Fig. 3

Lineage tracing of the premandibular head cavities. a DiI was injected into the coelom of the prmc of a cat shark embryo at st. 25. At st. 31 (42 days postinjection: 42 dpi), the DiI-injected embryos were fixed and histologically examined. b-h″ Transverse sections cut through the dashed lines in (a) DiI-injected catshark embryos at 42 dpi. Sections (b) and (f) were each aligned with adjacent sections immunostained with anti-myosin heavy chain (MyHC) antibody (c′, d′, e’, g’, and h′), stained with Alcian blue (AB) (c′, d′, e’, g’, and h′), and hybridized in situ with a Scx antisense RNA probe (g” and h″). DiI-labeled cells (magenta) are found in muscle fibers of specific sets of extraocular muscles (superior rectus, medial rectus, inferior oblique, and inferior rectus muscles) but not in Scx-positive tendon progenitor cells at the attachment site of all rectus eye muscles (asterisks) or in the pila antotica (outlined by the dotted line). IO, inferior oblique muscle; IR, inferior rectus muscle; LR, lateral rectus muscle; MR, medial rectus muscle; SR, superior rectus muscle. Scale bars = 200 μm