MOLECULAR HETEROGENEITY OF CHONDROITIN SULFATE IN THE EARLY DEVELOPING CHICK WING BUD

Protcoglycans arc ubiquitous extracellular matrix molecules whose role in development remains poorly understood. In the developing chick lim b, the nature and possible roles of a number of extracellular matrix p roteins is well documented. Much less is known of the biochemical natu re, and more importantly, the roles of proteoglycans. Using a panel of monoclonal antibodies (Mabs) which recognise specific epitopes on the constituent chondroitin/dermatan sulphate chains, we show that distin ct sub-populations of proteoglycans are dynamically expressed within t he limb ectoderm, the ectodermal basement membrane and the limb mesenc hyme. In particular, prior to chondrogensis, chondroitin-6-sulphate-ri ch proteoglycans containing over-sulphated domains reside predominantl y within the mesenchymal extracellular matrix ECM, whilst chondroitin- 4-sulphate (C-4-S) is associated with the ectodermal basement membrane and subjacent mesenchymal ECM. At stage 24, C-4-S is also localized i n the prechondrogenic condensation. Concomitantly with overt chondroge nesis, the epitopes recognized by the Mabs become restricted to the ch ondrifying skeletal elements and the undifferentiated distal mesenchym e. The significance of these findings has yet to be elucidated.