Details of a Researcher - Hashimoto, Hisayuki

Papers - Hashimoto, Hisayuki

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H1foo Has a Pivotal Role in Qualifying Induced Pluripotent Stem Cells.

Kunitomi A, Yuasa S, Sugiyama F, Saito Y, Seki T, Kusumoto D, Kashimura S, Takei M, Tohyama S, Hashimoto H, Egashira T, Tanimoto Y, Mizuno S, Tanaka S, Okuno H, Yamazawa K, Watanabe H, Oda M, Kaneda R, Matsuzaki Y, Nagai T, Okano H, Yagami KI, Tanaka M, Fukuda K

Stem cell reports (CELL PRESS) 6 ( 6 ) 825 - 833 2016.06

Research paper (scientific journal), Joint Work, Accepted, ISSN 22136711

Embryonic stem cells (ESCs) are a hallmark of ideal pluripotent stem cells. Epigenetic reprogramming of induced pluripotent stem cells (iPSCs) has not been fully accomplished. iPSC generation is similar to somatic cell nuclear transfer (SCNT) in oocytes, and this procedure can be used to generate ESCs (SCNT-ESCs), which suggests the contribution of oocyte-specific constituents. Here, we show that the mammalian oocyte-specific linker histone H1foo has beneficial effects on iPSC generation. Induction of H1foo with Oct4, Sox2, and Klf4 significantly enhanced the efficiency of iPSC generation. H1foo promoted in vitro differentiation characteristics with low heterogeneity in iPSCs. H1foo enhanced the generation of germline-competent chimeric mice from iPSCs in a manner similar to that for ESCs. These findings indicate that H1foo contributes to the generation of higher-quality iPSCs.

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Analysis of cardiomyocyte movement in the developing murine heart.

Hashimoto H, Yuasa S, Tabata H, Tohyama S, Seki T, Egashira T, Hayashiji N, Hattori F, Kusumoto D, Kunitomi A, Takei M, Kashimura S, Yozu G, Shimojima M, Motoda C, Muraoka N, Nakajima K, Sakaue-Sawano A, Miyawaki A, Fukuda K

Biochemical and biophysical research communications (ACADEMIC PRESS INC ELSEVIER SCIENCE) 464 ( 4 ) 1000 - 1007 2015.09

Research paper (scientific journal), Joint Work, Accepted, ISSN 0006-291X

The precise assemblage of several types of cardiac precursors controls heart organogenesis. The cardiac precursors show dynamic movement during early development and then form the complicated heart structure. However, cardiomyocyte movements inside the newly organized mammalian heart remain unclear. We previously established the method of ex vivo time-lapse imaging of the murine heart to study cardiomyocyte behavior by using the Fucci (fluorescent ubiquitination-based cell cycle indicator) system, which can effectively label individual G1, S/G2/M, and G1/S-transition phase nuclei in living cardiomyocytes as red, green, and yellow, respectively. Global analysis of gene expression in Fucci green positive ventricular cardiomyocytes confirmed that cell cycle regulatory genes expressed in G1/S, S, G2/M, and M phase transitions were upregulated. Interestingly, pathway analysis revealed that many genes related to the cell cycle were significantly upregulated in the Fucci green positive ventricular cardiomyocytes, while only a small number of genes related to cell motility were upregulated. Time-lapse imaging showed that murine proliferating cardiomyocytes did not exhibit dynamic movement inside the heart, but stayed on site after entering the cell cycle.

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Erratum: G-CSF supports long-term muscle regeneration in mouse models of muscular dystrophy.

