Fig. 4. Expression of Wnt ligands during cardiac morphogenesis. (A) Several Wnt ligands are expressed during early cardiac morphogenesis, as depicted at E9.5. This includes Wnt8a, which is expressed throughout the heart (red) (Jaspard et al., 2000; Kwon et al., 2007), Wnt2a and Wnt2b, which are expressed in the inflow tract and atria during development (yellow) (Monkley et al., 1996; Zakin et al., 1998), and Wnt5a and Wnt11, which are expressed in the outflow tract (green) (Schleiffarth et al., 2007; Zhou et al., 2007). (B-D) In situ hybridization shows the expression of Wnt2a (red) in a posterior-to-anterior gradient in an E9.5 mouse heart, with highest expression in the developing inflow tract (IF) and atria (A). V, ventricle.