Fig. 1

Cells with satellite cell features are present in adult zebrafish skeletal muscle. (A-B) Transmission electron microscopy (TEM) on adult zebrafish tail skeletal muscle from slow-twitch (A-A’’) and fast-twitch (B-B’’) muscle fiber domains. (A) TEM of slow muscle reveals mitochondrial-rich muscle fibers (mustard arrow points to a cluster of dark gray mitochondria), putative satellite-like cells (SLCs; white arrowheads), and myonuclei (MN; blue arrowhead points to a myonucleus). (A’) Higher magnification view of a SLC containing dense heterochromatin (white arrowhead) and surrounded by basal lamina (red arrow). (A’’) A myonucleus (MN; blue arrowhead) located within the muscle fiber membrane. Myonuclei are characterized by a lack of dense heterochromatin and often by a prominent nucleolus (orange arrow). An adjacent myofibril is indicated by a blue arrow. (B) TEM of fast muscle reveals fewer mitochondria, a putative SLC (white arrowhead), as well as myonuclei (MN, blue arrowheads). (B’) Higher magnification view of a SLC containing dense heterochromatin (white arrowhead) and surrounded by basal lamina (red arrow). (B’’) A myonucleus (MN; blue arrowhead) located within the muscle fiber membrane shows similar characteristics to slow muscle myonuclei. (C-C’’’) Pax7-positive cells (red; white arrowheads) are localized within the basal lamina of adult zebrafish skeletal muscle (anti-Laminin in green) (inset shows enlarged view of Pax7-positive cell). DAPI labeling confirms Pax7 localization in nuclei. (D-D’) Pax7-positive cells (red; arrowheads) are located outside of the muscle fiber membrane, marked by a Dystrophin FlipTrap transgenic line. (D’) Magnified view of boxed region in D. Scale bar in A, B is 2 µm, in A’, A’’, B’’ is 1 µm, in B’ is 500 nm, and in C and D is 30 µm.