. Nipponbare) and wheat (Triticum aestivum L., cv. ET8), focusing on seminal root growth at seedling stage and germination stage. At seedling stage, rice and wheat were similarly sensitive to Al in both dose- and time-dependent manner during a 24-h Al exposure. On the contrary, at germination stage, rice was more tolerant to Al than wheat, and wheat roots displayed the loss of plasma membrane integrity more extensively than rice. A rice mutant exhibiting Al hypersensitivity at germination stage was obtained by screening 42,840 R2 progeny derived from the regenerated R0 plants of Nipponbare and thereafter confirmation of the mutant phenotype in R3 progeny. At germination stage, root growth of the mutant was strongly inhibited in the presence of Al but not in the absence of Al. However, at seedling stage, root growth of the mutant and wild type was similarly tolerant to Al. Taken together, we conclude that rice possesses Al-tolerant function that is under genetic control and specifically operates for root growth at germination stage, making rice more tolerant to Al than wheat.

Adaptation, Physiological↗

PubMed2005

Molecular characterization and mapping of ALMT1, the aluminium-tolerance gene of bread wheat (Triticum aestivum L.).

The major aluminum (Al) tolerance gene in wheat ALMT1 confers. An Al-activated efflux of malate from root apices. We determined the genomic structure of the ALMT1 gene and found it consists of 6 exons interrupted by 5 introns. Sequencing a range of wheat genotypes identified 3 alleles for ALMT1, 1 of which was identical to the ALMT1 gene from an Aegilops tauschii accession. The ALMT1 gene was mapped to chromosome 4DL using 'Chinese Spring' deletion lines, and loss of ALMT1 coincided with the loss of both Al tolerance and Al-activated malate efflux. Aluminium tolerance in each of 5 different doubled-haploid populations was found to be conditioned by a single major gene. When ALMT1 was polymorphic between the parental lines, QTL and linkage analyses indicated that ALMT1 mapped to chromosome 4DL and cosegregated with Al tolerance. In 2 populations examined, Al tolerance also segregated with a greater capacity for Al-activated malate efflux. Aluminium tolerance was not associated with a particular coding allele for ALMT1, but was significantly correlated with the relative level of ALMT1 expression. These findings suggest that the Al tolerance in a diverse range of wheat genotypes is primarily conditioned by ALMT1.

Alleles↗

PubMed2005

Divergent effects of unilateral and subtotal nephrectomy on insulin sensitivity in rats.

OBJECTIVES: Insulin resistance is associated with chronic renal failure, which may amplify its cardiovascular pathologic manifestations. We previously showed the presence of insulin resistance in mild renal insufficiency due to chronic glomerulonephritis. These observations may be explained by a decrease in insulin sensitivity due to renal dysfunction. The aim of the present study was to evaluate the effects of unilateral and subtotal nephrectomy on insulin sensitivity. METHODS: Unilateral heminephrectomy and five-sixths nephrectomy (5/6Nx) were performed in male Sprague-Dawley rats, measuring steady-state plasma glucose (SSPG) during the insulin suppression test. RESULTS: The glomerular filtration rate (GFR) decreased significantly from sham-operated rats, to unilateral heminephrectomy group, to 5/6Nx rats. SSPG was unexpectedly lower in the unilateral heminephrectomy group than in controls, suggesting that unilateral heminephrectomy increased the sensitivity to insulin despite a mild decrease in renal function. However, when the analysis was limited to the 5/6Nx group, SSPG was inversely correlated with GFR (r = -0.65, p < 0.05). When renal failure caused by 5/6Nx had reached end stage, the rats became insulin resistant, despite a profound reduction in renal mass. CONCLUSION: It is suggested that unilateral heminephrectomy reduced GFR and increased the sensitivity to insulin. When rats became uremic, insulin sensitivity decreased, even, in 5/6Nx.

Animals↗

PubMed2004

Engineering high-level aluminum tolerance in barley with the ALMT1 gene.

Acidity is a serious limitation to plant production on many of the world's agricultural soils. Toxic aluminium (Al) cations solubilized by the acidity rapidly inhibit root growth and limit subsequent uptake of water and nutrients. Recent work has shown that the ALMT1 gene of wheat (Triticum aestivum) encodes a malate transporter that is associated with malate efflux and Al tolerance. We generated transgenic barley (Hordeum vulgare) plants expressing ALMT1 and assessed their ability to exude malate and withstand Al stress. ALMT1 expression in barley conferred an Al-activated efflux of malate with properties similar to those of Al-tolerant wheat. The transgenic barley showed a high level of Al tolerance when grown in both hydroponic culture and on acid soils. These findings provide additional evidence that ALMT1 is a major Al-tolerance gene and demonstrate its ability to confer effective tolerance to acid soils through a transgenic approach in an important crop species.

Aluminum↗

PubMed2004

Separation of radionuclides in a multitracer prepared by thermal neutron fission of 235U.

In response to the needs of research groups in Japan, a chemical separation procedure was developed for isolating specific radioactive isotopes from a multitracer prepared by the reaction of 235U fission induced by thermal neutrons. This efficient technique is based on solvent extraction and separates the multitracer isotopes into six groups. It is intended to be used in an automated rapid extraction system.

Journal Article↗

PubMed2004

Time-shrinking: the process of unilateral temporal assimilation.

