Make Life Visible Yoshiaki Toyama · Atsushi Miyawaki Masaya Nakamura · Masahiro Jinzaki Editors Make Life Visible Yoshiaki Toyama • Atsushi Miyawaki Masaya Nakamura • Masahiro Jinzaki Editors Make Life Visible ISBN 978-981-13-7907-9 ISBN 978-981-13-7908-6 (eBook) https://doi.org/10.1007/978-981-13-7908-6 © The Editor(s) (if applicable) and The Author(s) 2020. This book is an open access publication. Open Access This book is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence and indicate if changes were made. The images or other third party material in this book are included in the book’s Creative Commons licence, unless indicated otherwise in a credit line to the material. 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This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore Editors Yoshiaki Toyama Department of Orthopaedic Surgery Keio University, School of Medicine Shinjuku, Tokyo, Japan Masaya Nakamura Department of Orthopaedic Surgery Keio University, School of Medicine Shinjuku, Tokyo, Japan Atsushi Miyawaki RIKEN, Center for Brain Science Laboratory for Cell Function Dynamics Wako, Saitama, Japan Masahiro Jinzaki Department of Diagnostic Radiology Keio University, School of Medicine Shinjuku, Tokyo, Japan v Preface In recent years, marked advances in imaging technology have enabled the visualiza- tion of phenomena formerly believed to be completely impossible. These technolo- gies have made major contributions to the elucidation of the pathology of diseases as well as to their diagnosis and therapy. Adding further promise for future develop- ment are imaging tools in the broad sense, such as optics and optogenetics – the revolutionary use of light to control cells and organisms. From molecular imaging to clinical images, the Japanese are world leaders in basic and clinical research of visualization. We strive to foster innovative, creative, advanced research that gives full play to imaging technology in the broad sense while exploring cross-disciplinary areas in which individual research fields interact and pursuing the development of new techniques where they fuse together. The 9th Specific Research Project, “Make Life Visible,” was established by the Uehara Memorial Foundation as a 3-year research project to support such research. In this Special Project, three areas (Sessions 1–3) were targeted from basic research to clinical application. Nineteen Japanese researchers were selected, and research was begun in 2015. Session 1. Visualizing and Controlling Molecules for Life Session 2. Imaging Disease Mechanisms Session 3. Imaging-Based Diagnosis and Therapy The 12th Uehara International Symposium 2017, entitled “Make Life Visible,” was convened in Tokyo from June 12 to 14, 2017. In this international symposium, we have built on the outcomes of the 9th Special Project, with presentations focus- ing on the cutting-edge findings of visualization technologies by the Japanese Special Project members as well as ten leading researchers invited from overseas. The aim of this symposium was to be a forum for the presentation of the latest research outcomes, future prospects, and new strategies in visualization technology, from basic research to the clinical front lines (diagnosis and treatment). vi Thanks to the speakers, most of the chapters contain a video file of this sympo- sium, and we are very pleased to be able to publish the proceedings of this exiting symposium. Tokyo, Japan Yoshiaki Toyama Saitama, Japan Atsushi Miyawaki Tokyo, Japan Masaya Nakamura Tokyo, Japan Masahiro Jinzaki Preface vii Contents Part I Visualizing and Controlling Molecules for Life 1 Photoacoustic Tomography: Deep Tissue Imaging by Ultrasonically Beating Optical Diffusion . . . . . . . . . . . . . . . . . . . . . 3 Lihong V. Wang 2 Regulatory Mechanism of Neural Progenitor Cells Revealed by Optical Manipulation of Gene Expressions . . . . . . . . . . . . . . . . . . . 