Effect of morpholino knockdown of transferrin-a or TfRs on o-dianisidine staining for hemoglobin at 48 hpf. Uninjected embryos (A) exhibited normal levels of hemoglobin, while morpholino knockdown of transferrin-a via injection of trf-MO1 (B) targeting the ATG, or trf-MO2 (C) targeting the exon 4 donor, or coinjection of trf-MO1/trf-MO2 (D) produced anemia. In contrast, coinjection of mismatch controls trf-MO1M/trf-MO2M (E) failed to produce anemia. Morpholino knockdown of the erythroid-specific transferrin receptor (TfR1a; F) resulted in anemia, while knockdown of the ubiquitously expressed transferrin receptor (TfR1b; G) or TfR2 (H) did not cause anemia. The scale bar represents 200 μm.