Hayashiji N, Yuasa S, Miyagoe-Suzuki Y, Hara M, Ito N, Hashimoto H, Kusumoto D, Seki T, Tohyama S, Kodaira M, Kunitomi A, Kashimura S, Takei M, Saito Y, Okata S, Egashira T, Endo J, Sasaoka T, Takeda S, Fukuda K

Nature communications (NATURE PUBLISHING GROUP) 6 7295 - 7295 2015.06

Joint Work, Accepted, ISSN 2041-1723

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Patients with reduced heart rate response to adenosine infusion have low myocardial flow reserve in N-13-ammonia PET studies

Takeshi Tomiyama, Shin-ichiro Kumita, Keiichi Ishihara, Masaya Suda, Minoru Sakurai, Kenta Hakozaki, Hidenobu Hashimoto, Naoto Takahashi, Hitoshi Takano, Yasuhiro Kobayashi, Tomonari Kiriyama, Yoshimitsu Fukushima, Wataru Shimizu

INTERNATIONAL JOURNAL OF CARDIOVASCULAR IMAGING (SPRINGER) 31 ( 5 ) 1089 - 1095 2015.06

Research paper (scientific journal), Joint Work, Accepted, ISSN 1569-5794

To assess the effect of adenosine infusion by evaluating the relationship between heart rate (HR) response to adenosine and myocardial flow reserve (MFR) of remote regions supplied by normal coronary arteries in N-13-ammonia PET. Thirty-one consecutive subjects (20 known coronary artery disease patients, 4 chronic heart failure patients, and 7 normal volunteers) except cases having 3-vessel disease underwent rest and adenosine stress N-13-ammonia myocardial perfusion PET. Semi-quantitative, quantitative, and gated analyses were performed. Subjects were divided into two groups with regard to HR response to adenosine. Twenty-two subjects had normal HR response (peak/rest HR > 1.20), while reduced HR response (a parts per thousand currency sign1.20) was observed in nine subjects. There were no differences in rest myocardial blood flow (MBF) of remote regions between the groups. Subjects with reduced HR response had significantly lower stress MBF and MFR of remote regions than those with normal HR response (stress MBF: 1.559 +/- A 0.517 vs. 2.279 +/- A 0.530, p = 0.004, MFR: 1.59 +/- A 0.36 vs. 2.35 +/- A 0.53, p = 0.001). There were no significant differences between the groups by means of semi-quantitative scoring. Rest and stress ejection fraction (EF) in the reduced HR response group was lower than that in the normal HR response group. In a multiple stepwise regression analysis, HR ratio, dyslipidemia, and Brinkman index were identified as predictors of the change in MFR of remote regions. Subjects with reduced HR response to adenosine had lower stress MBF and MFR of remote regions and lower EF. Moreover, HR response was one of the predictors of the change in MFR of remote regions.

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G-CSF supports long-term muscle regeneration in mouse models of muscular dystrophy.

Nature communications (NATURE PUBLISHING GROUP) 6 6745 - 6745 2015.04

Research paper (scientific journal), Joint Work, Accepted, ISSN 2041-1723

Duchenne muscular dystrophy (DMD) is a chronic and life-threatening disease that is initially supported by muscle regeneration but eventually shows satellite cell exhaustion and muscular dysfunction. The life-long maintenance of skeletal muscle homoeostasis requires the satellite stem cell pool to be preserved. Asymmetric cell division plays a pivotal role in the maintenance of the satellite cell pool. Here we show that granulocyte colony-stimulating factor receptor (G-CSFR) is asymmetrically expressed in activated satellite cells. G-CSF positively affects the satellite cell population during multiple stages of differentiation in ex vivo cultured fibres. G-CSF could be important in developing an effective therapy for DMD based on its potential to modulate the supply of multiple stages of regenerated myocytes. This study shows that the G-CSF-G-CSFR axis is fundamentally important for long-term muscle regeneration, functional maintenance and lifespan extension in mouse models of DMD with varying severities.

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Impaired respiratory function in MELAS-induced pluripotent stem cells with high heteroplasmy levels.

Kodaira M, Hatakeyama H, Yuasa S, Seki T, Egashira T, Tohyama S, Kuroda Y, Tanaka A, Okata S, Hashimoto H, Kusumoto D, Kunitomi A, Takei M, Kashimura S, Suzuki T, Yozu G, Shimojima M, Motoda C, Hayashiji N, Saito Y, Goto Y, Fukuda K

