<i>Ring1b</i> mutants lack almost all head cartilage elements.

<p>Lateral view of WT and <i>ring1b</i> live embryos at 72 hpf (A, B). Alcian-Blue stained head cartilages of WT (C, E, G and H) and <i>ring1b</i> (D, F, H and J) mutants at the indicated developmental points, ventral views. The paired trabeculae have elongated and fused posteriorly in WT embryos at 56 hpf (E) and by 72 hpf the elaborate cartilagenous skeleton of the head has been established (I). In contrast, no cartilage is visible in <i>ring1b</i> mutants except for two minute cartilage deposits at 72 hpf <i>ring1b</i> mutants (J: arrowheads). ch: ceratohyal; ep: ethmoid plate; hys: hyosymplectic; m: Meckel’s cartilage; pc: parachordal, pq: palatoquadrate; tc: trabeculae.</p

Loss of endochondral and dermal ossification in <i>ring1b</i> mutants.

<p>Ventral (A–D, E, F) and lateral (A’–D’, E’,) views of <i>in situ</i> hybridizations with riboprobes against the indicated genes in WT and <i>ring1b</i> mutants at 68–72 hpf. In WT embryos, <i>runx2a</i> and <i>runx2b</i> are expressed in hypertrophic pharyngeal arch-derived chondrocytes, as well as in the dermal ossification centers of the operculum, parasphenoid and cleithrum. Weak expression is detected in pharyngeal arches and the parasphenoid of <i>ring1b</i> mutants (B, B’, D, D’). At 72 hpf, <i>col10a1</i> is expressed in developing dermal bones in WT embryos, but not in <i>ring1b</i> mutants (E–F). cl: cleithrum; de: dentary; h: hyoid; m: mandibular; mx: maxilla; pa: pharyngeal arches; pq: palatoquadrate; ps: parasphenoid, op: operculum cl: the cleithrum. Numbers indicate the respective pharyngeal arches.</p