Fig. 4.

Spiba mRNA expression within the heart-forming region. (A–C) Wholemount in situ hybridization for myeloid spiba, ventral views of heart-forming region, at stage 27 (A), stage 29 (B) and stage 31 (C). Red triangle depicts position of forming myocardium (B and C). (D–F) Transverse sections through heart region of same embryos, with section planes depicted (A–C). Stage 27 (D), stage 29 (E) and stage 31 sections (F). To ease identification, the approximate position of the (myocardial) mesoderm has been artificially-darkened (E and F). NFR (D–F) nuclear counterstained. Scale bar = 100 μm. Sp, section plane; M, myeloid/macrophage; HF, heart field; Mc, myocardium; Ec, endocardium; VM, ventral midline; En, endoderm.