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Biomedical subjects

M Tasaka

Publications and source records attributed to M Tasaka.

At least 19 recordsLinked to original sources
PubMed2004

[Partial anomalous pulmonary venous drainage to the high superior vena cava; repair by direct anastomosis between the superior vena cava and the right atrial appendage; report of a case].

A 10-year-old boy with partial anomalous pulmonary venous connection to the high superior vena cava (SVC) underwent surgical repair by Williams method. The SVC was divided above the orifice of the anomalous pulmonary vein. The proximal end of the SVC was closed and the distal end of the SVC was anastomosed to the right atrial appendage (RAA). The anomalous pulmonary vein was rerouted to the left atrium via the SVC and the surgically enlarged central type atrial septal defect (ASD). The postoperative course was uneventful except transient sinus bradycardia and catheter study showed no stenosis of the SVC and the RAA.

Anastomosis, Surgical↗
PubMed2001

Genetic regulation of gravitropism in higher plants.

Gravitropism is a classical subject in plant physiology. However, the molecular mechanisms that regulate gravitropism are unknown. Recently, many gravitropic mutants have been isolated from Arabidopsis thaliana and several genes for gravitropism have been cloned and characterized. These studies have shown that (1) the endodermis is essential for shoot gravitropism and (2) an auxin transport system and signaling pathway are necessary for gravitropism. Recent studies in Arabidopsis are reviewed and genetic regulation of gravitropism in this organism is discussed.

Arabidopsis↗
PubMed2001

An approach to metal-assisted DNA base pairing: novel beta-C-nucleosides with a 2-aminophenol or a catechol as the nucleobase.

The metal-chelating beta-C-nucleoside having a phenylenediamine moiety as the nucleobase was previously found to form a stable 2:1 complex with a Pd(2+) ion in aqueous media, where hydrogen bonding is replaced by metal coordination in the base pairing, thereby creating a novel hybridization motif in duplex DNA. In this regard, we have further designed two types of artificial beta-C-nucleosides possessing a metal-chelating site (a 2-aminophenol or a catechol) as the nucleobase moiety. These artificial nucleosides are directed toward controlling the net charges of the metal-assisted base pairs. This paper describes convenient syntheses of the artificial nucleosides bearing a 2-aminophenol or a catechol moiety. Each nucleoside was directly synthesized through 2'-deoxy derivative via a Friedel-Crafts coupling reaction as the key step between the aromatic ring and ribose moiety, whereas the nucleoside having a phenylenediamine moiety was prepared in rather longer steps through an RNA type intermediate followed by the removal of 2'-hydroxyl group.

Aminophenols↗
PubMed2001

From central-peripheral to adaxial-abaxial.

Higher plants are constructed of three organs--the stem, the root and the leaf. The stem and the root have two axes, apical-basal and central-peripheral, which cross orthogonally. Leaves develop from the shoot apical meristem as lateral organs that have three different axes, apical-basal, adaxial-abaxial and right-left. Recent data point to the possibility that the adaxial-abaxial axis in the leaf is formed from the central-peripheral axis in the stem.

Magnoliopsida↗
PubMed2001

The CUP-SHAPED COTYLEDON1 gene of Arabidopsis regulates shoot apical meristem formation.

In higher plants, molecular mechanisms regulating shoot apical meristem (SAM) formation and organ separation are largely unknown. The CUC1 (CUP-SHAPED COTYLEDON1) and CUC2 are functionally redundant genes that are involved in these processes. We cloned the CUC1 gene by a map-based approach, and found that it encodes a NAC-domain protein highly homologous to CUC2. CUC1 mRNA was detected in the presumptive SAM during embryogenesis, and at the boundaries between floral organ primordia. Surprisingly, overexpression of CUC1 was sufficient to induce adventitious shoots on the adaxial surface of cotyledons. Expression analyses in the overexpressor and in loss-of-function mutants suggest that CUC1 acts upstream of the SHOOT MERISTEMLESS gene.

Amino Acid Sequence↗
PubMed2000

A critical role of sterols in embryonic patterning and meristem programming revealed by the fackel mutants of Arabidopsis thaliana.

