Cited4a limits cardiomyocyte dedifferentiation and proliferation during zebrafish heart regeneration.

Cardiac regeneration involves the interplay of complex interactions between many different cell types, including cardiomyocytes. In regeneration, cardiomyocytes undergo dedifferentiation and proliferation to replace lost cells at the injury border. The exact mechanism regulating this process is not completely understood. Here, we report a single nucleus RNA-sequencing profile of the injured zebrafish heart revealing distinct cardiomyocyte populations. These cardiomyocyte populations have diverse functions, including stress response, myofibril assembly, proliferation and contraction. Notably, increased expression of cited4a, a p300/CBP transcriptional coactivator, was detected in the mature contracting cardiomyocytes, but absent from proliferating cardiomyocytes, suggesting it may play a role in maintaining contractile function in a subset of cardiomyocytes. We reasoned that cited4a is induced in heart injury to maintain cardiomyocyte function and therefore cited4a+ populations are restricted from entering the cell cycle. Loss-of-function cited4a mutants were generated and, following ventricular resection, increased cardiomyocyte dedifferentiation and proliferation was observed. Our findings indicate that suppressing cited4a activity in the injured heart expands the pool of cardiomyocytes available for replacing damaged and lost myocardium and could be an approach to promote heart regeneration.