9 Itaru Imayoshi, Mayumi Yamada, and Yusuke Suzuki 3 Eavesdropping on Biological Processes with Multi-dimensional Molecular Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Andrey Andreev, Scott E. Fraser, and Sara Madaan 4 Apical Cytoskeletons Help Define the Barrier Functions of Epithelial Cell Sheets in Biological Systems . . . . . . . . . . . . . . . . . . . 31 Sachiko Tsukita, Tomoki Yano, and Elisa Herawati 5 Neural Circuit Dynamics of Brain States . . . . . . . . . . . . . . . . . . . . . . . 39 Karl Deisseroth 6 Optogenetic Reconstitution: Light-Induced Assembly of Protein Complexes and Simultaneous Visualization of Their Intracellular Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Tomomi Kiyomitsu 7 19F MRI Probes with Tunable Chemical Switches . . . . . . . . . . . . . . . . 65 Kazuya Kikuchi and Tatsuya Nakamura 8 Circuit-Dependent Striatal PKA and ERK Signaling Underlying Action Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Kazuo Funabiki viii 9 Making Life Visible: Fluorescent Indicators to Probe Membrane Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Parker E. Deal, Vincent Grenier, Rishikesh U. Kulkarni, Pei Liu, Alison S. Walker, and Evan W. Miller 10 Molecular Dynamics Revealed by Single-Molecule FRET Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Tomohiro Shima and Sotaro Uemura 11 Comprehensive Approaches Using Luminescence to Studies of Cellular Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Atsushi Miyawaki and Hiroko Sakurai Part II Imaging Disease Mechanisms 12 Making Chronic Pain Visible: Risks, Mechanisms, Consequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 A. Vania Apkarian 13 Visualization of the Pathological Changes After Spinal Cord Injury ( -From Bench to Bed Side- ) . . . . . . . . . . . . . . . . . . . . . . . . 133 Masaya Nakamura 14 Multimodal Label-Free Imaging to Assess Compositional and Morphological Changes in Cells During Immune Activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 Nicholas Isaac Smith 15 Investigating In Vivo Myocardial and Coronary Molecular Pathophysiology in Mice with X-Ray Radiation Imaging Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 James T. Pearson, Hirotsugu Tsuchimochi, Takashi Sonobe, and Mikiyasu Shirai 16 Visualizing the Immune Response to Infections . . . . . . . . . . . . . . . . . . 163 Ulrich H. von Andrian 17 Imaging Sleep and Wakefulness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Takeshi Kanda, Takehiro Miyazaki, and Masashi Yanagisawa 18 Abnormal Local Translation in Dendrites Impairs Cognitive Functions in Neuropsychiatric Disorders . . . . . . . . . . . . . . 179 Ryo Endo, Noriko Takashima, and Motomasa Tanaka 19 Imaging Synapse Formation and Remodeling In Vitro and In Vivo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 Shigeo Okabe Contents ix Part III Imaging-Based Diagnosis and Therapy 20 How MRI Makes the Brain Visible . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 Denis Le Bihan 21 Application of Imaging Technology to Humans . . . . . . . . . . . . . . . . . . 213 Takahiro Matsui and Masaru Ishii 22 Theranostic Near-Infrared Photoimmunotherapy . . . . . . . . . . . . . . . 219 Hisataka Kobayashi 23 Integrated Imaging on Fatigue and Chronic Fatigue . . . . . . . . . . . . . 227 Yasuyoshi Watanabe, Masaaki Tanaka, Akira Ishii, Kei Mizuno, Akihiro Sasaki, Emi Yamano, Yilong Cui, Sanae Fukuda, Yosky Kataoka, Kozi Yamaguti, Yasuhito Nakatomi, Yasuhiro Wada, and Hirohiko Kuratsune 24 Development of Novel Fluorogenic Probes for Realizing Rapid Intraoperative Multi-color Imaging of Tiny Tumors . . . . . . . . . . . . . . 235 Yasuteru Urano 25 Coronary Heart Disease Diagnosis by FFR CT : Engineering Triumphs and Value Chain Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 249 Geoffrey D. Rubin 26 Live Imaging of the Skin Immune Responses . . . . . . . . . . . . . . . . . . . 261 Zachary Chow, Gyohei Egawa, and Kenji Kabashima 27 Development of Upright CT and Its Initial Evaluation: Effect of Gravity on Human Body and Potential Clinical Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 Masahiro Jinzaki 28 The Future of Precision Health & Integrated Diagnostics . . . . . . . . . 