Fig. 1

Comparison of scxa and scxb expression during embryonic and juvenile stages. In situ hybridization for indicated genes shown in lateral (C–J) or ventral view (A, B, K–M). A, B) At 72 hpf, scxa is detected in Meckel’s adductor tendon (mat), the intermandibularis tendon (imt), the mandibulohyoid junction (mhj), the sternohyoideus tendon (sht), and hyohyoideus junction (hhj). scxb is expressed at the sht and hhj, the mat, and the ocular muscle tendons (ots). C, D) At 72 hpf, scxa and scxb are expressed weakly at the myosepta (blue arrowheads) and the caudal fin (black arrows). E–J) In situhybridization for scxa (E–G), sox9a (H), and scxb (I, J) at juvenile stages as indicated, showing expression in the trunk in the posterior vertical myosepta (arrowheads), and the more anterior myosepta near the thoracic ribs (arrows), intermuscular bones (white arrowheads), fin radials (blue arrowheads), in gills (blue asterisk), and between fin bony ray segments (purple arrowheads). Sagittal sections in rib area (E′) and myosepta in anal fin area (E″) show scxa staining in intramuscular tendons separated from muscle fiber (mf) ends (yellow arrowheads) by an unstained tendon-sheath or ECM (brackets). K–M) scxa expression at juvenile stages in head tendons, including protractor hyoideus tendons (orange arrow) and intermandibularis anterior tendons (green arrows), at the attachments of the cranial muscles (labeled with tnnc) (L): Protractor hyoideus-dorsal and ventral (pr-h) and the intermandibularis anterior (ima). No scxb expression is detected in cranial tendons at juvenile stages. Scale bars, 100 µm (A–D, E′, E″), 0.5 mm (E–M).