Embryonic Limb Mesenchyme Micromass Culture as an In Vitro Model for Chondrogenesis and Cartilage Ma

In vitro techniques for the study of chondrogenic differentiation of embryonic limb mesenchymal cells have been available for some time. Early methods require highdensity confluent monolayer cell cultures (1 ,2 ). The micromass culture method developed by Ahrens et al. (3 ) represented a convenient system for the observations and analysis of the differentiative processes and phenomena analogous to those exhibited by the limb cartilage anlagen in situ . In these cultures, limb mesenchymal cells first undergo condensation giving rise to aggregates that later become cartilage nodules (3 ,4 ), thereby mimicking the differentiative phenomena occurring during embryonic limb development in vivo, i.e., mesenchymal condensation preceding cartilage differentiation (5 –9 ). The micromass limb mesenchymal culture system has gained great popularity for the analysis of the regulatory steps and differentiative processes that result in the condensation of the mesenchyme and the formation and maturation of the cartilage anlagen.