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Koibuchi N
,
Taniyama Y
,
Nagao K
,
Ogihara T
,
Kaneda Y
,
Morishita R
.
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Vascular endothelial growth factor (VEGF) is known to play an essential role in vascular development. We have overexpressed VEGF122 or VEGF170, which are equivalent to mouse VEGF120 and VEGF164, in developing Xenopus embryos. Overexpression of VEGF170 but not VEGF122 demonstrated an absence of expression of hematopoietic markers alpha-globin and GATA-1 but only in the posterior portion of the blood island. Interestingly, strong signals of endothelial markers, msr, fli-1, and tie-2, were detectable in those regions, instead of hematopoietic markers. These results suggested both that injection of VEGF170 resulted in disturbance of vasculogenesis in the posterior portion of the blood island, with excessive production of endothelial cells at the expense of blood cells, and that the anterior and posterior portions of the VBI may have distinct characteristics.
Fig. 1. Edema induced by overexpression of VEGF122 or VEGF170. Tadpoles injected with (A,B) LacZ mRNA, (C,D) VEGF122 mRNA or (E,F)
VEGF170 mRNA. (A, C, and E) Lateral views of stage 42 embryos. (B, D, and F) Ventral views of stage 46 embryos. Yellow arrowheads indicate beating
heart. Red blood cells are visible in the heart of a control tadpole injected with LacZ mRNA (B), but are rare in tadpoles injected with VEGF122 or
VEGF170 mRNA (D,F). Blue arrowheads indicate pooled blood cells.
Fig. 2. Expression pattern of hematopoietic markers (a-globin and GATA-1) and endothelial markers (tie-2 and msr) shown by in situ hybridization.
Embryos injected with (A, D, G, J, and M) LacZ, (B, E, H, K, and N) VEGF122 or (C, F, I, L, and O) VEGF170 mRNA into dorsal-vegetal blastomeres.
(A–C and G–I ) Lateral views of embryos. (D–F, J–L, and M–O) Ventral views of embryos. (A–F) Expression pattern of a-globin and tie-2. (G–L)
Expression pattern of a-globin and msr. Yellow arrowheads indicate vascular hyperperfusion in vitelline venous network. Green arrowheads indicate
intersomic veins. Red arrowheads indicate ectopic expression of endothelial markers, but not hematopoietic marker. (M–O) Expression pattern of
GATA-1. Black arrowheads indicate absence of expression of GATA-1. Anterior is right for all embryos.
Fig. 3. Expression pattern of a-globin in embryo lineages traced with LacZ mRNA. Embryos were injected with LacZ mRNA into (A) two dorsal-vegetal
or (B) ventral-vegetal blastomeres at the 8-cell stage. Embryos were co-injected with LacZ and VEGF170 mRNA into (C) two dorsal-vegetal or (D) ventralvegetal
blastomeres at the 8-cell stage.
Fig. 4. Expression pattern of tie-2, fli-1, and msr in stage 26/28 embryos shown by in situ hybridization. Embryos were injected with either (A, C, and E)
LacZ mRNA or (B, D, and F) VEGF170 mRNA into dorsal-vegetal blastomeres. Expression pattern of (A,B) tie-2, (C,D) fli-1, and (E,F) msr. Red
arrowheads indicate ectopic expression in the posterior portion of the prospective VBI.
