Transient Ddx61-enriched condensates refine heart regeneration programs

Gene regulatory mechanisms that underlie tissue regeneration have been largely studied at the level of transcription. Here, proximity labeling methods identified enhanced presence of Processing body (P-body) marker, Ddx61, in zebrafish heart muscle cells induced to divide by injury or mitogenic stimulation. We found that Ddx61-containing condensates emerge and develop complex, transient structures in cardiomyocytes during cardiogenic settings in adult zebrafish, developing mice, and human stem cell-derived myocardium. Mutations in zebrafish ddx61 disrupted cardiomyocyte cycling and differentiation after cardiac injury or mitogen presence, and DDX61 knockdown in human cardiomyocytes inhibited similar parameters under maturation conditions in vitro. RNA affinity and proteomic profiling implicated mRNAs preferentially associating with Ddx61 during regeneration, and induced transgenic expression of one of these mRNAs, encoding the BMP signaling inhibitor, Chordin, disrupted indicators of heart regeneration after cardiac injury. Our experiments provide evidence that mRNA sorting by specialized context-dependent condensates can modulate gene expression and impact tissue regenerative capacity. Ddx61/Ddx6 pulldown and isolation of associated mRNAs during heart regeneration in zebrafish. For this 120 hearts were used for one sample. Uninjured and 14 days post injury hearts were used. Dublicate samples for each condition.