Fig. 6

Treatments to block definitive hematopoiesis ablate the trunk hematopoietic clusters, but have less affect upon tail hematopoiesis. Panels show paired DIC and GFP fluorescence images of 4 dpf scl-PAC-GFP transgenic embryos. The lumens of the major vessels are indicated as in Fig. 4. Panels A, C, and E are lateral views in the mid-trunk, centred on a somite boundary. Panels B, D, and E show the ventral tail. Panels A and B show a control embryo from a TCDD experiment, treated with vehicle (0.1% DMSO) alone. Panels C and D are an embryo treated with 6 ng/ml TCDD at 12 hpf. Panels E and F are an embryo injected with 2 ng of a splice-blocking antisense morpholino oligonucleotide (MO) targeted to runx1. (A) A typical trunk hematopoietic cluster consisting of approximately 15 GFP-expressing round cells. Interestingly, this cluster is associated with one of the transient vessels that link the DA and PCV at this time (Isogai et al., 2001). This is the case for some, but not all, of the hematopoietic clusters at this stage. (B) The tail contains many hematopoietic cells, predominantly associated with the roof of the CV. (C) In embryos treated with TCDD, the formation of trunk hematopoietic clusters is ablated. In this embryo, only one GFP-expressing cell with round morphology was seen (arrow). All other GFP-expressing cells between the DA and PCV have disorganized endothelial morphology. (D) In the tail of TCDD-treated embryos there is a slight increase in GFP-expressing cells having endothelial morphology and a slight decrease in cells with hematopoietic morphology. However, plentiful hematopoietic cells are still detectable. (E) In runx1 MO-injected embryos, trunk hematopoietic clusters are completely ablated. Endothelial cell morphology was normal, but, interestingly, the separation of DA and PCV is reduced. (F) In the tail of runx1 MO-injected embryos, the number of GFP-expressing hematopoietic cells is marginally reduced. Endothelial morphology is apparently unaffected.