Figure 3: Dextral looping bias in sfw mutants occurs independently of Nodal activity or KV function.

(a) Analysis of looping direction in wild-type (wt) embryos or sfw mutants treated with the Nodal inhibitor SB431542. Wild-type embryos treated with SB431542 show a significant reduction in the number of d-looped hearts when compared with dimethyl sulphoxide (DMSO)-treated controls. However, no significant reduction in the number of d-looped hearts is observed in sfw mutant embryos treated with SB431542 when compared with DMSO-treated controls; n=7 clutches of embryos. (b) Analysis of looping direction in wt embryos and sfw mutants, injected with either a uas:gfp control or injected with uas:lft1 and heat-shocked at 14 hpf (8–10 somite stage). Wild-type embryos overexpressing uas:lft1 showed a significant reduction in the number of d-looped hearts when compared with uas:gfp-injected controls. No significant reduction in the number of d-looped hearts was observed in sfw mutants injected with uas:lft1 when compared with uas:gfp-injected controls. uas:gfp data n=4 clutches of embryos, uas:lefty1 data n=7. (c) Analysis of looping direction in wt embryos, sfw mutants, dnaaf1 mutants and sfw/dnaaf1 double mutants. sfw mutants show a significant reduction in the number of d-looped hearts when compared with wild-type embryos. Dnaaf1 mutants show a significant reduction in the number of d-looped hearts when compared with either sfw mutants or wild-type embryos. sfw/dnaaf1 double-mutant embryos show a significant reduction in the number of d-looped hearts when compared with sfw mutants or wild-type embryos; however, there is no significant reduction when compared with dnaaf1 single mutants. Sfw mutants, dnaaf1 mutants and sfw/dnaaf1 double mutants all have significantly more dextral looped hearts than sinistral or non-looped hearts; n=10 clutches of embryos. (a–c) Error bars indicate s.e.m. Significance determined by Student’s t-test indicated by asterisks: *P<0.05, **P<0.01, ***P<0.005.