Cell sorting and chondrogenic aggregate formation in micromass culture

Area of Science:

• Developmental Biology
• Cell Biology
• Biochemistry

Background:

• Cartilage differentiation in developing limbs involves prechondrogenic cell condensation.
• Micromass cultures of limb bud mesenchyme mimic this process, forming aggregates that can differentiate into cartilage nodules.

Purpose of the Study:

• To investigate the mechanism of aggregate formation in micromass cultures.
• To determine if cell sorting occurs during in vitro aggregate formation.
• To explore factors influencing chondrogenesis in mesenchymal cell aggregates.

Main Methods:

• Utilized chimeric mixtures of potentially chondrogenic and nonchondrogenic cell types in micromass cultures.
• Studied mixtures of distal and proximal limb mesenchyme cells.
• Examined mixtures of distal limb cells with avian tendon fibroblasts.

Main Results:

• Aggregate formation in vitro is a result of cell sorting, involving prechondrogenic cells from different limb regions.
• This contrasts with in vivo condensation, where cell sorting is not observed.
• Cell surface differences exist in undifferentiated limb mesenchyme.
• Mesenchymal cell aggregates require a threshold size for chondrogenesis to initiate.
• Nonchondrogenic cells can form aggregates under certain culture conditions.

Conclusions:

• In vitro aggregate formation in limb bud mesenchyme cultures involves cell sorting, indicating cell surface heterogeneity.
• A minimum aggregate size is necessary for chondrogenesis to proceed.
• The process of in vitro aggregate formation differs from in vivo condensation regarding cell sorting.