281 Sanjiv Sam Gambhir 29 Imaging and Therapy Against Hypoxic Tumors with 64Cu-ATSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 Yasuhisa Fujibayashi, Yukie Yoshii, Takako Furukawa, Mitsuyoshi Yoshimoto, Hiroki Matsumoto, and Tsuneo Saga Contents Part I Visualizing and Controlling Molecules for Life 3 © The Author(s) 2020 Y. Toyama et al. (eds.), Make Life Visible , https://doi.org/10.1007/978-981-13-7908-6_1 Chapter 1 Photoacoustic Tomography: Deep Tissue Imaging by Ultrasonically Beating Optical Diffusion Lihong V. Wang 1 COILab.Caltech.edu Lihong V. Wang, Ph.D., Bren Professor Caltech Optical Imaging Laboratory (COIL) Andrew and Peggy Cherng Department of Medical Engineering Department of Electrical Engineering California Institute of Technology PHOTOACOUSTIC TOMOGRAPHY: Deep Tissue Imaging by Ultrasonically Beating Optical Diffusion Photoacoustic tomography has been developed for in vivo functional, metabolic, molecular, and histologic imaging by physically combining optical and ultrasonic waves. Broad applications include early-cancer detection and brain imaging. High- resolution optical imaging—such as confocal microscopy, two-photon microscopy, and optical coherence tomography—is limited to superficial imaging within the optical diffusion limit (~1 mm in the skin) of the surface of scattering tissue. By synergistically combining light and sound, photoacoustic tomography provides deep penetration at high ultrasonic resolution and high optical contrast. Electronic Supplementary Material The online version of this chapter (https://doi. org/10.1007/978-981-13-7908-6_1) contains supplementary material, which is available to autho- rized users. L. V. Wang ( * ) California Institute of Technology, Pasadena, CA, USA e-mail: LVW@Caltech.edu; http://COILab.Caltech.edu 4 In photoacoustic computed tomography, a pulsed broad laser beam illuminates the biological tissue to generate a small but rapid temperature rise, which leads to emission of ultrasonic waves due to thermoelastic expansion. The unscattered pulsed ultrasonic waves are then detected by ultrasonic transducers. High-resolution tomographic images of optical contrast are then formed through image reconstruc- tion. Endogenous optical contrast can be used to quantify the concentration of total hemoglobin, the oxygen saturation of hemoglobin, and the concentration of mela- nin. Exogenous optical contrast can be used to provide molecular imaging and reporter gene imaging as well as glucose-uptake imaging. 2 COILab.Caltech.edu Motivations for Imaging with Light • Light-matter interaction uniquely positioned at the molecular level • Fundamental role of molecules in biology and medicine • In vivo functional imaging analogous to functional MRI • In vivo metabolic imaging analogous to PET • In vivo molecular imaging of gene expressions or disease markers • In vivo label-free histologic imaging of cancer without excision Source: Wikipedia Oxy- & deoxy- hemoglobins Glucose uptake Brain activation Melanoma hallmark Photoacoustic microscopy of cell nuclei 3 COILab.Caltech.edu Confocal or two-photon microscopy Optical coherence tomography Photoacoustic tomography Challenges in Optical Penetration LV Wang, HI Wu, Biomedical Optics (Wiley, 2007); LV Wang, JJ Yao, Nature Methods 13, 627, 2016 1 mm 1 cm 10 cm 1 m Wavefront engineering with internal guide stars? 