Figure 5

(A) Lhx9 α/β and Lhx2 , but not Lhx9-HD are expressed in the septum transversum in mice at E9.5. Whole-mount in situ hybridization with anti-Lhx9α/β (top panels) and Lhx2 (middle panels) RNA probes detect a strong Lhx9α/β expression in septum transversum both in the control (left panels, arrow) and the Fog2^-/- embryo (right panels, arrow); an Lhx9-HD RNA probe does not show the expression of this isoform in the septum transversum (bottom panels); hindlimb bud expression is indicated by an arrowhead. The higher magnification of STM expression for Lhx9α/β is shown in insets (top panels). (B) The myocardial Fog2 does not suppress Lhx9α/β expression in the heart. Whole-mount staining of the E14.5 hearts with the anti-Lhx9α/β RNA probe. The wild-type sample is on the left and the αMhc-Fog2/Fog2^-/- heart is on the right. At this stage Lhx9α/β expression is extinguished in the wild-type heart (left) (also Fig. 2B) while the Fog2 mutant sample with the myocardial-restricted expression of Fog2 (right) remains strongly positive for Lhx9α/β expression.