Our previous research on auditory time perception showed that the duration of empty time intervals shorter than about 250 ms can be underestimated hugely if they are immediately preceded by shorter time intervals. We named this illusion 'time-shrinking' (TS). This study comprises four experiments in which the preceding interval, t1, was followed by a standard interval, t2. When t1 < or = 200 ms, and t1 < or = t2, the underestimation of t2 came into view clearly. The absolute difference between t2 and t1 was the crucial factor for the illusion to appear. The underestimation increased when t2 increased from t1 to t1 + 65 ms, stayed at about 45 ms when t2 was between t1 + 65 ms and t1 + 95 ms, and disappeared suddenly when t2 exceeded t1 + 95 ms. This pattern of results was observed across all values of t1 < or = 200 ms. A model was fit to the data to elucidate the underlying process of the illusion. The model states that the perceived duration difference between t1 and t2 is reduced by cutting mental processing time for t2; in other words, that t2 assimilates to t1.

Acoustic Stimulation↗

PubMed2004

A wheat gene encoding an aluminum-activated malate transporter.

The major constraint to plant growth in acid soils is the presence of toxic aluminum (Al) cations, which inhibit root elongation. The enhanced Al tolerance exhibited by some cultivars of wheat is associated with the Al-dependent efflux of malate from root apices. Malate forms a stable complex with Al that is harmless to plants and, therefore, this efflux of malate forms the basis of a hypothesis to explain Al tolerance in wheat. Here, we report on the cloning of a wheat gene, ALMT1 (aluminum-activated malate transporter), that co-segregates with Al tolerance in F2 and F3 populations derived from crosses between near-isogenic wheat lines that differ in Al tolerance. The ALMT1 gene encodes a membrane protein, which is constitutively expressed in the root apices of the Al-tolerant line at greater levels than in the near-isogenic but Al-sensitive line. Heterologous expression of ALMT1 in Xenopus oocytes, rice and cultured tobacco cells conferred an Al-activated malate efflux. Additionally, ALMT1 increased the tolerance of tobacco cells to Al treatment. These findings demonstrate that ALMT1 encodes an Al-activated malate transporter that is capable of conferring Al tolerance to plant cells.

Adaptation, Physiological↗

PubMed2004

Perceptual organization of onsets and offsets of sounds.

Several illusory phenomena in auditory perception are accounted for by using the event construction model presented by Nakajima et al. (2000) in order to explain the gap transfer illusion. This model assumes that onsets and offsets of sounds are detected perceptually as if they were independent auditory elements. They are connected to one another according to the proximity principle to constitute auditory events. This model seems to contribute to a general cross-modal theory of perception where the idea of edge integration plays an important role. Potential directions in which we can connect the present paradigm with speech perception are indicated, and possibilities to improve artificial auditory environments are suggested.

Auditory Perception↗

PubMed2002

The activity for the induction of the sperm acrosome reaction localises in the outer layers and exists in the high-molecular-weight components of the egg-jelly of the newt, Cynops pyrrhogaster.

Localisation of the acrosome reaction inducing activity in egg-jelly was examined in the newt, Cynops pyrrhogaster. The jelly has six layers: the J0, J1, J2, J3, J4 and st layers. Jelly was mechanically dissected and placed on a Millipore filter. When sperm were added from the outer surface side of the jelly, most of them exhibited the acrosome reaction after passing through the jelly. When egg-jelly was divided into four layers, strong activity for the induction of acrosome reaction was detected in the outer layers, J4+st. These findings suggest that the acrosome reaction is induced by a substance in the outer layers of the egg-jelly. Among jelly components separated by SDS-PAGE, a fraction of more than 500 kDa in molecular weight induced the acrosome reaction. Wheat germ agglutinin (WGA), Griffonia simplicifoliar agglutinin 1 (GS-1), Maclura pomifera agglutinin (MPA) and Arachis hypogaea agglutinin (PNA) inhibited the induction of the acrosome reaction by jelly extract, and WGA did so in a dose-dependent manner. Those lectins precipitated some molecules of over 500 kDa. These results suggest that the acrosome reaction is induced by the high molecular-weight components of egg-jelly in C. pyrrhogaster.

Acrosome Reaction↗

PubMed2002

A gene encoding multidrug resistance (MDR)-like protein is induced by aluminum and inhibitors of calcium flux in wheat.

A cDNA clone exclusively induced by aluminum (Al) was isolated from root apices of wheat (Triticum aestivum L.) by the differential display method. The predicted amino acid sequence exhibited homology to the multidrug resistance (MDR) proteins that is known as a member of the ATP-binding cassette (ABC) protein superfamily. Thus this gene was named TaMDR1 (Triticum aestivum MDR). TaMDR1 was induced as a function of Al concentration in the range from 5 to 50 microM, which is in the range of Al content in natural acid soil environment. The concentration required for the induction was lower in the Al-sensitive cultivar than in the Al-tolerant cultivar, indicating that the accumulation of TaMDR1 mRNA was associated with the events caused by Al toxicity rather than Al tolerance. TaMDR1 was significantly induced by the exposure to lanthanum, gadolinium and ruthenium red, which are known as inhibitors of calcium channels. Furthermore, decreasing of calcium ion in growth medium caused stimulation of the gene expression. These results suggested that the induction of TaMDR1 is caused by the breaking of calcium homeostasis which occurred at early stage of Al toxicity.

ATP Binding Cassette Transporter, Subfamily B↗