100 μm 10 μm Classical planar optical microscopy Aberration limit: 1/scattering coefficient l l e C Diffusion limit: 10/scattering coefficient n i k S Dissipation limit: 10/attenuation coefficient n a g r O Absorption limit: 10/absorption coefficient n a m u H Depth Photon propagation 2 mm L. V. Wang 5 4 COILab.Caltech.edu Photoacoustic Computed Tomography: Deep Penetration with Optical Contrast and Ultrasonic Resolution (1) ns laser pulse (within safety limit) (5) Ultrasonic detection of unscattered phonons (acoustic scattering ~ optical scattering/1000) (4) Ultrasonic emission: 1 mK → 8 mbar (800 Pa), detectable (2) Absorption of photons (3) Rapid heating (~ mK) X Wang, Y Pang, G Ku, G Stoica, LV Wang, Nature Biotech 21, 803, 2003 In photoacoustic microscopy, a pulsed laser beam is delivered into the biological tissue to generate ultrasonic waves, which are then detected with a focused ultra- sonic transducer to form a depth resolved 1D image. Raster scanning yields 3D high-resolution tomographic images. Super-depths beyond the optical diffusion limit have been reached with high spatial resolution. The following image of a mouse brain was acquired in vivo with intact skull using optical-resolution photo- acoustic microscopy. 1 Photoacoustic Tomography: Deep Tissue Imaging by Ultrasonically Beating Optical... 6 5 COILab.Caltech.edu First Functional (Also First In Vivo ) Photoacoustic Tomography in Small Animals with Intact Scalp and Skull Left-whisker stimulation Differential absorption Max Min Right-whisker stimulation X Wang, Y Pang, G Ku, G Stoica, LV Wang, Nature Biotech 21, 803, 2003 Contralateral hemodynamic response 5 mm The annual conference on photoacoustic tomography has become the largest in SPIE’s 20,000-attendee Photonics West since 2010. Wavefront engineering and compressed ultrafast photography will be touched upon. 6 COILab.Caltech.edu Growth of Photoacoustic Tomography Largest conference since 2010 in 20,000-attendee Photonics West s r e p a p f o r e b m u N Year 0 100 200 300 400 500 600 Presentations Articles L. V. Wang 7 7 COILab.Caltech.edu Omniscale In Vivo Photoacoustic (PA) Tomography with Consistent Contrast LV Wang, S Hu, Science 335, 1458, 2012; LV Wang, Nature Photon 3, 503, 2009 • Omniscale biological research from organelles to small-animal organisms • Translation of microscopic lab discoveries to macroscopic clinical practice Organelle Cell Tissue Organ Protein 10 -2 10 -1 10 0 10 1 10 2 10 3 10 -2 10 -1 10 0 10 1 10 2 Lateral resolution Axial resolution Spatial resolution ( m m) ) m m ( h t p e d g n i g a m I Depth-resolution ratio = 200 Optical-resolution PAM Acoustic-resolution PA microscopy (PAM) Submicron PAM Sub-wavelength PAM PA nanoscopy PA macroscopy Low-freq PA tomography Selected Publications: 1. Nature Biotechnology 21, 803 (2003). 2. Nature Photonics 5, 154 (2011). 3. Science 335, 1458 (2012). 4. Nature Methods 13, 67 (2016). Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence and indicate if changes were made. The images or other third party material in this chapter are included in the chapter’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the chapter’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. 1 Photoacoustic Tomography: Deep Tissue Imaging by Ultrasonically Beating Optical... 9 © The Author(s) 2020 Y. Toyama et al. (eds.), Make Life Visible , https://doi.org/10.1007/978-981-13-7908-6_2 Chapter 2 Regulatory Mechanism of Neural Progenitor Cells Revealed by Optical Manipulation of Gene Expressions Itaru Imayoshi, Mayumi Yamada, and Yusuke Suzuki The basic-helix-loop-helix (bHLH) transcription factors Hes1, Ascl1/Mash1 and Olig2 facilitate the fate determination of astrocytes, neurons and oligodendrocytes, respectively (Imayoshi and Kageyama 2014). However, these bHLH transcription factors are co-expressed in multipotent self-renewing neural progenitor cells even before cell fate choice (Imayoshi et al. 2013). This finding indicates that these fate determination factors are differentially expressed between self-renewing and dif- ferentiating neural progenitor cells with unique expression dynamics. Live imaging analysis with fluorescent and bioluminescent proteins is a powerful strategy for monitoring expression dynamics. Our imaging results indicate that bHLH transcrip- tion factors are expressed in an oscillatory manner by neural progenitor cells, and that one of them becomes dominant in fate choice. We propose that the multipotent state of neural progenitor cells correlates