K Yamana

Kyushu University, Fukuoka-shi, Fukuoka-ken, Japan

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Publications (76)134.25 Total impact

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    ABSTRACT: Isolated cells from Xenopus laevis embryos at various developmental stages were incubated with (methyl-3H) methionine to label newly synthesized RNAs. Methylation of RNAs was studied by analyzing nuclease-digests of high-molecular-weight RNAs by DEAE-Sephadex column chromatography. Labeled rRNA, mRNA and 4s RNA were distinguished by their characteristic patterns of 2′-0-methylation and base-methylation. It was concluded that rRNA synthesis starts during the mid- to late-blastula stage. This is about 4 hr, or at least 3 cell cycles earlier than the initiation of gastrulation, which was previously considered to be the stage when rRNA synthesis begins.
    Embryologia 07/2008; 23(6):579 - 587. · 2.21 Impact Factor
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    ABSTRACT: Isolated cells from animal or vegetal pole regions of Xenopus blastulae were cultured, and the timings of rRNA synthesis and cell division were determined. rRNA synthesis was measured by the incorporation of (3H)methionine into rRNA, and cell division was studied by the decrease in cell size and rRNA content. Nucleoli in these cells were also examined. It was found that these animal and vegetal cells continue to divide under the present conditions in the same temporal pattern as that of intraembryonic cells, and that rRNA synthesis begins soon after the cells have undergone the division which probably corresponds to the 15th division following fertilization. At this time, the rRNA content and concentration of the animal and vegetal cells are significantly different. These results seem to support the view that cell division is involved in some way in the mechanism determining the timing of rRNA synthesis in early embryonic development.
    Embryologia 07/2008; 22(5):773 - 780. · 2.21 Impact Factor
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    ABSTRACT: The localization and segregation of maternal RNA's during early cleavage of Xenopus laevis embryos were studied. Blastomeres and hemispheres of eggs and early embryos were separated manually and the amounts of ribosomal RNA and poly(A) +RNA extracted from each blastomere and hemisphere were determined by optical density measurement and by 3H-poly(U) hybridization, respectively. It was found that both kinds of the maternal RNA's were more abundant (two-thirds of the total) in the animal hemisphere (cells), while they were evenly distributed between the dorsal and ventral halves. This pattern of localization remained unchanged from the egg to the blastula stage, indicating that these maternal RNA's were segregated into blastomeres quite simply by cell division. Gel electrophoresis showed that the size distributions of poly(A) +RNA and poly(A) sequences obtained from different blastomeres of 8-cell embryos did not differ greatly. It was also found that cytoplasmic polyadenylation of maternal RNA, which occurs during early cleavage and blastulation, took place equally in all regions of the cleaving embryos, suggesting no regional difference in the localization of maternally inherited nonpolyadenylated RNA. These observations are discussed in relation to previous findings on differences along the animal-vegetal and dorsal-ventral axes of the early amphibian embryo.
    Embryologia 07/2008; 23(1):23 - 32. · 2.21 Impact Factor
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    ABSTRACT: The combination of Xenopus borealis and X. laevis provides an excellent cell marking system. The potential availability of this system for chimera formation has also been suggested. However, eggs and early embryos of these species differ in size and the fusion of blastomeres of different sizez results in some disturbance in arrangement of blastomeres of a chimera. This disturbance was avoided by use of embryos from X. laevis eggs fertilized with X. borealis sperm, instead of X. borealis embryos. The cells of these hybrids could also be distinguished from the cells of X. laevis.The fate of animal ventral cells placed in the dorsal region was followed by making a chimera by fusing a right lateral half of an 8-cell X. laevis embryo with that of an 8-cell hybrid embryo. The animal ventral cells in the “dorsal” region were found to become “dorsalized”, giving rise to a lateral half of dorsal axial structures. This observation explains a previous finding that the replacement of dorsal cells by ventral ones had no effect on embryogenesis in a composite embryo.
