Fig. 10

Differential functions of sox9 duplicate genes in the morphogenesis and growth of chondrogenic crest. Confocal micrographs of the pharyngeal arches of wild type (A,A',E,E'), sox9a^- (B,B',F,F'), sox9b^b971 (C,C',G,G'), and sox9b^b971; sox9a^-. (D,D',H,H') animals stained with the vital dye, BODIPY-ceramide as described (Yan et al., 2002) to label interstitial spaces. Images are color reversed so cells appear white and interstitial spaces black: original images (A-H) have been psuedocolored (A'-H') to highlight arch features. (A-D') At 48 hours, prechondrogenic condensations of crest cells are seen in the first (blue) and second (yellow) arches. The adductor mandibulae muscle core (red) and first endodermal pouch (purple) are shown for reference. Prechondrogenic condensations are normal in both single mutants (B-C') and reduced in size in the double mutant (D,D'). (E-H') The same individual animals in A-D ' were imaged at 72 hours. In wild-type animals (E,E'), chondrocytes have arranged themselves into characteristic stacks and are easily visualized by their thicker cell matrix. First arch cartilages include Meckel's (m) and palatoquadrate (pq), and second arch cartilages include the hyosymplectic (hs) and ceratohyal (ch). As described in Yan et al. (Yan et al., 2002), in sox9a^- animals, crest condensations are present but fail to differentiate and undergo morphogenesis to form stacks of chondroctyes (F,F'). In contrast, in sox9b^b971 animals (G,G'), chondrocytes are greatly reduced in number, yet can still form small stacks (e.g. pq). The sox9b^b971; sox9a^- double mutants show an additive effect including both morphogenetic and growth defects: condensations are smaller in size and do not form stacks of chondrocytes. Total animals examined: n_wt=3, n_sox9a=1, n_sox9b=4, n_sox9a;sox9b=5. Scale bar: in I', 100 µm.