Fig. 6

The lack of collagen XV disrupts notochordal basement membrane and prevents normal muscle striation. Transmission electron micrographs of the notochord (A, B) and of the myotome of 48 hpf control (A, C, E) and morphant (B, D, F–I) zebrafish. (A) In wild type and in control embryos, basement membrane surrounding the notochord (no) is constituted by three different layers: a true basement membrane (bm, arrow), a dense fibrous layer (dl) that surrounds the notochord (black bar), and an outermost fibrous layer (ol) parallel to the notochord (white bar). (B) In Col15a1-MO embryos, the basement membrane is highly disorganized. In the dense fibrous layer (dl), collagen fibers are not properly arranged. The outermost fibrous layer (ol) is less dense and more diffuse compared to control. (C, E) In 48 hpf control embryos, myofibrils (my) are completely developed and the cytoplasm is overgrown with myofibrils. As observed in the longitudinal section (E) muscle striation is complete. (D, F–H) In Col15a1-MO embryos, the number of myofibrils (my) is low. Myofibrils are preferentially located in the cortical area of the cells (C) and often present an orthogonal arrangement (G). (F–H) Muscle striation (s) is more or less visible depending on the severity of the morphotype. (I) Multivesicular vesicles which represent a sign of muscle degeneration are observed. Bar: 2 μm.