Impaired formation of prechondrogenic condensations and abolished cartilage differentiation in ring1b mutants.
Ventral (A–J) and lateral (A′–J′) views of WT and ring1b mutants at 50 hpf stained with the indicated genes. Prechondrogenic condensation markers sox9a and sox9b are expressed in ring1b CNCs residing in pharyngeal arches 1 and 2, albeit the expression domain is smaller (A–D′). Similarly, the expression domain of CNC markers sox10 and dlx2a is reduced in ring1b pharyngeal arches 1 and 2 (E–H′). Expression of sox9a, sox9b and sox10 is not detected at the presumptive location of the trabeculae in ring1b mutants (B, B′, D, D′, F, F′). Col2a1 is expressed in WT trabeculae and pharyngeal arches I–II, but expression is abolished in ring1b mutants (I–, J′). Note that expression of col2a1, a marker for differentiating chondrocytes, is normal in the otic vesicles and parachordals of ring1b mutants. tc: trabeculae cranii; pc: parachordal; ov: otic vesicle. Numbers indicate the respective pharyngeal arches.