Chromatin profiling identifies chondrocyte-specific Sox9 enhancers important for skeletal development

Area of Science:

• Molecular Biology
• Developmental Biology
• Genetics

Background:

• The transcription factor SRY-related HMG box 9 (Sox9) is vital for chondrogenesis and skeletal development.
• Mutations in the SOX9 gene are linked to campomelic dysplasia (CD), a severe skeletal malformation disorder.
• Regulatory mechanisms controlling Sox9 expression in chondrocytes are not fully understood.

Purpose of the Study:

• To identify and characterize regulatory elements controlling Sox9 expression in chondrocytes.
• To investigate the role of identified enhancers in chondrogenesis and skeletal development.
• To elucidate the molecular mechanisms underlying Sox9 gene regulation in the context of skeletal disorders.

Main Methods:

• Genome-wide profiling to identify potential Sox9 enhancers.
• In vitro enhancer activity assays to assess synergistic effects.
• In vivo mouse models with targeted deletion of Sox9 enhancers (E308 and E160).
• Analysis of Sox9 expression, chondrocyte differentiation, and skeletal phenotypes in knockout mice.

Main Results:

• Two novel Sox9 enhancers, E308 (308 kb 5' upstream) and E160 (160 kb 5' upstream), were identified.
• Both enhancers demonstrated synergistic activity in regulating Sox9 expression.
• Simultaneous deletion of E308 and E160 in mice resulted in dwarfism, reduced Sox9 expression in chondrocytes, and impaired chondrogenesis.
• An upstream open chromatin region showed reorganization in deletion mice, suggesting a compensatory mechanism.

Conclusions:

• The identified enhancers E308 and E160 play a critical synergistic role in Sox9 regulation during chondrogenesis.
• Disruption of these enhancers leads to skeletal abnormalities, highlighting their importance in skeletal development.
• These findings provide insights into the molecular mechanisms of Sox9 gene regulation and the pathophysiology of skeletal disorders like campomelic dysplasia.