FEBS open bio (ELSEVIER SCIENCE LONDON) 5 219 - 225 2015

Research paper (scientific journal), Joint Work, Accepted, ISSN 22115463

Mitochondrial diseases are heterogeneous disorders, caused by mitochondrial dysfunction. Mitochondria are not regulated solely by nuclear genomic DNA but by mitochondrial DNA. It is difficult to develop effective therapies for mitochondrial disease because of the lack of mitochondrial disease models. Mitochondrial myopathy, encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is one of the major mitochondrial diseases. The aim of this study was to generate MELAS-specific induced pluripotent stem cells (iPSCs) and to demonstrate that MELAS-iPSCs can be models for mitochondrial disease. We successfully established iPSCs from the primary MELAS-fibroblasts carrying 77.7% of m.3243A>G heteroplasmy. MELAS-iPSC lines ranged from 3.6% to 99.4% of m.3243A>G heteroplasmy levels. The enzymatic activities of mitochondrial respiratory complexes indicated that MELAS-iPSC-derived fibroblasts with high heteroplasmy levels showed a deficiency of complex I activity but MELAS-iPSC-derived fibroblasts with low heteroplasmy levels showed normal complex I activity. Our data indicate that MELAS-iPSCs can be models for MELAS but we should carefully select MELAS-iPSCs with appropriate heteroplasmy levels and respiratory functions for mitochondrial disease modeling.

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MiR-133 promotes cardiac reprogramming by directly repressing Snai1 and silencing fibroblast signatures.

Muraoka N, Yamakawa H, Miyamoto K, Sadahiro T, Umei T, Isomi M, Nakashima H, Akiyama M, Wada R, Inagawa K, Nishiyama T, Kaneda R, Fukuda T, Takeda S, Tohyama S, Hashimoto H, Kawamura Y, Goshima N, Aeba R, Yamagishi H, Fukuda K, Ieda M

The EMBO journal (WILEY-BLACKWELL) 33 ( 14 ) 1565 - 1581 2014.07

Research paper (scientific journal), Joint Work, Accepted, ISSN 0261-4189

Fibroblasts can be directly reprogrammed into cardiomyocyte-like cells (iCMs) by overexpression of cardiac transcription factors or microRNAs. However, induction of functional cardiomyocytes is inefficient, and molecular mechanisms of direct reprogramming remain undefined. Here, we demonstrate that addition of miR-133a (miR-133) to Gata4, Mef2c, and Tbx5 (GMT) or GMT plus Mesp1 and Myocd improved cardiac reprogramming from mouse or human fibroblasts by directly repressing Snai1, a master regulator of epithelial-to-mesenchymal transition. MiR-133 overexpression with GMT generated sevenfold more beating iCMs from mouse embryonic fibroblasts and shortened the duration to induce beating cells from 30 to 10 days, compared to GMT alone. Snai1 knockdown suppressed fibroblast genes, upregulated cardiac gene expression, and induced more contracting iCMs with GMT transduction, recapitulating the effects of miR-133 overexpression. In contrast, overexpression of Snai1 in GMT/miR-133-transduced cells maintained fibroblast signatures and inhibited generation of beating iCMs. MiR-133-mediated Snai1 repression was also critical for cardiac reprogramming in adult mouse and human cardiac fibroblasts. Thus, silencing fibroblast signatures, mediated by miR-133/Snai1, is a key molecular roadblock during cardiac reprogramming.

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Time-lapse imaging of cell cycle dynamics during development in living cardiomyocyte.

Hisayuki Hashimoto, Shinsuke Yuasa, Hidenori Tabata, Shugo Tohyama, Nozomi Hayashiji, Fumiyuki Hattori, Naoto Muraoka, Toru Egashira, Shinichiro Okata, Kojiro Yae, Tomohisa Seki, Takahiko Nishiyama, Kazunori Nakajima, Asako Sakaue-Sawano, Atsushi Miyawaki, Keiichi Fukuda

Journal of molecular and cellular cardiology (ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD) 72 241 - 9 2014.07

