The transcription factor Foxc1a in zebrafish directly regulates expression of , encoding a transcriptional regulator of cardiac progenitor cells.

Cardiogenesis is a tightly controlled biological process required for formation of a functional heart. The transcription factor Foxc1 not only plays a crucial role in outflow tract development in mice, but is also involved in cardiac structure formation and normal function in humans. However, the molecular mechanisms by which Foxc1 controls cardiac development remain poorly understood. Previously, we reported that zebrafish embryos deficient in , an ortholog of mammalian , display pericardial edemas and die 9-10 days postfertilization. To further investigate Foxc1a's role in zebrafish cardiogenesis and identify its downstream target genes during early heart development, we comprehensively analyzed the cardiovascular phenotype of -null zebrafish embryos. Our results confirmed that -null mutants exhibit disrupted cardiac morphology, structure, and function. Performing transcriptome analysis on the mutants, we found that the expression of the cardiac progenitor marker gene was significantly decreased, but the expression of germ layer-patterning genes was unaffected. Dual-fluorescence hybridization assays revealed that and are co-expressed in the anterior lateral plate mesoderm at the somite stage. Chromatin immunoprecipitation and promoter truncation assays disclosed that Foxc1a regulates expression via direct binding to two noncanonical binding sites in the proximal promoter. Moreover, functional rescue experiments revealed that developmental stage-specific overexpression partially rescues the cardiac defects of the -null embryos. Taken together, our results indicate that during zebrafish cardiogenesis, Foxc1a is active directly upstream of .