Developmental dynamics of OSM development in zebrafish. In situ hybridisation for myf5 (A-D,G,J), myod (E,H,K,N), myog (F,I,L,O) and mylz2 (M), or MyHC immunodetection (P). Images are either dorsal view wholemounts with anterior towards the left (A,B,D,F,H,J,K,M), transverse cryosections with dorsal towards the top (C,E,G,I,L,N,O) or lateral view wholemounts with anterior towards left and dorsal towards the top (P). (A-C) At 30-38 hpf, myf5 is expressed in somites (white arrowheads), pectoral fin (green arrowheads) and bilateral patches anterior to the pectoral fins (red arrowheads). (D-I) By 48 hpf, myf5 expression had coalesced at the midline, forming a distinctive chevron structure (red arrowheads) that had begun expression of myod but not myog, and was associated with oesophageal tissue (red dots). The anterior hypaxial muscle anlagen expressed both myod and myog (yellow arrowheads). (J-O) At 72 hpf, expression in OSM region of myf5 was greatly reduced, myod increased and myog appeared strongly. Asterisks indicate hypobranchial muscle in pharynx. At 72 hpf, weak oesophageal mylz2 expression commenced (red arrowhead). (P) MyHC was detected in OSM (red arrowheads) at 78 hpf and extended posteriorly to somite 4 (green dotted lines). By 108 hpf, OSM (red dotted lines) had a distinctive funnel shape still extending from above SHM (yellow arrowhead) and PHM (white arrowhead) only to somite 4. Asterisks indicate hypobranchial muscles in pharynx. (Q) OSM morphogenesis and temporal onset of MRF gene expression from a dorsal view. Arrowheads indicate OSM (red), SHM (yellow), pectoral fin muscle (green) and PHM (white). e, eye; N, notochord; NT, neural tube; ov, otic vesicle.
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