Research paper (scientific journal), Joint Work, Accepted, ISSN 0022-2828

Mammalian cardiomyocytes withdraw from the cell cycle shortly after birth, although it remains unclear how cardiomyocyte cell cycles behave during development. Compared to conventional immunohistochemistry in static observation, time-lapse imaging can reveal comprehensive data in hard-to-understand biological phenomenon. However, there are no reports of an established protocol of successful time-lapse imaging in mammalian heart. Thus, it is valuable to establish a time-lapse imaging system to enable the observation of cell cycle dynamics in living murine cardiomyocytes. This study sought to establish time-lapse imaging of murine heart to study cardiomyocyte cell cycle behavior. The Fucci (fluorescent ubiquitination-based cell cycle indicator) system can effectively label individual G1, S/G2/M, and G1/S-transition phase nuclei red, green and yellow, respectively, in living mammalian cells, and could therefore be useful to visualize the real-time cell cycle transitions in living murine heart. To establish a similar system for time-lapse imaging of murine heart, we first developed an ex vivo culture system, with the culture conditions determined in terms of sample state, serum concentration, and oxygen concentration. The optimal condition (slice culture, oxygen concentration 20%, serum concentration 10%) successfully mimicked physiological cardiomyocyte proliferation in vivo. Time-lapse imaging of cardiac slices from E11.5, E14.5, E18.5, and P1 Fucci-expressing transgenic mice revealed an elongated S/G2/M phase in cardiomyocytes during development. Our time-lapse imaging of murine heart revealed a gradual elongation of the S/G2/M phase during development in living cardiomyocytes.

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Generation and characterization of functional cardiomyocytes derived from human T cell-derived induced pluripotent stem cells.

Seki T, Yuasa S, Kusumoto D, Kunitomi A, Saito Y, Tohyama S, Yae K, Kishino Y, Okada M, Hashimoto H, Takei M, Egashira T, Kodaira M, Kuroda Y, Tanaka A, Okata S, Suzuki T, Murata M, Fujita J, Fukuda K

PloS one (PUBLIC LIBRARY SCIENCE) 9 ( 1 ) e85645 2014

Research paper (scientific journal), Joint Work, Accepted, ISSN 1932-6203

Induced pluripotent stem cells (iPSCs) have been proposed as novel cell sources for genetic disease models and revolutionary clinical therapies. Accordingly, human iPSC-derived cardiomyocytes are potential cell sources for cardiomyocyte transplantation therapy. We previously developed a novel generation method for human peripheral T cell-derived iPSCs (TiPSCs) that uses a minimally invasive approach to obtain patient cells. However, it remained unknown whether TiPSCs with genomic rearrangements in the T cell receptor (TCR) gene could differentiate into functional cardiomyocyte in vitro. To address this issue, we investigated the morphology, gene expression pattern, and electrophysiological properties of TiPSC-derived cardiomyocytes differentiated by floating culture. RT-PCR analysis and immunohistochemistry showed that the TiPSC-derived cardiomyocytes properly express cardiomyocyte markers and ion channels, and show the typical cardiomyocyte morphology. Multiple electrode arrays with application of ion channel inhibitors also revealed normal electrophysiological responses in the TiPSC-derived cardiomyocytes in terms of beating rate and the field potential waveform. In this report, we showed that TiPSCs successfully differentiated into cardiomyocytes with morphology, gene expression patterns, and electrophysiological features typical of native cardiomyocytes. TiPSCs-derived cardiomyocytes obtained from patients by a minimally invasive technique could therefore become disease models for understanding the mechanisms of cardiac disease and cell sources for revolutionary cardiomyocyte therapies.

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Testosterone induces cardiomyocyte differentiation from embryonic stem cells.

Hashimoto H, Yuasa S

Journal of molecular and cellular cardiology (ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD) 62 69 - 71 2013.09

Joint Work, Accepted, ISSN 0022-2828

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Distinct metabolic flow enables large-scale purification of mouse and human pluripotent stem cell-derived cardiomyocytes.

