Fig. 6. Heterotopic grafting experiments reveal head-specific cues for lateral rectus development. (A-E) Dorsolateral view of chick embryos whose somites at forelimb levels were replaced (A) orthotopically with quail somites or (B-E) heterotopically with quail pre-otic mesoderm. (F-J) Lateral view of the trigeminal area of chick embryos whose head mesoderm at the level of rhombomere 2 was (F) replaced orthotopically with quail head mesoderm or (G-J) heterotopically with quail somites from forelimb levels. Quail tissues were detected in brown, using the QCPN antibody, in addition to blue staining for Lbx1 (A,B,F,G), Pax7 (C,H), Paraxis (D,I) and Myf5 (E,J). Note that orthotopic grafting results in normal marker gene expression (A,F, arrows). Heterotopic grafting of head mesoderm into the trunk prevents marker gene expression, indicating that the graft is deaf to signals that pattern the somite (B-E, arrowheads). Somites transplanted into the head express Pax7 (H), paraxis (I) and Myf5 (J) in a segmented fashion (arrows) with Lbx1 always absent (G, arrowheads). Thus, the ectopic somites show marker gene expression reminiscent of the epaxial half of the somite. hy, hyloid arch; ov, otic vesicle; ma, mandibular arch; sc, spinal cord; som, somites. Scale bar: 200 µm.