with the oscillatory expression of several Electronic Supplementary Material The online version of this chapter (https://doi. org/10.1007/978-981-13-7908-6_2) contains supplementary material, which is available to autho- rized users. I. Imayoshi ( * ) Graduate School of Biostudies, Kyoto University, Kyoto, Japan Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto, Japan World Premier International Research Initiative–Institute for Integrated Cell-Material Sciences, Kyoto University, Kyoto, Japan The Hakubi Center, Kyoto University, Kyoto, Japan Japan Science and Technology Agency, Precursory Research for Embryonic Science and Technology, Saitama, Japan Medical Innovation Center/SK Project, Graduate School of Medicine, Kyoto University, Kyoto, Japan e-mail: imayoshi.itaru.2n@kyoto-u.ac.jp; iimayosh@virus.kyoto-u.ac.jp 10 bHLH transcription factors, whereas the differentiated state correlates with the sus- tained expression of a single bHLH transcription factor. To address the cousal relationships between the expression dynamics (oscillatory versus sustained) and functional outcomes (cell proliferation versus fate differentia- tion), the optogenetic approach has been employed to control the expression pat- terns of bHLH transcription factors (Imayoshi et al. 2013). We applied a novel optogenetic method (photo-activatable Gal4/UAS system) to manipulate the expres- sion patterns of bHLH transcription factors using blue light illumination, showing that oscillatory expression activates the cell proliferation of neural progenitor cells, whereas sustained expression induces cell fate determination (Fig. 2.1). Fig. 2.1 Expression dynamics of bHLH factors in multipotency and cell fate determination. (This figure was modified from Figure 5 of Imayoshi and Kageyama 2014) M. Yamada Graduate School of Biostudies, Kyoto University, Kyoto, Japan Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto, Japan World Premier International Research Initiative–Institute for Integrated Cell-Material Sciences, Kyoto University, Kyoto, Japan Medical Innovation Center/SK Project, Graduate School of Medicine, Kyoto University, Kyoto, Japan Y. Suzuki Graduate School of Biostudies, Kyoto University, Kyoto, Japan Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto, Japan Medical Innovation Center/SK Project, Graduate School of Medicine, Kyoto University, Kyoto, Japan I. Imayoshi et al. 11 References Imayoshi I, Isomura A, Harima Y, Kawaguchi K, Kori H, Miyachi H, Fujiwara T, Ishidate F, Kageyama R (2013) Oscillatory control of factors determining multipotency and fate in mouse neural progenitors. Science 342:1203–1208 Imayoshi I, Kageyama R (2014) bHLH factors in self-renewal, multipotency, and fate choice of neural progenitor cells. Neuron 82:9–23 Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence and indicate if changes were made. The images or other third party material in this chapter are included in the chapter’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the chapter’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. 2 Regulatory Mechanism of Neural Progenitor Cells Revealed by Optical... 13 © The Author(s) 2020 Y. Toyama et al. (eds.), Make Life Visible , https://doi.org/10.1007/978-981-13-7908-6_3 Chapter 3 Eavesdropping on Biological Processes with Multi-dimensional Molecular Imaging Andrey Andreev, Scott E. Fraser, and Sara Madaan 3.1 Intravital Imaging A more complete understanding of biological processes at cellular and molecular levels requires the ability to study them in time and space. Such observation became increasingly easy with the use of genetically encoded fluorescent markers, such as GFP, and the latest developments in optical microscopy. This combination of tools permits the structure and function of biological tissues to be imaged in zebrafish non-invasively. For example, it has become possible to image cardiac structure when GFP is fused to cytoskeletal elements, such as alpha-catenin; similarly, neural activity