Fig. 5. CNC cells influence paraxial mesoderm migration and axial registration in chick embryos. (A) An image of a stage 8 embryo injected with DiI in the CPM (arrow indicates dye location, dorsal view). (A') A lateral view of the embryo in A after 48 hours; arrowhead points to the labeled cells migrating toward BA1. (B,B') DiI labeling of the CPM in CNC-ablated embryos. In some ablated embryos cell migration was arrested (n=8/13) whereas in others partial migration towards BA1 was observed (n=4/13) compared with normal migration of CPM cells in controls (n=13/14). (C-D') Embryos were labeled with both DiI and DiO simultaneously (DiO, green, arrowheads in C and D; DiI, red, arrows in C and D). CPM cell migration was monitored after 48 hours. A mixture of the DiO- and DiI-labeled cells streaming toward BA1 is seen in the ablated embryo (D', n=6/8) compared with the separate streams seen in controls (C', n=4/5). Ablation boundaries are marked by broken line. (E-H'') Quail-chick (Q-C) transplantation assay; E, a scheme of the experiment. Stage 8 quail CPM grafts labeled with DiI at the level of rhombomere 4 and then transplanted into stage-matched chick embryos. (F) A lateral view of the Q-C chimeric embryo after 24 hours. (F'-F'') Transverse sections through the BAs of the embryo on the left (F', ba1, F'', ba2) stained with the quail-specific antibody (QCPN, in green). Note the quail-derived cells exclusively in BA2 (F'', higher magnification in the inset, n=4/4). (G-H'') Similar images as shown in E-F'' except that the host chick embryo was CNC ablated. In the CNC-ablated embryo, quail-derived cells are seen in BA1 (arrows in H', inset, n=3/4) but not in BA2. Lateral views of embryos (A',B',C',D',F,H) are shown as an overlay of bright field and fluorescence images. ec, ectoderm; ht, heart; nt, neural tube; ov, otic vesicle; ph, pharynx. Scale bars: in A, 0.4 mm for B,C,D; in A', 0.5 mm for B',C',D'; in F, 0.36 mm for H; in F', 0.2 mm for H' and 0.1 mm for F'',H''.