Figure 6.

Aberrant fiber structure and organization in Col5a1^Δten/Δten tendons during early tendon development. A and B: Postnatal day 4 control (Ctrl) mouse flexor digitorum longus (FDL) contained organized fibers (F) that are relatively uniform in size. The fibers were present in microdomains that were defined by tenocyte cytoplasmic processes (curved arrows). B and D: Collagen protofibrils can be seen during deposition (arrowhead). C and D:Col5a1^Δten/Δten mouse FDLs have less-organized fibers (F). In Col5a1^Δten/Δten FDLs, there are fewer fibers than in the wild-type controls. The collagen V–null FDLs have larger fibers with more heterogeneity in size than in control tendons. In addition, in the absence of collagen V, the fibers are less organized, ie, less regularly packed, with more space separating them than in the controls. In addition, the tenocyte processes (curved arrows) defining the microdomains are less organized than in the controls.