Expression and role of c-myc in chondrocytes undergoing endochondral ossification.
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.
Iwamoto
M
M
Department of Anatomy-Histology, University of Pennsylvania Dental School, Philadelphia 19104-6003.
Yagami
K
K
Lu Valle
P
P
Olsen
B R
BR
Petropoulos
C J
CJ
Ewert
D L
DL
Pacifici
M
M
D000818:Animals; D001345:Autoradiography; D001483:Base Sequence; D015152:Blotting, Northern; D002356:Cartilage / Q000196:embryology / Q000502:physiology*; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D002642:Chick Embryo; D003094:Collagen / Q000235:genetics; D004247:DNA / Q000096:biosynthesis / Q000235:genetics*; D004261:DNA Replication; D005091:Exons; D015870:Gene Expression; D016259:Genes, myc; D017403:In Situ Hybridization; D007700:Kinetics; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010012:Osteogenesis; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013249:Sternum; D013873:Thionucleotides / Q000494:pharmacology; D013936:Thymidine / Q000378:metabolism; D014158:Transcription, Genetic; D014316:Tritium
D009838:Oligodeoxyribonucleotides; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D013873:Thionucleotides; D014316:Tritium; D003094:Collagen; D004247:DNA; D013936:Thymidine