can be followed when genetically encoded calcium sensors are used to eavesdrop on sets of neurons. Such intravital imaging has furthered our understand- ing of the relationships between cardiac structure and function, as well as between neuronal activity patterns and complex behaviors such as sleep. Imaging these pro- cesses in 3 dimensions – at whole tissue scale and at subcellular resolution – is challenging to perform at sufficient speeds to capture the dynamics under study. Here we review some emerging approaches that combine the speed of Light Sheet microscopy with sets of computational image processing and image analysis tools, offering clear paths to overcome these challenges. We will take advantage of the zebrafish as an excellent system for imaging, and offer examples drawn from recent A. Andreev · S. Madaan Translational Imaging Center, Department of Molecular and Computational Biology, University of Southern California, Los Angeles, CA, USA S. E. Fraser ( * ) Translational Imaging Center, Department of Molecular and Computational Biology, University of Southern California, Los Angeles, CA, USA Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, USA e-mail: sfraser@provost.usc.edu 14 efforts to perform 3D imaging at single-cell resolution of the beating heart, and of whole-brain neural activity. 3.2 Volumetric Cardiac Imaging in Embryonic Zebrafish 3.2.1 Zebrafish As a Model System for Cardiovascular Research Congenital heart diseases (CHDs), not only represent the most prevalent birth defects in humans but also one of the leading causes of infant mortality and morbid- ity (Pierpont et al. 2007). Although several vertebrate model systems allow mecha- nistic investigations of cardiac development and of cardiac diseases, zebrafish ( Danio rerio ) offers a powerful model organism for cardiovascular development studies using imaging tools. Because of its small size, passive diffusion of oxygen can support the normal development of zebrafish embryos that are completely lack- ing a functional cardiovascular system or blood circulation; this permits analyses of embryos with severe cardiovascular defects that would be impossible in other sys- tems (Stainier et al. 1996). Because zebrafish embryos develop externally and are optically transparent, they are ideal for live, in vivo imaging of cellular and physi- ologic processes involved in cardiac morphogenesis (Hove et al. 2003). The zebraf- ish heart is small enough in size (~250 μ m × 200 μ m × 150 μ m) to be imaged in its entirety at sub-cellular resolution. Zebrafish and mammalian hearts exhibit several well conserved structures including atria, ventricles, cardiac valves and a cardiac conduction system which coordinates the contractions of the atrial and ventricular chambers and maintains a normal heart rate (Beis et al. 2005; Chi et al. 2008; Sedmera et al. 2003; Stainier et al. 1993) These conserved features make zebrafish studies of cardiac develop- ment (e.g. valve development) and physiology (e.g. cardiac conduction studies) rel- evant to human cardiac development and pathologies. The rapid development and large offspring numbers make zebrafish ideal for forward genetic screens, which have identified numerous cardiovascular mutant phenotypes. These mutants provide excellent model systems to understand human cardiac disease mechanisms, and the similarities of the mutant phenotypes to key features of some human cardiomyopathies, have resulted in the identification of novel candidate genes responsible for human cardiomyopathies. Zebrafish cardiac mutants have identified regulatory mechanisms that play crucial roles during car- diogenic specification and differentiation, migration of cardiac progenitor cells, heart tube morphogenesis, and cardiac function. For instance, the zebrafish weak atrium ( wea ) mutant has shed light on the importance of blood flow through the developing ventricle for the establishment of proper ventricle morphology (Auman et al. 2007). A. Andreev et al.