PROJECT SUMMARY/ABSTRACT: The adult zebrafish has an incredible ability to regenerate up to 20% of its heart after ventricular resection. In comparison, adult humans have little to no regenerative ability. In the zebrafish, this process is known to be driven by pre-existing cardiomyocytes in the heart, but the specific sub-populations of cardiomyocytes involved is not known. Cardiac neural crest cells migrate during development and contribute to several structures in the heart, including a subpopulation of these cardiomyocytes. Though these neural crest derived cardiomyocytes (NCCMs) make up less than 15% of all zebrafish cardiomyocytes, they are essential for proper heart development and function. Thus, we hypothesize that NCCMs may also be essential for proper cardiac regeneration. I aim to dissect the unique contribution of NCCMs to zebrafish cardiac regeneration by measuring their participation in and necessity for distinct stages of cardiac regeneration. I will accomplish this by quantifying NCCMs in comparison to other cardiomyocytes during regeneration utilizing a combination of inducible transgenic manipulations, single cell genomics, and in situ techniques. Interestingly, the ratio of NCCMs to MCMs is conserved in the zebrafish, chick, and mouse though their ability to regenerate differs. Thus, it is not just the presence or absence of NCCMs that confer regenerative ability, but a unique feature of zebrafish NCCMs. I aim to determine the unique gene regulatory circuits in NCCMs during regeneration and the necessary components for cardiac regeneration. This approach will uncover the role of NCCMs and developing neural crest gene regulation in zebrafish cardiac regeneration. Further, this data will help generate future hypotheses and subsequent genetic targets for the investigation of the differential ability to regenerate the heart among species. Ultimately, this work will contribute to our understanding of the role of a unique neural crest derivative in regeneration and generate potential routes of regenerative therapies for heart disease in human patients.