SPATIAL AND TEMPORAL CHANGES IN THE EXPRESSION OF FIBROGLYCAN (SYNDECAN-2) DURING MOUSE EMBRYONIC-DEVELOPMENT

Fibroglycan (syndecan-2) is a member of a family of cell surface hepar an sulfate proteoglycans that interact with adhesion molecules, growth factors and a variety of other effector systems that support the shap ing, maintenance and repair of an organism. To investigate this appare nt redundancy of proteoglycans at the cell surface, we have studied th e expression of fibroglycan in the mouse embryo and compared this expr ession with that of syndecan-1. The characterisation of mouse embryo c DNA clones that crosshybridized to human fibroglycan-cDNA predicted th at murine and human fibroglycan were highly similar in structure. Cons istently, the analysis of transfectant cells, murine cell lines and em bryo extracts indicated that the murine proteoglycan reacted specifica lly with monoclonal antibody 10H4 developed against the human protein. Fibroglycan, as detected by monoclonal antibody 10H4 in sections of e mbryonic tissues, occurred exclusively on mesenchymal cells that repre sented the putative precursors of the hard and connective tissue cells . No fibroglycan was detected in epithelia or in muscle cells. Areas w here fibroglycan was particularly abundant were sites of high morphoge netic activity where intense cell-cell and cell-matrix interactions ar e known to occur (e.g. the epithelial-mesenchymal interfaces, the prec hondrogenic and preosteogenic mesenchymal condensations). The expressi on of fibroglycan was weak in the early embryo, culminated during the morphogenetic phase and at the moment of cell lineage differentiation, and persisted in the perichondrium, periosteum and connective tissue cells. Syndecan-1, in contrast, was primarily detected in epithelia, a nd transiently in some mesenchymal cells, with mesenchymal localisatio ns that did not or only partially overlap with those of fibroglycan. I n situ hybridization analyses confirmed these expression patterns at t he transcriptional level, identifying mesenchymal cells as the major s ource of fibroglycan production. These data indicate that the expressi on of fibroglycan occurs along unique and developmentally regulated pa tterns, and suggest that fibroglycan and syndecan-1 may have distincti ve functions during tissue morphogenesis and differentiation.