Mouse endosialin, a C-type lectin-like cell surface receptor: expression during embryonic development and induction in experimental cancer neoangiogenesis.

Endosialin is a C-type lectin-like cell surface receptor of unknown function, with a distinctive pattern of endothelial expression in newly formed blood vessels in human cancers. The murine orthologue of endosialin has been identified, opening up the analysis of developmental regulation in the embryo and in aberrant tissue remodeling, notably cancer angiogenesis. To advance these studies we have generated an antibody to the extracellular domain of mouse endosialin and mapped protein expression from embryonic day E10.0 to the adult stage, complemented by mRNA quantification and co-typing for standard endothelial markers. Four main findings emerged. First, endosialin protein is restricted to vascular endothelium and fibroblast-like cells in developing organs, and largely disappears in the adult. Second, endothelial expression varies markedly between organs regarding spatial and temporal patterns. For instance, in the E10.0 embryo, endosialin is prominent in the endothelium of the dorsal aorta and, from E11.0 to E14.5, in vessels sprouting from the dorsal aorta, in perineural vascular plexuses, and in brain capillaries. Third, circumscribed mesenchymal expression in fibroblast-like cells was evident throughout development, most pronounced adjacent to certain budding epithelia, as exemplified by the lung and kidney glomeruli, but unrelated to the endothelial expression. The endosialin protein persists in the stromal fibroblasts of the adult uterus. Finally, in subcutaneous cancer xenograft models endosialin re-appears in the host-derived tumor stroma, both in neo-angiogenic vascular endothelium and in activated stromal fibroblasts. In future studies, the search for intrinsic or extrinsic signals contributing to endosialin induction in cancer stroma will be of interest.