The role of biomechanical signaling is well accepted as a modulator of cardiac cell behavior and a requirement for cardiac morphogenesis. However, the small, fragile nature of the embryonic heart makes it difficult to determine transient mechanical homeostasis during heart development and search for causal links between biomechanical forces and cardiac cell behavior in vivo. Toward this problem, we have developed a set of methods for live dynamic optical coherence tomography (OCT) imaging of the developing heart in cultured mouse embryos, starting at earliest stages. To manipulate cardiodynamics in live embryo culture, we have successfully established cardiac optogenetics to control heartbeat frequency in the embryonic mouse heart for the first time. By coupling OCT imaging with optogenetic control, we can generate 4D (3D+time) images of the heart and extract structural and functional information such as heart wall dynamics and blood flow velocity during optogenetic manipulation. As a way to quantify organization of structural fibers in early embryonic hearts, we implemented second harmonic generation, an unbiased imaging approach to detect collagen. Using optogenetic cardiac pacing and second harmonic generation imaging, we will look at how changes in heart biomechanics are consequential in the deposition and organization of cardiac collagen. This work is bringing us closer to understanding how mechanical stimuli from heart contraction regulate mechanical homeostasis and cardiac differentiation in vivo, potentially contributing to management of congenital heart defects.
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