Tohyama S, Hattori F, Sano M, Hishiki T, Nagahata Y, Matsuura T, Hashimoto H, Suzuki T, Yamashita H, Satoh Y, Egashira T, Seki T, Muraoka N, Yamakawa H, Ohgino Y, Tanaka T, Yoichi M, Yuasa S, Murata M, Suematsu M, Fukuda K

Cell stem cell (Cell Stem Cell) 12 ( 1 ) 127 - 137 2013.01

Research paper (scientific journal), Joint Work, Accepted, ISSN 1934-5909

Heart disease remains a major cause of death despite advances in medical technology. Heart-regenerative therapy that uses pluripotent stem cells (PSCs) is a potentially promising strategy for patients with heart disease, but the inability to generate highly purified cardiomyocytes in sufficient quantities has been a barrier to realizing this potential. Here, we report a nongenetic method for mass-producing cardiomyocytes from mouse and human PSC derivatives that is based on the marked biochemical differences in glucose and lactate metabolism between cardiomyocytes and noncardiomyocytes, including undifferentiated cells. We cultured PSC derivatives with glucose-depleted culture medium containing abundant lactate and found that only cardiomyocytes survived. Using this approach, we obtained cardiomyocytes of up to 99% purity that did not form tumors after transplantation. We believe that our technological method broadens the range of potential applications for purified PSC-derived cardiomyocytes and could facilitate progress toward PSC-based cardiac regenerative therapy.

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Distinct iPS Cells Show Different Cardiac Differentiation Efficiency.

Ohno Y, Yuasa S, Egashira T, Seki T, Hashimoto H, Tohyama S, Saito Y, Kunitomi A, Shimoji K, Onizuka T, Kageyama T, Yae K, Tanaka T, Kaneda R, Hattori F, Murata M, Kimura K, Fukuda K

Stem cells international (HINDAWI PUBLISHING CORPORATION) 2013 659739 - 659739 2013

Research paper (scientific journal), Joint Work, Accepted, ISSN 1687-966X

Patient-specific induced pluripotent stem (iPS) cells can be generated by introducing transcription factors that are highly expressed in embryonic stem (ES) cells into somatic cells. This opens up new possibilities for cell transplantation-based regenerative medicine by overcoming the ethical issues and immunological problems associated with ES cells. Despite the development of various methods for the generation of iPS cells that have resulted in increased efficiency, safety, and general versatility, it remains unknown which types of iPS cells are suitable for clinical use. Therefore, the aims of the present study were to assess (1) the differentiation potential, time course, and efficiency of different types of iPS cell lines to differentiate into cardiomyocytes in vitro and (2) the properties of the iPS cell-derived cardiomyocytes. We found that high-quality iPS cells exhibited better cardiomyocyte differentiation in terms of the time course and efficiency of differentiation than low-quality iPS cells, which hardly ever differentiated into cardiomyocytes. Because of the different properties of the various iPS cell lines such as cardiac differentiation efficiency and potential safety hazards, newly established iPS cell lines must be characterized prior to their use in cardiac regenerative medicine.

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Disease characterization using LQTS-specific induced pluripotent stem cells.

Egashira T, Yuasa S, Suzuki T, Aizawa Y, Yamakawa H, Matsuhashi T, Ohno Y, Tohyama S, Okata S, Seki T, Kuroda Y, Yae K, Hashimoto H, Tanaka T, Hattori F, Sato T, Miyoshi S, Takatsuki S, Murata M, Kurokawa J, Furukawa T, Makita N, Aiba T, Shimizu W, Horie M, Kamiya K, Kodama I, Ogawa S, Fukuda K

Cardiovascular research (OXFORD UNIV PRESS) 95 ( 4 ) 419 - 429 2012.09

Research paper (scientific journal), Joint Work, Accepted, ISSN 0008-6363

AIMS: Long QT syndrome (LQTS) is an inheritable and life-threatening disease; however, it is often difficult to determine disease characteristics in sporadic cases with novel mutations, and more precise analysis is necessary for the successful development of evidence-based clinical therapies. This study thus sought to better characterize ion channel cardiac disorders using induced pluripotent stem cells (iPSCs). METHODS AND RESULTS: We reprogrammed somatic cells from a patient with sporadic LQTS and from controls, and differentiated them into cardiomyocytes through embryoid body (EB) formation. Electrophysiological analysis of the LQTS-iPSC-derived EBs using a multi-electrode array (MEA) system revealed a markedly prolonged field potential duration (FPD). The IKr blocker E4031 significantly prolonged FPD in control- and LQTS-iPSC-derived EBs and induced frequent severe arrhythmia only in LQTS-iPSC-derived EBs. The IKs blocker chromanol 293B did not prolong FPD in the LQTS-iPSC-derived EBs, but significantly prolonged FPD in the control EBs, suggesting the involvement of IKs disturbance in the patient. Patch-clamp analysis and immunostaining confirmed a dominant-negative role for 1893delC in IKs channels due to a trafficking deficiency in iPSC-derived cardiomyocytes and human embryonic kidney (HEK) cells. CONCLUSIONS: This study demonstrated that iPSCs could be useful to characterize LQTS disease as well as drug responses in the LQTS patient with a novel mutation. Such analyses may in turn lead to future progress in personalized medicine.

