Fig. 10.

Model for growth zone establishment in the zebrafish ceratohyal cartilage. (A-C) Diagram of GZ development in a single ch cartilage on one side of the head as chondrocytes condense (A), differentiate (B) and begin to proliferate (C); ventral to the left. (A) Pthlha-expressing cells (green) are first detected at either end of the developing cartilage condensation at 48-66 hpf. (B) Entpd5a-expressing cells (red) are first detected near the center of the differentiating chondrocyte stack at 66-72 hpf, correlating with the onset of cranial muscle contraction (black arrows). (C) A mature GZ including Ihha expression (blue) acting in opposition to Pthlha (green); cartilage proliferation (gray doublets) and a distinct perichondrium (gray margin) emerge after 96 hpf.