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(TF,AY) S U M M A R Y Tooth eruption is a multifactorial process involving movement of existing tissues and formation of new tissues coordinated by a complex set of genetic events. We have used the model of the unopposed rodent molar to study morphological and genetic mechanisms involved in axial movement of teeth. Following extraction of opposing upper molars, lower molars supererupted by 0.13 mm. Labeled tissue sections revealed significant amounts of new bone and cementum apposition at the root apex of the unopposed side following supereruption for 12 days. Newly apposited cementum and alveolar bone layers were approximately 3-fold thicker in the experimental vs the control group, whereas periodontal ligament width was maintained. Tartrate-resistant acid phosphatase staining indicated bone resorption at the mesial alveolar walls of unopposed molars and provided in tandem with new bone formation at the distal alveolar walls an explanation for the distal drift of molars in this model. Microarray analysis and semiquantitative RT-PCR demonstrated a significant increase in collagen I, integrin b5, and SPARC gene expression as revealed by comparison between the unopposed molar group and the control group. Immunohistochemical verification revealed increased levels of integrin b5 and SPARC labeling in the periodontal ligament of the unopposed molar. Together our findings suggest that posteruptive axial movement of teeth was accomplished by significant formation of new root cementum and alveolar bone at the root apex in tandem with upregulation of collagen I, integrin b5, and SPARC gene expression. (J Histochem Cytochem 55:127-140, 2007)

The in vitro phenotype of bovine articular chondrocytes is described . Chondrocytes plated at high density in roller-bottle and dish cultures were maintained in vitro . The major matrix macromolecules, collagen and proteoglycan, synthesized by these cells were characterized during the course of the culture period . The chondrocytes synthesized mainly Type II Collagen, which was found predominantly in the cell-associated matrix . The media contained a mixture of Type II and Type III collagens . Type I collagen was detectable in neither the medium nor the cell-associated matrix . The proteoglycan monomers found in media and cellassociated matrix had the same hydrodynamic sizes as monomers synthesized by cartilage slices or those extracted from adult articular cartilage . The majority of proteoglycans synthesized by the cells were found in high molecular weight aggregates which were readily recovered from the media and were extractable from cell-associated matrix with low ionic strength buffers . The results demonstrate the long-term in vitro phenotypic stability of the bovine articular chondrocytes . The advantages of the in vitro system as a model for studying the effects of external agents, such as drugs and vitamins, are discussed .The major collagen type present in hyaline cartilage and a variety of chondrocyte cultures is Type II collagen (3,4,9,10,20) . The production of Type II collagen by mesenchymal cells in culture is generally taken as evidence of expression of the "chondrocytic" phenotype (17). It is thought that phenotypically stable chondrocyte cultures synthesize a small proportion of Type V (AB) collagen (4) and that this collagen type is usually present in hyaline cartilage in a pericellular location (10). This view has been challenged recently by others (1) who view the Type V collagen as a perichondrial contamination. The la, 2a, and 3a chains which have been isolated from human and bovine hyaline cartilage migrate on polyacrylamide gels in a manner similar to Type V collagen alpha chains, but they have been shown to be genetically distinct gene products (1, 6). The production of Type I collagen by so called "chondrocytic" cells has been taken as an indication of loss of phenotypic stability and as an indicator of "de-differentiation" in vitro (2,4,29) . The loss of phenotypic stability has been associated with a variety of culture conditions, especially in-THE JOURNAL OF CELL BIOLOGY " VOLUME 93 JUNE 1982 751-757 © The Rockefeller University Press -0021-9525/82/06/0751/07 $1 .00 creasing age in culture, low plating density, and passage of cells (3,4,9,22,29) . Thus, careful analysis of collagen type in chondrocyte cultures has become an essential step in establishing whether such cultures express a true cartilagenous phenotype.Proteoglycans are responsible for many of the physicochemical properties of hyaline cartilage . Proteoglycan monomers consist of a core protein to which are covalently attached glycosaminoglycans (chondroitin sulfate and keratan sulfate) and two types of oligosac...

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