Figure 4

Early anatomy of zebrafish endochondral growth zones. (A) Endochondral growth zones start to appear in the zebrafish skeleton around 12days post-fertilization (dpf). One or more ossification centers appear on each bone. Unossified cartilage regions at bone ends become unidirectional growth zones, while those flanked by ossifying cartilage become bidirectional growth zones. In the 12dpf pharyngeal skeleton, the QA and MP bones ossify over the PQ cartilage, the HM and SY bones ossify over the HS cartilage, the HH, CH and EH bones ossify over the CH cartilage, BB1 and 2 ossify over the BB cartilage. Single ossifications appear on other pharyngeal bones. (B) In the caudal fin endoskeleton, single ossifications appear on each cartilage element, resulting in a single distal endochondral growth zone per element. (C) In the pectoral fin endoskeleton, the endoskeletal disc is progressively carved into four proximal- and seven distal radials. Ossification of each proximal radial leaves a single endochondral growth zone at the distal end. Distal radials do not ossify. BB, basibranchial; BH, basihyal; CB, ceratobranchial; CC, compound centrum; DR, distal radial; ED, endoskeletal disc; H, hypural; HB, hypobranchial; IH, interhyal; MC, Meckel’s cartilage; NO, notochord; PH, parhypural; PHB, pharyngobranchials; PR, proximal radial; SCO, scapulocoracoid, VHH, ventral hypohyal.