Cellular stages in cartilage formation as revealed by morphometry, radioautography and type II collagen immunostaining of the mandibular condyle from weanling rats

Abstract

The role played by cell addition, cell enlargement, and matrix deposition in the endochondral growth of the condyle was assessed in weanling rats by four approaches making use of the light microscope: morphometry, 3H-thymidine radioautography, 3H-proline radioautography, and immunostaining for the cartilage-specific type II collagen. From the articular surface down, the condyle may be divided into five layers made up of cells embedded in a matrix: 1) the articular layer composed of static cells in a matrix rich in fibers presumed to be of type I collagen, 2) the polymorphic cell layer including the progenitor cells from which arise the cells undergoing endochondral changes, 3) the flattened cell layer in which cells produce a precartilagenous matrix devoid of type II collagen while undergoing differentiation in two stages: a "chondroblast" stage and a short "flattened chondrocyte" stage when intracellular type II collagen elaboration begins, 4) the upper hypertrophic cell layer, in which cells are "typical chondrocytes" that enlarge at a rapid rate, actively produce type II collagen, and deposit it into a cartilagenous matrix, and 5) the lower hypertrophic cell layer, composed of chondrocytes at a stage of terminal enlargement while the cartilagenous matrix is adapting for mineralization. 3H-thymidine radioautographic results indicate that the turnover time of progenitor cells in the polymorphic cell layer is about 2.9 days. The time spent by cells at each stage of development is estimated to be 1.4 days as chondroblasts, 0.5 days as flattened chondrocytes, 2.3 days as the chondrocytes of the upper hypertrophic cell layer, and 1.1 days as those of the lower hypertrophic cell layer. Calculations referring to a 1 x 1-mm square-sided column extending from the articular surface to the zone of vascular invasion provide the daily rate of cell addition (0.0077 mm3), extracellular matrix deposition (0.0127 mm3), and cell enlargement (0.0302 mm3). Hence the respective contribution of the three factors to condyle growth is in a ratio of about 1:1.6:4. This result emphasizes the role played by cell enlargement in the overall growth of the condyle.

Temporomandibular joint formation and condyle growth require Indian hedgehog signaling

“…This finding is likely due to the fact that PTHrP expression and cell proliferation are quite low in the polymorphic progenitor cell layer, rendering it unable to supply a sufficient number of chondroprogenitor cells and chondrocytes for condyle's appositional growth (Luder et al, 1988;Rabie and Hagg, 2002;Shibata et al, 2006). These data and interpretation suggest that the Ihh-PTHrP regulatory loop, originally suggested to operate between prehypertrophic and peri-articular chondrocytes in developing long bones Lanske et al, 1996), would normally operate equally well between Ihh-expressing condylar chondrocytes and Sox9-expressing polymorphic layer progenitor cells, pointing to its dexterity and versatility also suggested by our recent study on cranial base synchondroses (Young et al, 2006).…”

“…The condyle condensation faces the developing temporal bone, but at this early stage, there is no obvious sign of an intervening articular disc primordium. The condylar condensation differentiates into cartilage, forms a growth plate-like structure, and becomes distinguishable into four distinct portions along its main axis: a fibrous cell layer, a polymorphic progenitor cell layer, a zone of flattened chondrocytes, and a zone of hypertrophic chondrocytes (Luder et al, 1988). The so-structured condyle exhibits fairly rapid growth and elongation toward the differentiating temporal bone.…”

Lubricin is Required for the Structural Integrity and Post-natal Maintenance of TMJ

“…Wild-type condylar articular cartilage displayed characteristic features as described previously (Luder et al, 1988;Shibukawa et al, 2007;Kinumatsu et al, 2011): a superficial layer (sf) composed of 1-3 layers of flattened superficial cells; a polymorphic (pm) cell layer (Figs. 2A-2D).…”

Roles of Chondrocytes in Endochondral Bone Formation and Fracture Repair

“…This developmental difference is reflected in its superficial layer, which comprises a perichondrium with undifferentiated (prechondroblastic) cells that secrete a type I collagen-rich matrix rather than type II collagen matrix, typical of chondrocytes (Mizoguchi et al 1990;Silbermann et al 1987). Under normal functional conditions, it is these undifferentiated cells-rather than the chondrocytes in the deeper layers-that proliferate and mature to effect growth at the MCC (Luder et al 1988;Petrovic et al 1975). However, immobilization of the mandible or removal of the MCC from its normal functional environment produces a relatively rapid conversion of these prechondroblastic cells to an osteoblastic phenotype (Duterloo and Wolters 1971;Petrovic et al 1975).…”