Expression and role of c-myc in chondrocytes undergoing endochondral ossification

• Published in: The Journal of biological chemistry Vol. 268; no. 13; pp. 9645 - 9652
• Main Authors: IWAMOTO, M, YAGAMI, K, VALLE, P. L, OLSEN, B. R, PETROPOULOS, C. J, EWERT, D. L, PACIFICI, M
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Biochemistry and Molecular Biology 05.05.1993
• Subjects: Animals; Autoradiography; Base Sequence; Biological and medical sciences; Blotting, Northern; Cartilage - embryology; Cartilage - physiology; Cell differentiation, maturation, development, hematopoiesis; Cell Division - drug effects; Cell physiology; Cells, Cultured; Chick Embryo; Collagen - genetics; DNA - biosynthesis; DNA - genetics; DNA Replication; Exons; Fundamental and applied biological sciences. Psychology; Gene Expression; Genes, myc; In Situ Hybridization; Kinetics; Molecular and cellular biology; Molecular Sequence Data; Oligodeoxyribonucleotides; Oligonucleotides, Antisense - pharmacology; Osteogenesis; Promoter Regions, Genetic; RNA, Messenger - genetics; RNA, Messenger - metabolism; Sternum; Thionucleotides - pharmacology; Thymidine - metabolism; Transcription, Genetic; Tritium; Cell proliferation; Vertebrata; Chondrocyte; Collagen; Chicken; Aves; Cell differentiation; Gene expression; Ossification
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(18)98398-5

To analyze the relationship between c-myc gene expression and chondrocyte proliferation and maturation during endochondral ossification, Day 18-19 chick embryo sterna were pulse-labeled with [3H]thymidine, and serial sections were processed for autoradiography and in situ hybridization. Proliferating chondrocytes, located in four distinct areas of the developing sternum, all contained high levels of c-myc transcripts, whereas postmitotic chondrocytes (such as hypertrophic chondrocytes) contained undetectable amounts. These findings were confirmed by Northern blot analysis and by the observation that antisense c-myc oligomer treatment inhibited proliferation in cultured chondrocytes. Constitutive overexpression of c-myc by retroviral vectors in immature chondrocyte cultures (c-myc cultures) maintained the cells in a proliferative state and blocked their maturation into hypertrophic chondrocytes. The lack of maturation in the c-myc cultures was corroborated by analysis of type X collagen gene regulation. Control immature cultures contained strong repressor activity for the type X collagen gene promoter, as revealed by transfection assays; repressor activity was lost upon maturation and activation of type X collagen synthesis. In the c-myc cultures, however, repressor activity persisted. Thus, c-myc participates in the normal changes in proliferation accompanying chondrocyte maturation in vivo and in culture. The decreases in c-myc expression and cell proliferation appear to be required for completion of maturation.