Fig. 2. The pac mutation affects cell-cell adhesion in the midbrain-hindbrain region. (A-C) Bodipy ceramide staining; 24 hpf; confocal microscopic cross sections at hindbrain levels; (A) wild-type sibling, (B,C) pac^fr7 mutant. Red arrowheads indicate rounded cells, blue arrows indicate ectopic rosette-like structures in dorsal regions of the pac mutant, and white arrows indicate ventricle lumen of the neural tube and ectopic lumina in dorsal rosette-like structures in pac. Insets in A,B show longitudinal sections through the mid- and hindbrain. The midbrain-hindbrain boundary (mhb) is indicated by white arrowheads and levels at which the cross-sections are taken are indicated by white arrows. Note the less pronounced mhb in pac mutant (B). (D-K) Chimeric embryos after transplantation of wild-type or pac mutant cells into wild-type or pac mutant hosts, as indicated: 24 hpf; lateral view of the mid- and hindbrain (D-F) and transverse sections at midbrain-hindbrain level (G-K). Note the tighter organization of the aggregate in I compared with K. Arrows in E,F,J,K indicate isolated cells. Note that in K, isolated pac mutant cells have a rounded shape, in contrast to their elongated wild-type neighbors (compare with alar wild-type cells in G).

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