Contributions of VEGFR and hematopoietic marker Gata1 in FGFR-mediated effects. (A-H) Specific inhibition of VEGFR pathway by SU5416 does not affect ρ (E) or Lmo2 (H) expression and slightly up-regulates Vegfr2 (F) and Ets1 (G) compared with their respective controls (A,D,B,C). (I-M) Gata1 expression at HH4 (Ii-ii), 6 (Ji-ii), 7 (K), 8 (L), and 10 (Mi-ii). Arrowhead points to weak but broad expression in EEM. Sections of panels Ii, Ji, and Mi at indicated levels are shown in Iii, Jii, and Mii, respectively. (N-R) Control bead does not affect Gata1 expression (N-O), which at HH10 is up-regulated in blood and absent in nonblood cells (Mi-ii). FGF4 bead maintains low-level expression of Gata1 in adjacent cells (P-Q and section in R). These cells are completely negative for ρ (Figure 3F). Dotted line marks bead and arrow points to weak expression. (S-V) SU5402 treatment of whole embryo results in up-regulated and expanded Gata1 expression (T,V) compared with control (S,U), similar to the effect on ρ globin (Figure 4L).