Fig. 9

Altered ultrastructure of mitochondria in col6a1^ama605003 mutant fish myofibers.

TEM pictures of sagittal sections of muscles from wild type (WT, A1-4), heterozygous (HT, B1-4) and homozygous (HM, C1-4) col6a1^ama605003 mutants, at 2 dpf (A1, B1, C1), 3 wpf (A2, B2, C2), and 4 mpf (A3-4, B3-4, C3-4). In WT, the mitochondria constantly exhibited a dense and well-delineated lamination of the inner membrane and a well-defined outer membrane (A), attesting of the good quality of the fixation-inclusion procedures. In HT and HM muscles, the morphology of mitochondria was diversiform. Similarly to observations in Figs 7 and 8, some mitochondria presented a matrix partly cleared, or even devoid, of electron dense material (B, C arrow) and with severely dilated external membrane detached from the inner condensed membrane (B2-3, C3-4, arrows). These abnormalities were often associated with figures of vacuole/autophagic vesicles (C2, C4, asterisk). In the same area of HT or HM sections, we often observed a normal mitochondrion close to another one exhibiting either swollen cristae (B4, C4, arrows), or even cristae reduced to a few vesicles (B1-2, C2). In a few mitochondria the cristae were even ultra-condensed to a dense core separated from the outer membrane by a vesicle (arrows, B3.1–2, C1). The abnormal mitochondria most often bounded the limits between the crystal-like organized (o) and disorganized (d) myofibrils.