Fig. 6. Cellular and molecular analyses of cranial paraxial mesoderm en route to the heart. (A) Diagram of a stage 16 embryo (ventral view), following removal of the heart. Dotted lines represent the three section levels displayed in the lower panels. (B) Diagram of quail-chick chimera assay. (C-I) Transverse sections at the first branchial arch (ba) level (upper dotted line in A). (C1-I1) Transverse sections at the aortic sac level (middle line). (C2-I2) Transverse sections at the outflow tract (OFT) level (lower line). (C-C2) Sections of CM-DiI-labeled cells at the aforementioned levels. (D-D2) Transverse sections through the quail-chick chimera, followed by immunostaining with the quail-specific antibody (QCPN, x10 bright field and fluorescence images) (D'-D2') x20 fluorescence images of the marked area shown in the x10 images (D-D2). (E-E2) Immunostaining for Myosin heavy chain using MF20 antibody. (F-I2) Sections through embryos subjected to whole-mount in situ hybridization with the indicated markers. aaa1, aortic arch artery 1; aaa2, aortic arch artery 2; as, aortic sac; ba1, ba2, first, second branchial arches; end, endocardium; myo, myocardium; nt, neural tube; ov, otic vesicle; ph, pharynx.