[Chondrogenesis in mouse limb bud in vitro. I. Effect of the ectoderm].

The role of the ectoderm in the chondrogenesis of mouse limb bud mesoderm was investigated in vitro at several developmental stages by analysis of the evolution of DNA content, the accumulation of sulfated glycosaminoglycans and histochemical procedures. Young limb buds or the undifferentiated apex of older buds (stages 17 and 19 of Theiler's table) from which the ectoderm had been removed with trypsin treatment initiated a large chondrogenesis but not morphogenesis. When the ectoderm was present, these limb buds showed a polarized proximal to distal outgrowth and differentiated skeletal primordia. Mesodermal cells of stage 20 limb bud apex were able to differentiate autopodial skeletons with or without the presence of the ectoderm: cartilaginous areas of the limb skeleton seem determined at this developmental stage. These results, which show the importance of the ectoderm in limb bud morphogenesis, are compared with results obtained using other methods with mouse or bird buds.