Disorganized Cohnheim’s fields, swollen reticulum and altered mitochondria in col6a1ama605003 mutant fish muscle.
TEM pictures of transversal sections of muscle from wild type (WT, A1-3) and col6a1ama605003 heterozygous (HT, B1-3) and homozygous (HM, C1-3) mutants at 2 dpf, 3 wpf and 4 mpf. At 2dpf (A1, B1, C1), 3 wpf (A2, B2, C2) and 4 mpf (A3, B3, C3) in HT and HM mutants, we observed in a few muscle fibers, abnormal mitochondria with areas of the matrix devoid of electron dense material (B1-3, C1-3, arrows). In these myofibers, the abnormal mitochondria were often located in close contact with enlarged sarcoplasmic reticulum (B1-2, C1-3, arrowheads). The altered mitochondria often marked the limit between crystal-like organized (o) Cohnheim’s field and pathologic disorganized (d) myofibrils (B1-3, C1-2). In HM (C1), some fibers appeared more affected than in HT, with drastically disorganized (d) areas separated from organized myofibrils (o) with mitochondria having swollen cristae (C1-3, arrows). The sarcoplasm area of the more affected fibers appeared devoid of material (B3, C1-2, asterisks). (B3) In a few muscle fibers of HM, the reticulum appeared drastically dilated (asterisk) with numerous blebs or autophagic vacuoles localized nearby or within myofibrillar disarray foci (C2) that were also in close contact with mitochondria with enlarged cristae (C2-3, arrows). None abnormal mitochondrion, myofibril disorganization or enlarged reticulum was seen in WT (A1-3).