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miR-142-3p is essential for hematopoiesis and affects cardiac cell fate in zebrafish.

Nishiyama T, Kaneda R, Ono T, Tohyama S, Hashimoto H, Endo J, Tsuruta H, Yuasa S, Ieda M, Makino S, Fukuda K

Biochemical and biophysical research communications (ACADEMIC PRESS INC ELSEVIER SCIENCE) 425 ( 4 ) 755 - 761 2012.09

Research paper (scientific journal), Joint Work, Accepted, ISSN 0006-291X

MicroRNAs (miRNAs) play a pivotal role during embryonic development and are required for proper organogenesis, including hematopoiesis. Recent studies suggest that, in the early mesoderm, there is an interaction between the hematopoietic and cardiac lineages. However, whether miRNAs can affect other lineages remains unknown. Therefore, we investigated whether hematopoietic miR-142-3p modulated the mesoderm formation. We report that knockdown (KD) of miR-142-3p, a hematopoietic-specific miRNA, in zebrafish resulted in loss of hematopoiesis during embryonic development. Intriguingly, we observed abnormal cardiac phenotypes and insufficiency of somitegenesis in KD-morphants. In the early developmental stage, a tiny heart, contractile dysfunction in the ventricle, cardiac arrhythmia (e.g. a 2:1 ratio of atrial:ventricular beating), and bradycardia were consistently observed. Histological examination revealed severe hypoplasia of the ventricle and disrupted muscle alignment. To determine the mechanism, we performed DNA microarray analysis. The results revealed that the expression of several mesodermal genes essential for the formation of cardiac and somatic mesoderm, such as no tail, T-box gene 16, mesoderm posterior a, one eye pinhead, and rho-associated, coiled-coil containing protein kinase (Rock2a), were increased in miR-142-3p KD-morphants. The luciferase reporter assay revealed that miR-142-3p repressed luciferase activity on the Rock2a 3'-UTR. The findings of the present study indicate that miR-142-3p plays a critical role in hematopoiesis, cardiogenesis, and somitegenesis in the early stage of mesoderm formation via regulation of Rock2a.

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RESIDUAL TRANSGENE EXPRESSION OF YAMANAKA FACTORS DETERMINE QUALITY AND DIFFERENTIATION EFFICIENCY OF CARDIOMYOCYTES DERIVED FROM MOUSE INDUCED PLURIPOTENT STEM CELL LINES

Yohei Ohno, Shinsuke Yuasa, Toru Egashira, Tomohisa Seki, Hisayuki Hashimoto, Shugo Tohyama, Masaki Kodaira, Dai Kusumoto, Fumiyuki Hattori, Kojiro Yae, Mitsushige Murata, Keiichi Fukuda

JOURNAL OF THE AMERICAN COLLEGE OF CARDIOLOGY (ELSEVIER SCIENCE INC) 59 ( 13 ) E1001 - E1001 2012.03

Joint Work, Accepted, ISSN 0735-1097

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Generation of induced pluripotent stem cells from human terminally differentiated circulating T cells.

Seki T, Yuasa S, Oda M, Egashira T, Yae K, Kusumoto D, Nakata H, Tohyama S, Hashimoto H, Kodaira M, Okada Y, Seimiya H, Fusaki N, Hasegawa M, Fukuda K

Cell stem cell (CELL PRESS) 7 ( 1 ) 11 - 14 2010.07

Research paper (scientific journal), Joint Work, Accepted, ISSN 1934-5909

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Zac1 is an essential transcription factor for cardiac morphogenesis.