Here we report a novel Arabidopsis dwarf mutant, fackel-J79, whose adult morphology resembles that of brassinosteroid-deficient mutants but also displays distorted embryos, supernumerary cotyledons, multiple shoot meristems, and stunted roots. We cloned the FACKEL gene and found that it encodes a protein with sequence similarity to both the human sterol reductase family and yeast C-14 sterol reductase and is preferentially expressed in actively growing cells. Biochemical analysis indicates that the fk-J79 mutation results in deficient C-14 sterol reductase activity, abnormal sterol composition, and reduction of brassinosteroids (BRs). Unlike other BR-deficient mutants, the defect of hypocotyl elongation in fk-J79 cannot be corrected by exogenous BRs. The unique phenotypes and sterol composition in fk-J79 indicate crucial roles of sterol regulation and signaling in cell division and cell expansion in embryonic and post-embryonic development in plants.

Alleles↗
PubMed2000

Involvement of CUP-SHAPED COTYLEDON genes in gynoecium and ovule development in Arabidopsis thaliana.

When mutations in CUP-SHAPED COTYLEDON1 (CUC1) and CUC2 are combined, severe defects involving fusion of sepals and of stamens occur in Arabidopsis flowers. In addition, septa of gynoecia do not fuse along the length of the ovaries and many ovules have their growth arrested. CUC2 is expressed at the tips of septal primordia during gynoecium development and at the boundary between nucellus and chalaza during ovule development. These expression patterns are partially consistent with the phenotype of the mutant gynoecium. CUC2 mRNA is also shown to be expressed at the boundaries between meristems and organ primordia during both the vegetative and reproductive phases. This expression pattern indicates that CUC2 is generally involved in organ separation in shoot and floral meristems.

Arabidopsis↗
PubMed1999

Complementation of plant mutants with large genomic DNA fragments by a transformation-competent artificial chromosome vector accelerates positional cloning.

To accelerate gene isolation from plants by positional cloning, vector systems suitable for both chromosome walking and genetic complementation are highly desirable. Therefore, we developed a transformation-competent artificial chromosome (TAC) vector, pYLTAC7, that can accept and maintain large genomic DNA fragments stably in both Escherichia coli and Agrobacterium tumefaciens. Furthermore, it has the cis sequences required for Agrobacterium-mediated gene transfer into plants. We cloned large genomic DNA fragments of Arabidopsis thaliana into the vector and showed that most of the DNA fragments were maintained stably. Several TAC clones carrying 40- to 80-kb genomic DNA fragments were transferred back into Arabidopsis with high efficiency and shown to be inherited faithfully among the progeny. Furthermore, we demonstrated the practical utility of this vector system for positional cloning in Arabidopsis. A TAC contig was constructed in the region of the SGR1 locus, and individual clones with ca. 80-kb inserts were tested for their ability to complement the gravitropic defects of a homozygous mutant line. Successful complementation enabled the physical location of SGR1 to be delimited with high precision and confidence.

Agrobacterium tumefaciens↗
PubMed1999

The endodermis and shoot gravitropism

Shoots and roots of higher plants exhibit negative and positive gravitropism, respectively. A variety of gravitropic mutants have recently been isolated from Arabidopsis, the characterization of which demonstrates that the molecular mechanisms of the gravitropic responses in roots, hypocotyls and inflorescence stems are different. The cytological and molecular analysis of two mutants, shoot gravitropism 1 (sgrl), which is allelic to scarecrow (scr), and sgr7, which is allelic to short-root(shr), indicate that the endodermis is the site of gravity perception in shoots. These data suggest a new model for shoot gravitropism.

Arabidopsis↗
PubMed1999

Gravity perception and gravitropic response of inflorescence stems in Arabidopsis thaliana.

Shoots of higher plants exhibit negative gravitropism. However, little is known about the site of gravity perception in shoots and the molecular mechanisms of shoot gravitropic responses. Our recent analysis using shoot gravitropism 1(sgr1)/scarecrow(scr) and sgr7/short-root (shr) mutants in Arabidopsis thaliana indicated that the endodermis is essential for shoot gravitropism and strongly suggested that the endodermis functions as the gravity-sensing cell layer in dicotyledonous plant shoots. In this paper, we present our recent analysis and model of gravity perception and gravitropic response of inflorescence stems in Arabidopsis thaliana.

Arabidopsis↗
PubMed1999

Artificial DNAs with metal-assisted base pairs.

Two types of artificial beta-C-nucleosides, 2 and 3, were newly synthesized, which possess a metal chelating site (2-aminophenol and catechol, respectively) at the nucleobase moiety. These nucleosides are expected to form metal-assisted base pairs in oligonucleotides and thereby to control high-order structures and functions of DNAs.

Aminophenols↗
PubMed1999

Transgenic tobacco over-expressing a homeobox gene shows a developmental interaction between leaf morphogenesis and phyllotaxy.

