Journal of Histochemistry & Cytochemistry 60(12) 885 –897 © The Author(s) 2012 Reprints and permission: sagepub.com/journalsPermissions.nav

Proteoglycans are present in all members of the Bilateria and therefore have a long evolutionary history. Moreover, they are widespread components of most tissues and organs and can sometimes be a dominant component (e.g., in the vertebrate cartilage matrix). Studies of proteoglycans ini-tially focused on this tissue, since the major component, now known as aggrecan (Aspberg 2012), is abundant and readily purified. However, it is now clear that virtually all extracellular matrices contain proteoglycans, and they are also present in the pericellular matrix of many cell types. Moreover, they are not restricted to extracellular locations, since some are specialized components of membrane-bound secretory granules—for example, heparin and highly sul-fated forms of chondroitin are present in the granules of mast cells, other leukocytes, and endodermal and endothe