Keratin 19 (Krt19) is a novel marker gene for epicardial cells.

Epicardial cells regulate heart growth by secreting numerous growth factors and undergoing lineage specification into other cardiac lineages. However, the lack of specific marker genes for epicardial cells has hindered the understanding of this cell type in heart development. Through the analysis of a cardiac single cell mRNA sequencing dataset, we identified a novel epicardial gene named (). Further analysis of the expression patterns of and , a well-known epicardial gene, revealed their preferences in major cardiac cell types. Using lineage-tracing analysis, we analyzed labeled cells at multiple time windows and found that it labels epicardial cells at both embryonic and neonatal stages. Furthermore, we studied the function of epicardial cells using a diphtheria toxin A chain (DTA)-based cell ablation system. We discovered that labeled cells are essential for fetal heart development. Finally, we investigated the function of and labeled cells in neonatal mouse development. We observed that the ; mice displayed a smaller size after tamoxifen treatment, suggesting the potential importance of labeled cells in neonatal mouse development. Additionally, we found that ; mice died at early stages, likely due to defects in the kidney and spleen. In summary, we have identified as a new epicardial cell marker gene and further explored the function of epicardial cells using the and -mediated DTA ablation system.