The tobacco gene, NTH1, encodes a polypeptide of 326 amino acids and is a member of the class1 KN1-type family of homeobox genes. Expression of NTH1 has mainly been observed in vegetative and reproductive shoot apices, not observed in roots or expanded leaves. Over-expression of NTH1 in transgenic plants caused abnormal leaf morphology, consisting of wrinkling and curvature. Interestingly, the direction of leaf curvature tended to be conserved among almost all of the leaves in any given transformant. In transgenic plants exhibiting clockwise or anticlockwise phyllotaxy, leaves curved to the right or left, respectively, when looking from the shoot apex toward the base. Micro-surgical experiments demonstrated that the presence of the shoot apex is necessary for the development of leaf curvature, indicating that the order of formation of leaves on the stem (the generative spiral) affects leaf development. We found a correlation between the severity of leaf curvature and the value of the plastochron ratio, a parameter of phyllotaxy. Transformants with more severe phenotypes had larger plastochron ratios. From these findings, we discuss the possibility that an increase in the plastochron ratio, caused by over-expression of NTH1 in the shoot apex, may be involved in leaf curvature.

Amino Acid Sequence↗
PubMed1999

The PINHEAD/ZWILLE gene acts pleiotropically in Arabidopsis development and has overlapping functions with the ARGONAUTE1 gene.

Several lines of evidence indicate that the adaxial leaf domain possesses a unique competence to form shoot apical meristems. Factors required for this competence are expected to cause a defect in shoot apical meristem formation when inactivated and to be expressed or active preferentially in the adaxial leaf domain. PINHEAD, a member of a family of proteins that includes the translation factor eIF2C, is required for reliable formation of primary and axillary shoot apical meristems. In addition to high-level expression in the vasculature, we find that low-level PINHEAD expression defines a novel domain of positional identity in the plant. This domain consists of adaxial leaf primordia and the meristem. These findings suggest that the PINHEAD gene product may be a component of a hypothetical meristem forming competence factor. We also describe defects in floral organ number and shape, as well as aberrant embryo and ovule development associated with pinhead mutants, thus elaborating on the role of PINHEAD in Arabidopsis development. In addition, we find that embryos doubly mutant for PINHEAD and ARGONAUTE1, a related, ubiquitously expressed family member, fail to progress to bilateral symmetry and do not accumulate the SHOOT MERISTEMLESS protein. Therefore PINHEAD and ARGONAUTE1 together act to allow wild-type growth and gene expression patterns during embryogenesis.

Alleles↗
PubMed1999

Shoot apical meristem and cotyledon formation during Arabidopsis embryogenesis: interaction among the CUP-SHAPED COTYLEDON and SHOOT MERISTEMLESS genes.

The shoot apical meristem and cotyledons of higher plants are established during embryogenesis in the apex. Redundant CUP-SHAPED COTYLEDON 1 (CUC1) and CUC2 as well as SHOOT MERISTEMLESS (STM) of Arabidopsis are required for shoot apical meristem formation and cotyledon separation. To elucidate how the apical region of the embryo is established, we investigated genetic interactions among CUC1, CUC2 and STM, as well as the expression patterns of CUC2 and STM mRNA. Expression of these genes marked the incipient shoot apical meristem as well as the boundaries of cotyledon primordia, consistent with their roles for shoot apical meristem formation and cotyledon separation. Genetic and expression analyses indicate that CUC1 and CUC2 are redundantly required for expression of STM to form the shoot apical meristem, and that STM is required for proper spatial expression of CUC2 to separate cotyledons. A model for pattern formation in the apical region of the Arabidopsis embryo is presented.

Arabidopsis↗
PubMed1998

Genetic evidence that the endodermis is essential for shoot gravitropism in Arabidopsis thaliana.

Shoots of higher plants exhibit negative gravitropism. However, little is known about the mechanism or site of gravity perception in shoots. We have identified two loci that are essential for normal shoot gravitropism in Arabidopsis thaliana. Genetic analysis demonstrated that the shoot gravitropism mutants sgr1 and sgr7 are allelic to the radial pattern mutants, scr and shr, respectively. Characterization of the aerial phenotype of these mutants revealed that the primary defect is the absence of a normal endodermis in hypocotyls and influorescence stems. This indicates that the endodermis is essential for shoot gravitropism and strongly suggests that this cell layer functions as the gravity-sensing cell layer in dicotyledonous plant shoots. These results also demonstrate that, in addition to their previously characterized role in root radial patterning, SCR and SHR regulate the radial organization of the shoot axial organs in Arabidopsis.

Arabidopsis↗