Gfi1.1 regulates hematopoietic lineage differentiation during zebrafish embryogenesis

Growth factor independence 1 （GFI1） is important for maturation of mammalian lymphocytes and neutrophils and maintenance of adult hematopoietic stem cells （HSCs）. The role of GFI1 in embryonic hematopoiesis is less well characterized. Through an enhancer trap screen and bioinformatics analysis, we identified a zebrafish homolog of Gill （named grill） and analyzed its function during embryonic development. Expression of both an endogenous griLl gene and a GFP reporter gene inserted near its genomic locus was detected in hematopoietic cells of zebrafish embryos. Morpholino （MO） knockdown of gill.1 reduced expression of scl, Imo2, c-myb, mpo, ragl, gatal and hemoglobin alpha embryonic-1 （hbael）, as well as the total amount of embryonic hemoglobin, but increased expression ofpu.1 and l-plastin. Under the same conditions, MO injection did not affect the markers involved in vascular and pronephric development. Conversely, overexpression of gill.1 via mRNA injection enhanced expression ofgatal but inhibited expression ofpu.1. These findings suggest that Gill.1 plays a critical role in regulating the balance of embryonic erythroid and myeloid lineage determination, and is also required for the differentiation of lymphocytes and granulocytes during zebrafish embryogenesis.