SOX9 and the many facets of its regulation in the chondrocyte lineage

ABSTRACT

SOX9 is a pivotal transcription factor in developing and adult cartilage. Its gene is expressed from the multipotent skeletal progenitor stage and is active throughout chondrocyte differentiation. While it is repressed in hypertrophic chondrocytes in cartilage growth plates, it remains expressed throughout life in permanent chondrocytes of healthy articular cartilage. SOX9 is required for chondrogenesis: it secures chondrocyte lineage commitment, promotes cell survival, and transcriptionally activates the genes for many cartilage-specific structural components and regulatory factors. Since heterozygous mutations within and around SOX9 were shown to cause the severe skeletal malformation syndrome called campomelic dysplasia, researchers around the world have worked assiduously to decipher the many facets of SOX9 actions and regulation in chondrogenesis. The more we learn, the more we realize the complexity of the molecular networks in which SOX9 fulfills its functions and is regulated at the levels of its gene, RNA, and protein, and the more we measure the many gaps remaining in knowledge. At the same time, new technologies keep giving us more means to push further the frontiers of knowledge. Research efforts must be pursued to fill these gaps and to better understand and treat many types of cartilage diseases in which SOX9 has or could have a critical role. These diseases include chondrodysplasias and cartilage degeneration diseases, namely osteoarthritis, a prevalent and still incurable joint disease. We here review the current state of knowledge of SOX9 actions and regulation in the chondrocyte lineage, and propose new directions for future fundamental and translational research projects.

KEYWORDS:

• Cartilage
• chondrocyte
• posttranscriptional regulation
• posttranslational modification
• SOX9
• transcriptional regulation

Funding

This review was supported by research grants from the USA/Israel Binational Science Foundation (BSF grant no. 2013145) to both authors, the National Institutes of Health to Véronique Lefebvre (AR46249 and AR60016), the European Commission Framework 7 programme (EU FP7; HEALTH.2012.2.4.5-2, DBOARD project 305815), and The Marie Curie European IRG reintegration grant (proposal 268214) to Mona Dvir-Ginzberg.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.

Additional information

Funding

This review was supported by research grants from the USA/Israel Binational Science Foundation (BSF grant no. 2013145) to both authors, the National Institutes of Health to Véronique Lefebvre (AR46249 and AR60016), the European Commission Framework 7 programme (EU FP7; HEALTH.2012.2.4.5-2, DBOARD project 305815), and The Marie Curie European IRG reintegration grant (proposal 268214) to Mona Dvir-Ginzberg.