Dally-like protein, a new Drosophila glypican with expression overlapping with wingless.

Proteoglycans, the molecules of extracellular matrix, carry a highly negative charge due to their glycosaminoglycan (GAG) chains and large volumes. They were considered to play a secondary role in activities like cell division, adhesion, blood coagulation, etc. until the importance of their sugar chains in the fibroblast growth factor (FGF) signalling was discovered (Science 252 (1991) 1705; Cell 64 (1991) 841). Studies of mutations in the genes sugarless(sgl) and sulfateless (sfl) have proved that the proteoglycans involved in Wg signalling contain heparan sulfate GAG chains (Development 124 (1997) 2623; Development 124 (1997) 3055; Development 124 (1997) 3565; Development 126 (1999) 3715). This has led to the attribution of specific functions to these molecules (J. