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Myomere organization in adult zebrafish, and the effects of cryoinjury of the caudal peduncle. a Left side: Schematic of the musculature displays metameric organization of somite-derived units, called myomeres. Each myomere consists of superficial muscle (red area), which comprises slow-twitch fibers, and profound muscle (brown area), which contain fast- and intermediate-twitch fibers, grouped together as fast muscles. The upper- and lower-most margins comprise longitudinal muscles, called supracarinal muscles, along the dorsal side (green) and infracarinal along the ventral midline (purple). Right side: Transversal section through the caudal peduncle shown as a schematic and F-actin staining (white). The horizontal septum separates the dorsal and ventral parts. The vertical septum separates the left and right sides of the body. Scale bar indicates 500 μm. b Coronal section through the caudal peduncle shown as a schematic and F-actin staining (white). Scale bar indicates 500 μm. c Schematic of the cryoinjury procedure shown from the ventral side of the fish. The cryoprobe was precooled in liquid nitrogen (LN2) and immediately placed on one side of the anesthetized fish for 6 s. At a specific time point after cryoinjury, fish were euthanized, and their caudal peduncles were collected for fixation. d AFOG histological staining of coronal sections at different days post-cryoinjury (dpci). The uninjured side is detected by beige staining of the muscle, whereas the cryoinjured tissue lacks this staining. Collagen is stained in blue. At 4 and 7 dpci, three to four myomeres of one side appear grayish/bluish, corresponding to the wound area. At the subsequent points, new myofibers emerge at the injured side. Scale bar indicates 500 μm. N = 4.
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