Conserved roles of GATA4 and its target gene <i>TBX2</i> in regulation of human cardiogenesis

The transcription factor GATA4 is a key mediator of cardiogenesis, regulating this process through the expression of downstream target genes, only a subset of which have been identified. Using a gain-of-function model based on pluripotent ectoderm explants from Xenopus embryos expressing GATA4, we identified a set of GATA4 targets that are also regulated by cardiogenic Nodal signalling. GATA4 was shown to be required for the expression of the target genes tbx2 and prdm1, both of which were subsequently found to have roles of their own in vivo, as downregulation of tbx2, a positive target, and overexpression of prdm1, a negative target, interferes with cardiac development in Xenopus embryos. The conservation of the GATA4-TBX2-PRDM1 regulatory relationship was demonstrated in human induced pluripotent stem cell-derived cardiomyocytes. Loss of GATA4 function resulted in downregulation of TBX2, upregulation of PRDM1 and failure of cardiogenesis. GATA4-deficient cells failed to form normal cardiomyocytes, with most cells adopting alternative fates and only a small minority displaying an aberrant cardiomyocyte phenotype. Genome-wide transcriptomic analysis documented a marked reduction in cardiomyocyte and endothelial cell transcriptomes, accompanied by upregulation of transcriptional profiles associated with smooth muscle cells and fibroblasts. Disruption of TBX2 led to the formation of cardiomyocytes with hypertrophic-like features consistent with maladaptive remodelling. In addition, although PRDM1 was not essential for cardiomyocyte formation, it appeared to play a role in fine-tuning the timing and levels of gene expression. Together, these findings establish a conserved regulatory relationship between GATA4 and its target genes TBX2 and PRDM1 and suggest important roles for these factors in modulating cardiomyocyte development.