    Embryologia 07/2008; 28(2):177 - 183. · 2.21 Impact Factor
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    Masahiro Yuge, Kiyotaka Yamana
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    ABSTRACT: To study the regulation of the dorsal axial structures, we removed the right animal dorsal and the right vegetal dorsal cells from an 8-cell embryo of Xenopus laevis.Most of the right dorsal cell-deficient embryos developed to normally proportioned tailbud embryos. No detectable delay was observed in their development. Examinations of serial sections revealed that they had restored bilateral symmetry. The cell numbers of the somite and the notochord had recovered to more than 90% and 70%, respectively, those of controls. Since the right dorsal cell-deficient embryo retained roughly three-quarters of the prospective region for the somites and half of that for the notochord, respectively, the cell number was more than that expected from the remaining prospective regions. Cell lineage analyses showed that progeny of the right ventral cells had formed almost all of the right dorsal axial structures, which are normally formed by the progeny of the right dorsal cells. However, almost all the notochord cells had been derived from the remaining left dorsal cells.These results indicate that some quantitative aspects of regulation as expressed in terms of the cell number were different between the two tissues examined.
    Embryologia 07/2008; 31(4):315 - 324. · 2.21 Impact Factor
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    ABSTRACT: We isolated a mouse monoclonal antibody (FAD-II) that disrupts cell-substratum adhesion of amphibian (Xenopus laevis) epithelial cells and endothelial cells. The effect of the antibody was cell-type specific, and the antibody had no effect on fibroblastic cells while fibronectin peptide blocked cell-substratum adhesion of all the cell types examined. In developing frog embryos, the epitopes recognized by the antibody were detected in pronephrotic ducts and in other tissue cells of embryos (from stage 33/34 afterwards). In adult tissues, the antibody mainly recognized antigens in extracelluar matrices. The antigens recognized by the antibody seems to be novel glycoepitopes in frog cells.
    Embryologia 07/2008; 33(6):639 - 649. · 2.21 Impact Factor
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    ABSTRACT: The rates of syntheses of 18S and 28S rRNA, 5S RNA, capped mRNA and 4S RNA were determined in isolated cells from pre- and post-gastrular embryos of Xenopus laevis. The rate of rRNA synthesis per nucleolated cell Mas about 0.2 pg/hr, or about 5.5 × 104 molecules/hr at the blastula stage, and this value remained constant in later stages. At the blastula stage, about 30 molecules of 5s RNA, 10 molecules of capped mRNA and 900 molecules of 4S RNA were synthesized per molecule of 18S or 28S rRNA. These values were all greatly reduced during the gastrula stage, and at the neurula stage, one molecule each of 5S RNA and capped mRNA and 10 molecules of 4S RNA were synthesized per molecule of 18S or 28S rRNA.
    Embryologia 07/2008; 23(6):589 - 597. · 2.21 Impact Factor
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    ABSTRACT: The reaggregation kinetics of frog (Xenopus laevis) cells prepared using several different dissociation procedures were monitored. Two distinct modes of cell adhesion were revealed, one mediated by Ca2+ dependent cell-cell adhesion system (CDS) and the other mediated by Ca2+ independent one (CIDS).CDS was detected in frog embryonic (two-cell stage to neurula) cells and in cells of epithelial cell lines (A6 and A8), while CIDS was detected only in A6 cells. Frog CDS was resistant to 0.01% tryptic digestion in the presence of 1 mM Ca2+ and CIDS was resistant to dilute (0.0001%) tryptic digestion. Cells with both mechanisms were prepared by dissociation with 1 mM EDTA and both mechanisms were absent in cells dissociated with 0.01% trypsin and 1 mM EDTA. Frog CDS and CIDS functioned in a temperature dependent and independent manner, respectively. Properties of frog CDS and CIDS revealed in this study were the same as those of mammalian or avian CDS and CIDS, respectively. Frog cells with CDS cross-adhered to mammalian epithelial (F9) cells but not to fibroblastic (V79) cells Ca2+ dependently. Monoclonal antibody ECCD-1 raised against mouse epithelial CDS blocked aggregation of frog A8 cells.These results suggest the similarity between frog CDS and mammalian epithelial type CDS.
