Fig. 2. Myotome alterations in XHas2-Mo injected embryos. All embryos are at stage 28-30 and are visualized by the expression of CA (A,A') and by 12/101 immunoreactivity (B,B',C,D). Red-gal staining identifies the injected side of the embryos. (A) Bending of the embryos was observed in the injected side. (A') Example of a mild class phenotype embryo; the myotome arrangement is altered in the injected side of the embryo (arrow). (B) Lateral view of the control side of a representative case of a severe class phenotype at stage 26 (arrowheads indicate the somites). (B') Injected side of the embryo in B showing a complete disruption of somites segmentation, as indicated by the arrowheads and a strong reduction in the 12/101-positive cells (compare double-headed arrows in B and B'). Red spots on the head and trunk region (Red-gal staining) identify the site of injection. (C-D') Two representative cases of severe class phenotype embryos, longitudinally sectioned and stained with Hoechst to visualize the nuclei (C',D'). (C,D) The pattern of the 12/101 positive myocytes is altered within the somites in the injected side (arrows).