Runx1P1 is not required for primitive or definitive hematopoiesis. (A) RT-PCR confirms deletion of the first exon of runx1P1 in 24 hpf embryos injected with the runx1P1 splice MO at doses greater than 0.125 pmol. Markers of primitive erythropoiesis (B–D) and definitive hematopoiesis (E,F) are expressed normally in 18 hpf Runx1P1 morphants. (G–I) The development of EMPs expressing gata1, mpx, and pu.1 is also unaffected by Runx1P1 knockdown. (J–N) Injection of a runx1 runt domain MO targeting both isoforms did not affect expression of primitive or definitive hematopoiesis at 18 hpf. (O–Q) Expression of EMP markers is also unaffected by Runx1 depletion.