Yuasa S, Onizuka T, Shimoji K, Ohno Y, Kageyama T, Yoon SH, Egashira T, Seki T, Hashimoto H, Nishiyama T, Kaneda R, Murata M, Hattori F, Makino S, Sano M, Ogawa S, Prall OW, Harvey RP, Fukuda K

Circulation research (LIPPINCOTT WILLIAMS & WILKINS) 106 ( 6 ) 1083 - 1091 2010.04

Research paper (scientific journal), Joint Work, Accepted, ISSN 0009-7330

RATIONALE: The transcriptional networks guiding heart development remain poorly understood, despite the identification of several essential cardiac transcription factors. OBJECTIVE: To isolate novel cardiac transcription factors, we performed gene chip analysis and found that Zac1, a zinc finger-type transcription factor, was strongly expressed in the developing heart. This study was designed to investigate the molecular and functional role of Zac1 as a cardiac transcription factor. METHODS AND RESULTS: Zac1 was strongly expressed in the heart from cardiac crescent stages and in the looping heart showed a chamber-restricted pattern. Zac1 stimulated luciferase reporter constructs driven by ANF, BNP, or alphaMHC promoters. Strong functional synergy was seen between Zac1 and Nkx2-5 on the ANF promoter, which carries adjacent Zac1 and Nkx2-5 DNA-binding sites. Zac1 directly associated with the ANF promoter in vitro and in vivo, and Zac1 and Nkx2-5 physically associated through zinc fingers 5 and 6 in Zac1, and the homeodomain in Nkx2-5. Zac1 is a maternally imprinted gene and is the first such gene found to be involved in heart development. Homozygous and paternally derived heterozygous mice carrying an interruption in the Zac1 locus showed decreased levels of chamber and myofilament genes, increased apoptotic cells, partially penetrant lethality and morphological defects including atrial and ventricular septal defects, and thin ventricular walls. CONCLUSIONS: Zac1 plays an essential role in the cardiac gene regulatory network. Our data provide a potential mechanistic link between Zac1 in cardiogenesis and congenital heart disease manifestations associated with genetic or epigenetic defects in an imprinted gene network.

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A novel GDP-dependent pyruvate kinase isozyme from Toxoplasma gondii localizes to both the apicoplast and the mitochondrion.

Saito T, Nishi M, Lim MI, Wu B, Maeda T, Hashimoto H, Takeuchi T, Roos DS, Asai T

The Journal of biological chemistry (AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC) 283 ( 20 ) 14041 - 14052 2008.05

Research paper (scientific journal), Joint Work, Accepted, ISSN 0021-9258

We previously reported a cytosolic pyruvate kinase (EC 2.7.1.40) from Toxoplasma gondii (TgPyKI) that differs from most eukaryotic pyruvate kinases in being regulated by glucose 6-phosphate rather than fructose 1,6-diphosphate. Another putative pyruvate kinase (TgPyKII) was identified from parasite genome, which exhibits 32% amino acid sequence identity to TgPyKI and retains pyruvate kinase signature motifs and amino acids essential for substrate binding and catalysis. Whereas TgPyKI is most closely related to plant/algal enzymes, phylogenetic analysis suggests a proteobacterial origin for TgPyKII. Enzymatic characterization of recombinant TgPyKII shows a high pH optimum at 8.5, and a preference for GDP as a phosphate recipient. Catalytic activity is independent of K+, and no allosteric or regulatory effects were observed in the presence of fructose 1,6-diphosphate, fructose 2,6-diphosphate, glucose 6-phosphate, ribose 5-phosphate, AMP, or ATP. Unlike TgPyKI, native TgPyKII activity was exclusively associated with the membranous fraction of a T. gondii tachyzoite lysate. TgPyKII possesses a long N-terminal extension containing five putative start codons before the conserved region and localizes to both apicoplast and mitochondrion by immunofluorescence assay using native antibody and fluorescent protein fusion to the N-terminal extension. Further deletional and site-directed mutagenesis suggests that a translation product from 1st Met is responsible for the localization to the apicoplast, whereas one from 3rd Met is for the mitochondrion. This is the first study of a potential mitochondrial pyruvate kinase in any system.

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