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During mouse embryonic development cardiac tissue derives from the mesoderm to form the cardiac crescent. Within 24 hours the heart morphs from a flat crescent into a linear elongated tube that will fold on itself to carry out cardiac looping and position itself to form future cardiac chambers. Through out this entire process the heart is continuously contracting—adding more cardiomyocytes and organizing their layout to generate a contractile force that efficiently pushes blood plasma through the embryonic circulation. During this stage, the embryonic heart is composed of cardiac progenitor cells that are in the process of differentiating into mature cardiac cells. It is suspected that cardiac contraction may provide mechanical information that guides cell behavior and influences cell fate decisions. In this work, we have utilized volumetric, high-speed OCT imaging in conjunction with live mouse embryo culture to characterize how cardiac contraction patterns in the mid-gestation embryo, as the heart progresses from the cardiac crescent to the linear heart tube stage. To accomplish this, we set timed matings to obtain mouse embryos of the desired stage. Mouse embryos are live dissected and are allowed to recover in media supplemented with serum at 37°C and gassed with 5% CO2. To image these embryos, we have utilized a commercial fourier domain mode lock (FDML) OCT system to image the live embryonic mouse heart at 19 volumes/second with a 512x128 voxel element 3D OCT data set. In our approach, we customized the sample arm of the FDML system so that it may be placed within an incubator to maintain physiological conditions through the entire imagining session. At a 19Hz volume rate, single acquisitions only last several seconds and make this approach ideal for high throughput imaging. With a central wavelength of 1318nm and an axial resolution of 8.33um in air, we are able to reconstruct high resolution structural images of the mouse embryo with great temporal resolution to visualize the cardiac contraction cycle and the flow of blood cells through the lumen of the heart. We will use these datasets to characterize the patterning of contraction as the heart develops. This information will be resourceful by indicating which regions of the heart are adopting a cardiomyocyte identity and will help inform future hypothesis that attempt to determine how cardiac progenitor cells make cell fate decisions.
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