    Embryologia 07/2008; 28(3):311 - 319. · 2.21 Impact Factor
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    ABSTRACT: Isolated cells of Xenopus laevis neurulae were labeled with 3H-uridine at three different temperatures (21°C, 30°C and 10°C), and the pattern of RNA synthesis was examined, using polyacrylamide gels. At 21°C (standard temperature), the synthesis of 28S and 18S ribosomal RNA (rRNA), as well as other RNAs, occurred quite actively. At 30°C (higher temperature), the syntheses of rRNA, 4S and heterogeneous RNA were all increased about twofold (Q10= 2). When the temperature was lowered to 10°C, however, the accumulation of both 28S and 18S rRNA was inhibited nearly completely, while the other RNAs were still synthesized at a 50% level. The absence of 40S rRNA precursor at 10°C makes it highly likely that at the lowered temperature the transcription of rRNA precursor is inhibited. These effects of temperature changes on RNA synthesis were all reversible: the synthesis returned to a normal rate within 4 hr in those cells that had previously been exposed to the lower or higher temperature for 6 hr.
    Embryologia 06/2008; 20(1):35 - 40. · 2.21 Impact Factor
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    ABSTRACT: The dorsal and ventral blastomeres of 4-celled embryos of Xenopus luevis were separated. During the next 14 hr in cultnre, the cell numbers of the progeny cell aggregates of the dorsal and ventral blastomeres respectively, were the same. Synthesis of 4 S RNA started after about 4 hr of culture in both kinds of progeny cell aggregates. However, a clear-cut difference was found in the time when rRNA synthesis started in these aggregates: it began after 10 hr in cell aggregates derived from the dorsal blastomeres, and after about 14 hr in those derived from the ventral blastomeres. After this, rRNA synthesis became more and more active in both types of aggregates. This is the first demonstration of differential initiation of rRNA synthesis in aggregates derived from different blastomeres but containing the same number of cells. The results provide unequivocal evidence for developmental regulation of rRNA synthesis.
    Embryologia 06/2008; 21(6):501 - 507. · 2.21 Impact Factor
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    ABSTRACT: Embryos of Xenopus laevis at stage 6 were labeled with 14CO2 for 4 hr and then allowed to develop under nonradioactive conditions until they reached stage 9, 10, 11 or 12. RNA was extracted and electrophoresed on a polyacrylamide-agarose gel. From the pattern of newly synthesized RNAs, the incorporation into 18S and 28S ribosomal RNAs was measured. At the same time, the specific radioactivity of nucleoside triphosphates in the acid-soluble fraction was determined. On the basis of the results obtained, the absolute amounts of the RNAs synthesized were calculated. The results show that the synthesis of the ribosomal RNAs begins, or is at least markedly activated, around stage 10. Moreover, cytological examination has shown that cells with nucleolated nuclei appeared between stages 9 and 10 and increased thereafter.Thus, from the results of these studies along two different lines, it can safely be concluded that the initiation of 18S and 28S RNA synthesis takes place around stage 10.
    Embryologia 06/2008; 18(4):329 - 338. · 2.21 Impact Factor
  • The Journal of cardiovascular surgery 01/1999; 39(6):873-4. · 1.51 Impact Factor
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    ABSTRACT: Patients with vascular disease and coronary disease are usually treated initially by coronary artery bypass grafting (CABG), and vascular surgery is generally performed later. In this study we assessed the feasibility of combined CABG and vascular surgery in a single operation. Between 1988 and 1995, 16 patients received combined operations for vascular and cardiac lesions and the clinical results were assessed. There were no operative or hospital deaths. The mean time for operation was 421 min and the duration of the stay in the intensive care unit (ICU) was a mean of 3.6 days. In one patient with an ischemic left leg, the left internal thoracic artery (ITA) had become a collateral source of the ischemic leg, and the need for preoperative angiography of the ITA in such patients was indicated. The combined operation clearly takes longer than either vascular surgery or CABG alone, but the length of the postoperative intensive care unit stay was essentially the same as that after a single operation and the patient was still managed safely after the combined operation. In patient requiring both operations, the combined procedure therefore appears to be safe and to have a good clinical outcome.
