Activation of Wnt signaling ablates lefty2 expression in the heart without affecting the left-sided expression of spaw and pitx2. (A-P) Representative images of spaw expression in LPM (arrowheads in A-C,I-L), lefty2 expression in the cardiac field (arrows in E-G,I-K), and pitx2 expression in the posterior LPM (asterisks in M-O). Shown are dorsal views, with anterior to the top of 22- to 24-somite staged embryos. A tropomyosin probe was included in in situ hybridization to ensure embryos were at the proper stage, with the exception of pitx2 staining. (Q) Quantification of the percentages of asymmetric expression of spaw, lefty2 and pitx2. s, spaw; l, lefty2; p, pitx2. L, left side; A, absence; R, right side; B, bilateral; n, total numbers of embryos scored.