(A–D) Dorsal views of 22–24 somite embryos showing lefty1 in the brain and (A′-D′) different focal plans showing lefty1 in the brain and lefty2 in heart field within the same embryo. Uninjected embryos showing normal left-sided expression of lefty2 in the heart field (green arrows) of both DMSO control embryos and SU5402 treated embryos (A, A′, B, B′). In contrast, bilateral lefty1 expression (yellow arrowhead) in the brain of SU5402 treated embryos in comparison to the normal left-sided expression (green arrowhead) of lefty1 in the DMSO control embryos (A, A′, B, B′). spaw MO injected embryos treated with either DMSO or SU5402 show absence of lefty2 expression in the heart field (blue arrows; C, C′, D, D′). However, SU5402 treated embryos still exhibit bilateral expression of lefty1 in the brain whereas DMSO control embryos no longer express lefty1 (blue arrowhead; C, C′, D, D′). (E) Histogram indicating percentages of embryos displaying normal (left-sided), reversed (right sided), absent and bilateral heart expression patterns of lefty1 for uninjected DMSO control embryos, uninjected SU5402 treated embryos, spaw MO injected DMSO embryos, and spaw MO injected embryos treated with SU5402. (F) Histogram indicating percentages of embryos displaying normal (left-sided), reversed (right-sided), absent and bilateral brain expression patterns of lefty2 for WT DMSO control embryos, WT SU5402 treated embryos, spaw MO injected DMSO embryos, and spaw MO injected embryos treated with SU5402.