Cooperative contributions of the klf1 and klf17 genes in zebrafish primitive erythropoiesis

Krüppel-like transcription factors (Klfs), which are characterized by the three conserved C-terminal zinc fingers, are involved in various biological processes, such as haematopoiesis and angiogenesis. However, how the Klf family of transcription factors cooperate in organogenesis remains elusive. During zebrafish embryogenesis, both klf1 and klf17 are expressed in the intermediate cell mass (ICM), where primitive erythroid cells are produced. Using CRISPR–Cas9 genome editing technology, we established klf1-klf17 double mutant zebrafish to investigate the functionally interactive roles of the klf1 and klf17 genes. The klf1-klf17 mutant exhibited a diminished number of circulating primitive erythroid cells at 2 days postfertilization (dpf), while klf1 or klf17 single mutants and wild-type embryos produced comparable numbers of primitive erythroid cells. Circulating erythroid cells from the klf1-klf17 mutant possessed larger nuclei at 2 dpf than wild-type cells, suggesting the impairment of primitive erythroid cell maturation. The expression of the erythroid cell maturation markers band3 and mitoferrin, but not the haematopoietic progenitor markers c-myb and scl, was decreased in the klf1-klf17 mutant at 1 dpf. Thus, these results illustrate the cooperative function of klf1 and klf17 in the maturation processes of zebrafish primitive erythroid cells.