Fig. 3. Comparison of spaw with lefty2 and pitx2. (A,C,D) Dig-spaw (purple) + DNP-lefty2 (red) probes. Dorsal close-up; A is at a lower magnification than C and D; lefty2 marks the heart field. (A,C,D) The patterns seen in embryos from a pool of 20-23 somite embryos. (A) spaw is expressed in this embryo but lefty2 is not. The converse pattern (lefty2+,spaw–) was never seen. (B) Dig-spaw probe alone, 20-23 somite stage. Dorsal close-up near heart field. Comparison of B (spaw probe) with C (spaw + lefty2 probes) emphasizes the extensive overlap between the left-sided spaw and lefty2 expression domains in C. (D) Asymmetric spaw and lefty2 zones are present as largely non-overlapping domains. (E) Dorsal close-up. DNP-lefty2 probe (red) only, 20-23 somite embryo. (F) Twenty to 23 somite embryo. Dig-spaw (purple) + DNP-pitx2 (red) probes. Lateral view, anterior towards the left, comparing the anterior border of spaw (black arrowhead) in the lateral plate with the anterior position of left-sided pitx2 (arrow) in the diencephalon.