Figure 5

Mad3 is a new left-right determinant. (A) Single ventral left or ventral right blastomeres were injected with EngMad3 or Vp16Mad3 constructs and organ placement was scored at stage 45. Significant levels of heterotaxia were observed when embryos were injected with EngMad3 (left: 21%, n = 96, p < 0.001; right: 12%, n = 91, p = 0.005; control: Eng) or with Vp16Mad3 on the right side (17% n = 90, p < 0.001; 6% n = 127, p = 0.1, control: Vp16). (B) Embryos injected with EngMad3 or Vp16Mad3 were processed for in situ hybridization at stage 21 with a XNr-1 probe. XNr-1 misexpression was correlated with Vp16Mad3 injection (right injected embryos: 19% bilateral expression, n = 117; left injected: 5% bilateral expression, n = 105) and EngMad3 (left injected: 75% no expression, n = 74; right injected: 21% no expression, n = 93) if compared to control embryos (uninjected, 10% no expression, n = 103). (B') XNr-1 expression pattern characterized in EngMad3 or Vp16Mad3 injected embryos. I- Left expression indicated by the white arrow; II-right expression indicated by the gray arrow; III- Bilateral XNr-1 expression indicated by the two blue arrows; IV- Absence of XNr-1 expression as indicated by the two black arrows.