Figure 5. Overexpression of Wild-Type tif1γ mRNA or Marrow Transplantation Rescues Embryonic Hematopoiesis in mon Mutants.

(A) mon^tg234 mutants are rescued by injection of mRNA-encoding wild-type Tif1γ protein. At 4 d of development, large numbers of RBCs are visible in the circulation of wild-type zebrafish, shown here by o-dianisidine staining of hemoglobin. Uninjected mon^ttg234 homozygous mutants are completely bloodless. Injection of 100 pg of wild-type tif1γ mRNA rescues erythropoiesis in mutant embryos. o-dianisidine-stained larvae are shown in ventral views to highlight blood in vessels.

(B) Transplantation of wild-type zebrafish marrow cells carrying a gata1:GFP transgene into 2-d-old embryos reconstitutes erythropoiesis, but not viability, in mon^tg234 homozygous mutants. Still frames from movies of live embryos at day 3 posttransplant highlight less than 100 GFP⁺ RBCs in circulation (top). Transplanted cells were observed to proliferate resulting in thousands of donor-derived erythrocytes 7 d later (bottom). Arrows indicate the hearts of control and transplanted zebrafish. See Videos S1–S4.