Sall1/4 cooperatively interact with Srf/Myocd to promote cardiac cell proliferation through the regulation of Cdk/Cyclin genes

The zinc finger transcription factors, Sall1 and Sall4 are expressed in the progenitors of the second heart field (SHF) and in cardiomyocytes during the early stages of mouse development. To understand the function of Sall1/4 in heart development, we generated heart-specific Sall1/4-functional inhibition mice by forced expression of the truncated form of Sall4 (delta-Sall4) in the heart. The delta-Sall4-overexpression (OE) mice exhibited a hypoplastic right ventricle and outflow tract, both of which were derived from SHF, and a thinner ventricular wall. We found that the numbers of proliferative SHF progenitors and cardiomyocytes were dramatically reduced in delta-Sall4-OE mice. RNA-sequencing data showed that Sall1/4 act upstream of the Cdk/Cyclin genes and cardiomyocyte compaction-related genes, including Myocd. In addition, ChIP-sequencing and co-immunoprecipitation analyses revealed that Sall4 and Myocd form a transcriptional complex with Srf and directly bind to the upstream regulatory regions of the Cdk/Cyclin genes (Cdk1, Ccne2, and Ccnb1). These results suggest that Sall1/4 are critical for the proliferation of cardiac cells via regulation of Cdk/cyclin genes interacting with Srf/Myocd.