Structural features of incremental line-like striations in mandibular condylar cartilage of c-src-deficient mice

Mandibular condylar cartilage is sensitive to masticatory force, while mice lacking the c-src gene (c-src-deficient mice) have osteopetrosis and tooth eruption failure. The purpose of this study was to investigate the morphology of the mandibular condyle in these mice, which were maintained with a soft-food diet for 240 days after birth. The condylar head in the c-src-deficient mice showed slight deformity in shape before weaning, but showed remarkable undergrowth after weaning. No significant morphological or histological differences were detected between the mandibular condyle in wild-type mice fed soft food and those fed hard food, indicating that osteopetrosis, as well as abnormal masticatory force, influences the morphology of the mouse mandibular condyle, and that malocclusion rather than dietary consistency may have greater influence. After 70 days, incremental line-like striations consisting of cartilaginous and non-cartilaginous layers were detected in the mandibular condyle of the c-src-deficient mice, but not in the tibial growth plate. Immunostaining of aggrecan, collagen types II and X, and osteopontin was detected in the cartilaginous layers, but not in the non-cartilaginous layers showing collagen type I immunostaining. Chondrocyte lacunae were not eroded in the cartilaginous layers, and complete circumferential mineralisation around the lacunae and impaired osteoclast (chondroclast) function can account for this phenomenon. However, repeated cessation of chondrocyte differentiation may be required to completely explain the formation of the striations. These results indicate that the mandibular condyle in the c-src-deficient mice has unique structural features, adding to its deformity.