Fig. 6: Embryonic origins and environment of the zebrafish pectoral girdle.

a Four embryonic populations reside at the prospective pectoral girdle region at the 10–12 somite stage. They establish the embryonic head/trunk interface in the zebrafish embryo by the pharyngula stage. b Schematic drawing of the left pectoral region of a zebrafish larva. Based on its embryonic origin, each element follows the same color code as in (a): somites-derived, pink; fin-field LPM-derived, yellow; CPM-derived, green; branchial neural crest cell-derived, light blue. The anterior somites contribute to pectoral muscles and dorsal cleithrum. The branchial neural crest cells contribute to ceratobranchial cartilages and anterior ridge of the cleithrum. The CPM gives rise to mesenchymal cells surrounding the cleithrohyoid muscle and is mosaically distributed throughout the cleithrum. The fin-field LPM forms the posterior half of the cleithrum. The scapulocoracoid and endochondral disc originate exclusively from the fin-field LPM. The oval cells surrounding the bone matrix of the cleithrum represent osteoblasts. The distal portion of the pectoral fin elements and the posterior portion of the posterior hypaxial muscle is partially removed (cut surfaces are shaded). ab abductor muscle, ad adductor muscle, bncc branchial neural crest cells, cb ceratobranchial, cle cleithrum, CPM cardiopharyngeal mesoderm, ed endoskeletal disc, gp posterior lateral line ganglion, gX vagus ganglia, ie inner ear, m myotomes, opv optic vesicle, otv otic vesicle, phy posterior hypaxial muscle, sc scapulocoracoid.