Glycosaminoglycan synthesis by the apical ectodermal ridge of chick limb bud.

Abstract

The apical ectodermal ridge (AER) along the distal periphery of the embryonic chick limb bud seems to have a decisive influence on the development of subjacent mesenchymal cells, preventing cartilage differentiation but ensuring the outgrowth and formation of distal limb structures1–5. It has been suggested that when mesenchymal cells leave the AER's influence, they undergo an ultimate cell–cell interaction that triggers chondrogenic differentiation by elevating cyclic AMP levels6–8. Moreover, the AER may inhibit the differentiation of subjacent mesenchymal cells by causing them to secrete a considerable quantity of hyaluronate which by accumulating extracellularly may prevent the cell–cell interaction necessary to trigger differentiation9. Here, we have examined the synthesis of hyaluronate and other glycosaminoglycans by the AER and by limb and non-limb ectodermal tissues that do not promote limb bud outgrowth1,5,10,11. We find that there is a selective and substantial increase in the amount of hyaluronate produced by the AER compared with the non-inductive ectodermal tissues.