Reviewer #1 (Public review): Rtf1-dependent transcriptional pausing regulates cardiogenesis

This important study shows that a controlled pause in gene reading is required for early heart cells to form during development.The authors demonstrate that loss of this pause prevents the proper activation of the heart-producing program across animal and stem cell systems.The evidence is compelling, supported by careful genomic and functional analyses that clearly define the developmental block.Overall, this work will interest developmental biologists and inspire further studies on the origins of early heart defects.