Figure 6. gfi1aa and gfi1b function at different hierarchical levels in hematopoietic epistasis.

(A) The ICM expression of gfi1aa and gfi1b was evaluated in mutants with genetic blocks at sequential stages in hematopoiesis at the 20 ss. (a–b) Both gfi1aa and gfi1b are expressed in the ICM (arrowheads) in wild type embryos. (c–d) Mutants with genetic defects at the hemangioblast level (clo) and hematopoietic progenitors (scl) specifically lack ICM expression of either gfi1aa or gfi1b. Note that the neural expression of the gfi genes is preserved in these genetic mutants, confirming the specificity of the assay. (g–h) ICM expression of gfi1aa is preserved in the gata1 mutant, vlt, whereas gfi1b expression is deficient. (i–j) In contrast, both gfi1aa and gfi1b are expressed in the ICM of the mfrn1 mutant, frs. (B) To confirm the presence of hematopoietic progenitors in various genetic mutants, the expression of lmo2 and gata2 was evaluated in mutant embryos at the 20 ss. (a–b) Both lmo2 and gata2 are expressed in the ICM of wild type control embryos. (c–d) Neither lmo2 nor gata2 is expressed in the ICM of clo mutants, which fail to specify hematopoietic and vascular progenitors. (e–h) Expression of lmo2 and gata2 is preserved in scl and gata1 (vlt) mutants, confirming that hematopoietic progenitors are present. (C) The AGM expression of ikaros, gfi1aa and gfi1b was evaluated in runx-1 mutants at 36 hpf and embryos were genotyped for runx-1 wild type and mutant alleles. ikaros was included as a reference control. (a–b) AGM expression (brackets) of ikaros is silenced in runx-1 mutants relative to wild type embryos (wt), confirming the defect in definitive hematopoiesis. (c–d) AGM expression of gfi1aa is preserved in runx-1 mutants. (e–f) Loss of runx-1 silences expression of gfi1b in the AGM.