Figure 7. Label-retaining perichondral cells are cartilage progenitors in the adult metapterygium.

(a) After a 3 day chase, EdU retention is detected in cells of the outer and (b) inner perichondrium. (c-d) After a 1 month chase, EdU-retaining cells are additionally detected inside cartilage canals. (e) After a 5.5 month chase, EdU-retaining cells are detected in abundance in the inner perichondrium, and also in peripheral chondrocytes, including (f) in the hyaline cartilage of the intertesseral joint region and (g) in hyaline cartilage beneath tesserae. (h) EdU-retaining cells are detected in greater abundance inside cartilage canals, and (i) can also be seen migrating from inside cartilage canals into adjacent ECM. (j) EdU-retaining chondrocytes are also detected in the core of the metapterygium, adjacent to the blind end of cartilage canals. For each panel, the same section was imaged for EdU detection (counterstained with DAPI), and subsequently stained with modified Masson’s trichrome. In histochemical images, EdU+ nuclei in the perichondrium or in cartilage canals are indicated with arrowheads, while EdU+ chondrocytes are indicated with an asterisk. Plane of section as indicated in Figure 1i. can, canal; pc, perichondrium; ts, tesserae. Scale bars: (a-c) 50 μm, (d) 30 μm, (e-g) 50 μm, (h-j) 30 μm.