Transcription regulator (PubMed:18941117, PubMed:33833125). Plays a role in erythropoiesis, binding to promoters and activating transcription of embryonic alpha globin e1 hbae1.1 and microRNA mir-144, in erythroid progenitors; perhaps acting as part of a negative feedback loop with mir-144 (PubMed:33833125, PubMed:18941117). May coordinate repression of genes controlling myocardial differentiation and mitochondrial metabolism with positive modulation of cell proliferation genes (PubMed:33833125). Required for regeneration of the myocardium after injury, probably acting by stimulating renewal of preexisting cardiomyocytes in adult hearts (PubMed:33833125). Colocalizes with the cytosolic muscle marker troponin C. Expressed in cardiomyocytes. First expressed in the inner cell mass (ICM) of embryos at 18 hpf (hours post fertilization) and continues to be expressed in the developing embryo until at least 48 hpf (PubMed:18941117). Expressed in the developing hematopoietic system, at 24 hpf and circulating primitive erythrocytes at 48 hpf (PubMed:11535513, PubMed:18941117). Expressed in the pronephros, and in circulating definitive erythrocytes in the heart lumen and vessels of the tail at 8 dpf (days post fertilization) (PubMed:11535513). In adult heart myocardium upon injury (PubMed:33833125). Repressed in embryos by microRNA miR-144 (PubMed:18941117). Morpholino knockdown causes significant reduction in expression of embryonic alpha globin e1 hbae1.1 in 22 hpf (hours post fertilization) and 36 hpf embryos. Belongs to the krueppel C2H2-type zinc-finger protein family.