Cell populations synthesizing cartilage proteoglycan core protein in the early chick limb bud

Cartilage specific macromolecules are known to be synthesized in the mesenchyme of the embryonic chick limb bud, especially in areas of prechondrogenic condensations (Shinomura et al, 1984). Even though the mesenchyme seems homogeneous according to histological criteria, studies in the past have suggested the presence of different cell populations with different chondrogenic potential (Solursh et al, 1982; Swalla et al, 1984). In this study we have investigated by means of flow cytometry, the synthesis of proteoglycan core protein during early development of the chick limb bud in order to identify the different chondrocyte progenitor cells. We were able to identify by virtue of different size and density a cell population which synthesizes core protein extensively at stage 24 and stage 25 of development. This cell population synthesizes core protein predominantly at the proximal half of the limb bud at stage 24. However at stage 25 the same population synthesizes core protein predominantly at the distal half of the limb bud. These observations indicate that the distal half of stage 25 limb bud is mostly homogeneous with prechondrogenic cells and is in agreement with in vitro experiments that show high chondrogenic potential of the mesenchymal cells from this stage.