Figure 8. Spontaneous repair of hyaline cartilage in the skate.

(a) 3D reconstruction of a dissected metapterygium 2 weeks following experimental cartilage injury. Note the biopsy (red asterisk) has left a void of ~1/3 the diameter of the metapterygium. (b, bⁱ) By 2 months post-operation (p.o.), the injury site has been filled with a fibrous connective tissue, and (c, cⁱ) by 3 months p.o., this connective tissue begins to differentiate into cartilage. Note that the cells of the repair tissue adopt chondrocyte morphology, and the ECM of the repair tissue is integrated with adjacent cartilage. (d) By 12 months p.o., the injury site has been completely filled with repair cartilage. (dⁱ) Red staining of ECM at the surface of the repair tissue (*) could indicate the re-appearance of tissue with a perichondral-like nature, or the re-establishment of tesserae at the injured surface of the metapterygium. However, (dⁱⁱ) the vast majority of repair tissue is composed of typical hyaline cartilage. (e) Immunofluorescence reveals abundant type II collagen (Col2a1) in the ECM of repair cartilage. In (b-d), the red dashed line indicates the boundary of the biopsy, and the black dashed line indicates the extent of repair cartilage. In (e) the red dashed line indicates the boundary of the biopsy, and the white dashed line indicates the extent of repair cartilage. hc, hyaline cartilage; pc, perichondrium; ts, tesserae. Scale bars: (a) 1 cm, (b) 100 μm, (bⁱ) 30 μm, (c) 100 μm, (cⁱ) 30 μm, (d) 100 μm, (dⁱ) 50 μm, (dⁱⁱ) 50 μm, (e) 50 μm.

Figure 8—figure supplement 1. Cartilage repair in the metapterygium of the skate 8 months post-operation.

(a) Eight months after cartilage biopsy, the injury site has largely filled with repair cartilage. (b) The vast majority of repair cartilage resembles typical hyaline cartilage, though (c) we also observe some superficial red staining of the ECM (*), which could indicate the re-appearance of tissue with a perichondral-like nature, or the re-establishment of superficial tesserae at the surface of the metapterygium. In all panels, the red dashed line indicates the boundary of the biopsy, and the black dashed line indicates the extent of repair cartilage.

Figure 8—figure supplement 2. Cartilage repair in the metapterygium of the skate 11 months post-operation.

(a) Eleven months after cartilage biopsy, the injury site has completely filled with repair cartilage. (b) The repair cartilage consists largely of typical hyaline cartilage, though with some superficial red staining of the ECM, which could indicate the re-appearance of tissue with a perichondral-like nature, or the re-establishment of superficial tesserae at the surface of the metapterygium. In all panels, the red dashed line indicates the boundary of the biopsy, and the black dashed line indicates the extent of repair cartilage.

Figure 8—figure supplement 3. Cartilage repair in the metapterygium of the skate 12 months post-operation.

Twelve months after cartilage biopsy, the injury site has nearly completely filled with repair cartilage. The repair cartilage consists largely of typical hyaline cartilage, though with some superficial red staining of the ECM, which could indicate the re-appearance of tissue with a perichondral-like nature, or the re-establishment of superficial tesserae at the surface of the metapterygium. The red dashed line indicates the boundary of the biopsy, and the black dashed line indicates the extent of repair cartilage. Note that this image is from a different individual than that figure in Figure 7d.

Figure 8—figure supplement 4. Collagen composition of ECM in uninjured and repair cartilage in the skate metapterygium 8 months post-operation.

(a) Immunodetection of type II collagen reveals localization to the pericellular ECM of both uninjured and repair cartilage in the metapterygium. Conversely, we detected no type I collagen in the ECM of uninjured or repair cartilage, despite (b) positive immunodetection of type I collagen in the ECM of adjacent skeletal muscle fibres. In (a) red dashed line indicates the boundary of the biopsy, with repair cartilage to the left.

Figure 8—figure supplement 5. Ectopic cartilage following perichondral disruption in the metapterygium of the skate.

(a–b) In two animals, failed biopsies resulted in damage to the perichondrium without removal of cartilage. In both instances, this resulted in the induction of large masses of ectopic cartilage beneath the perichondrium, and above the tesserae. hc, hyaline cartilage; pc, perichondrium; ts, tesserae.