Fig. 4. Expression patterns of zebrafish tfr1a and tfr1b during embryogenesis. Whole-mount RNA in-situ hybridization for tfr1a (B,E,H) shows an expression pattern restricted to the hematopoietic intermediate cell mass and later circulating blood, identical to that of ße1 globin (A,D,G), shown at 15 somites, 20 hpf, and 36 hpf. By contrast, the expression of tfr1b (C,F,I) at these timepoints is ubiquitous.