Genetic analysis of the signaling pathways that govern patterning during development in the fruitflyDrosophila melanogaster and in the nematode C. elegans have provided insight into the in vivo functions of proteoglycans and their associated glycosaminoglycans. These studies have shown that patterning events dictated by Fibroblast Growth Factor Receptors, Wnt, Transforming Growth Factor- β(TGF- β), and Hedgehog families of growth factors are regulated by proteoglycans. Recent biochemical and structural analyses have shown that the molecular machinery of glycosaminoglycan biosynthesis is highly conserved between these invertebrate organisms and mammals. Drosophila andC. elegans therefore provide powerful model systems for exploring the varied functions proteoglycans and their glycosaminoglycan modifications.