    Surgery Today 02/1997; 27(5):443-6. · 0.96 Impact Factor
  • K Kosuga, K Tayama, K Yamana, S Aoyagi
    Ryōikibetsu shōkōgun shirīzu. 02/1996;
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    ABSTRACT: A 58-year-old Japanese woman who had a history of aortic valve replacement for congenital bicuspid valve, was admitted for investigation of facial edema and of pulselessness of the right leg. Physical examination disclosed the patient suffering from a superior vena cava syndrome. On auscultation, a continuous murmur was heard at the left lower sternal border. Computed tomographic scans revealed aortic dissection extending from the ascending aorta to the bifurcation. Echocardiography showed an intimal flap in the dilated ascending aorta, but not abnormal blood flow from the aorta to the right atrium was detected. Cardiac catheterization and aortography, however, allowed a correct diagnosis of aortic dissection with fistula to the right atrium and with obstruction of the right common iliac artery. The patient received emergency aortic root replacement and reconstruction of the coronary arteries and then recovered uneventfully.
    The Thoracic and Cardiovascular Surgeon 11/1995; 43(5):299-301. · 0.93 Impact Factor
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    ABSTRACT: A 57-year-old man with manifestations of Marfan syndrome was referred for detail examination of cardiac murmur to our hospital. Cardioangiography showed moderate aortic valve regurgitation (2/4), and severe mitral valve regurgitation (3/4), in addition to aneurysmal dilatation of the aortic root. Moderate tricuspid valve regurgitation (2/4) was also detected by Doppler echocardiography. Aortic root replacement with the Cabrol technique, mitral valve replacement with a St. Jude Medical valve, and repair of the tricuspid valve with the bicuspidalization technique were simultaneously performed in this patient. His postoperative recovery was uneventful. In this study, we discuss about the indications of simultaneous aortic root replacement and mitral valve replacement in a patient with Marfan syndrome.
    [Zasshi] [Journal]. Nihon Kyōbu Geka Gakkai 09/1995; 43(8):1223-7.
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    ABSTRACT: A 64-year-old woman without manifestations of Marfan syndrome was referred for the close investigation of a pulsatile abdominal mass. Computed tomographic scans and magnetic resonance images revealed aneurysmal dilatation of the entire aorta, including the ascending aorta and extending to the bifurcation of the aorta, as well as tortuousness of the thoracoabdominal and abdominal aorta. Digital subtraction angiography also showed aneurysmal dilatation of the entire aorta and trivial aortic regurgitation. However, aortic annular dilatation was not found by echocardiography or aortography. The entire aorta was replaced in two stages. First, graft replacement of the ascending aorta, except for the sinus segment, and the aortic arch was performed using an elephant trunk technique under hypothermic cardiopulmonary bypass with selective cerebral perfusion. Twelve weeks later, the remaining aorta, including the descending aorta and extending to the common iliac artery on the right side, and to the common femoral artery on the left side, was replaced with a partial cardiopulmonary bypass using femoral artery and vein cannulation. We believe that patients with mega aorta syndrome are best treated by total aortic replacement. The results in the present case indicate that the elephant trunk technique is useful for extensive aortic replacement in stages, and greatly facilitates the second stage operative procedures.
    Japanese Circulation Journal 07/1995; 59(6):354-8.
