Extracellular matrix environment influences chondrogenic pattern formation in limb bud micromass culture: Experimental verification of theoretical models

Various theoretical models have been proposed to explain the periodicity in the pattern of limb chondrogenesis, but experimental comparison of these models have seldom been performed properly. In the present study, micromass culture of limb bud mesenchyme cells was undertaken to test the validity of three theoretical models: the reaction-diffusion model, the cell sorting model, and the mechanochemical model. Computer simulations were undertaken to predict the factors that can affect the coarseness of the chondrogenic pattern. According to the predictions, we performed micromass culture of limb mesenchyme in collagen and agarose gel. Then we carried out time- lapse observation to analyze the cell movement during pattern formation. From computer simulations it was theoretically predicted that changes in the surrounding extracellular matrix should alter the periodicity of the chondrogenic pattern in vitro, and we found that pattern changes actually occurred under different culture conditions. When compared with the culture in a liquid medium, the chondrogenic pattern became less coarse when the cells were cultured in collagen or agarose gel, and the pattern change appeared to be independent of the cell differentiation. Time-lapse observation revealed a decrease in cell motility when the cells were cultured in gel. It was found that both the reaction-diffusion and cell sorting models fit the pattern change produced and that the mechanochemical model is not primarily important in the chondrogenic pattern formation in vitro.