Imaging an embryonic heartbeat: light sheet microscopy of fast zebrafish cardiac dynamics

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Poster Session 1
Anjalie Schlaeppi (5, 4), Alyssa Graves (5), Michael Weber (5), Rory Power (2), Nicola Gritti (1), Michaela Mickoleit (4), Kyle Harrington5 (3, 6), Jan Huisken (5, 7)
1. EMBL Barcelona
2. EMBL Imaging Center Heidelberg
3. Max Delbrück Center for Molecular Medicine
4. Max Planck Institute of Molecular Cell Biology and Genetics
5. Morgridge Institute for Research
6. University of Idaho
7. University of Wisconsin

Light sheet microscopy, SPIM, custom microscope, cardiac imaging, live imaging, heart, zebrafish, sample embedding, workflow, 3D reconstruction

Abstract text

To understand key developmental processes, observing them in healthy, living samples is critical. With its low photo-toxicity, deep optical penetration, speed and sensitivity, light sheet fluorescent microscopy (LSFM) is becoming the tool of choice to image a wide range of biological processes, from early development and organogenesis to regeneration. Embryonic cardiac research specifically has greatly benefited from advances in live, fast LSFM. Combined with the rapid external development, tractable genetics and translucency of the zebrafish Danio rerio, LSFM can deliver insights into cardiac form and function at high spatial and temporal resolution without significant photodamage. However, LSFM of beating hearts is challenging as it requires maintaining a healthy sample in a constricted field of view and acquiring ultrafast images to resolve the heartbeat. 

Here we describe optimized tools and solutions to study the zebrafish heart in vivo. We recommend bright transgenic lines labeling cardiac elements, new gentle embedding solutions, and report progress in immobilization techniques that avoid developmental defects and do not affect heart rate. We also propose a data acquisition and analysis pipeline adapted to cardiac imaging. With this workflow, we show that when the myocardium contracts, it applies pressure on the incompressible but mobile cardiac jelly, thus propagating forces to the endocardium. We reveal how the endocardium then prevents backward flow and allows efficient pumping. This study illustrates how a custom-built light sheet microscope and dedicated analysis tools reveal previously unseen details in the fragile, rapidly moving heart. The workflow presented here focuses on zebrafish embryonic heart imaging but can also be applied to various other samples and experiments.