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    ABSTRACT: A full length cDNA clone (cXALD3) for Xenopus laevis aldolase mRNA, which exists abundantly in oocytes, was isolated from Xenopus laevis ovary cDNA library, and its nucleotide sequence was determined. The cDNA was 1.8 kb in length and encoded 363 amino acids. From the deduced amino acid sequence and the Northern blot analysis of the RNAs from several adult tissues, this clone was concluded to be a brain-type aldolase gene. The XALD3 mRNA level per egg or embryo was high during early oogenesis, but was markedly reduced during late oogenesis and was maintained at low level during early embryogenesis until it started to increase at the late neurula stage. The mRNA was also detected in testis. The characteristic change in the temporal pattern of expression and the distribution of XALD3 mRNA among different tissues suggest a possibility that brain type aldolase may play some important roles in gametogenesis and in neurulation.
    Biochimica et Biophysica Acta 07/1994; 1218(2):153-7. · 4.66 Impact Factor
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    ABSTRACT: We report a rare case of spontaneous rupture of the ascending aorta without any evidence of aneurysm formation or aortic dissection. A woman aged 64 was admitted to our cardiac care unit as an emergency patient with severe chest pain. Her face was pale and systolic blood pressure was 70 mmHg in spite of intravenous administration of dopamine (10 micrograms/kg/min). She had a history of hypertension for two years under good medical control. No trace of the chest trauma was noted before her admission. Physical examination revealed neck vein engorgement and distant heart sounds. Chest X-ray film showed enlargement of the cardiac silhouette. ECG showed no evidence of acute coronary syndrome. Pericardial effusion with a floating hematoma-like mass was detected by 2-dimensional echocardiogram. Pericardiocentesis revealed bloody pericardial fluid (Ht: 26%). Aortagraphy was performed resulting in a clinical diagnosis of acute aortic dissection, but there were no signs of a false lumen, aneurysm formation or extravasation of the contrast medium. Although continuous pericardial drainage was performed, she suddenly lost consciousness, collapsed and died. A longitudinal intimal laceration 5 cm long was observed in the ascending aorta. Pathological examination revealed cystic medial necrosis and irregularity of the elastic fibers in the media. No atheromatous plaque was noted in the intima. Spontaneous rupture of the aorta is a life-threatening condition that requires urgent surgery.(ABSTRACT TRUNCATED AT 250 WORDS)
    Kokyu to junkan. Respiration & circulation 08/1993; 41(7):697-700.
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    ABSTRACT: Twenty patients with aneurysm or dissection of the aortic arch underwent surgical treatment using partial brachiocephalic perfusion (PBP). The right subclavian artery (SA) and common femoral artery were separately cannulated and perfused by individual pump heads. The flow to SA was 4.5-11 (9.9 +/- 1.4) ml/min/kg. The mean distal stump pressure of the left superficial temporal arteries before beginning the CPB were 36-64 (50.6 +/- 8.3) mmHg. The rectal temperature during PBP was maintained at 20.1-25.0 degrees C. The PBP time ranged 32 to 157 min. We studied the oxygen saturation of left internal jugular vein (SjO2) and cerebral circulatory index (CCI) during the PBP. SjO2 ranged from 72.9 to 99.4% and CCI were maintained at more than twice the CCI measured before beginning the CPB. We applied this simplified method (PBP) to the 20 patients with aortic aneurysms. No neurological complication were seen in these 19 patients without one patient. These clinical studies suggest that the PBP under hypothermic CPB is a safe and reliable method of cerebral protection for replacement of the aortic arch.
    Kyobu geka. The Japanese journal of thoracic surgery 08/1993; 46(8 Suppl):634-8.

Publication Stats

478 Citations
134.25 Total Impact Points


  • 1974–2008
    • Kyushu University
      • • Faculty of Sciences
      • • Department of Biology
      Fukuoka-shi, Fukuoka-ken, Japan
  • 1989–1997
    • Kurume University
      • Department of Surgery
      Куруме, Fukuoka, Japan
  • 1990–1994
    • The University of Tokyo
      Edo, Tōkyō, Japan
  • 1986
    • Kagoshima University
      Kagosima, Kagoshima, Japan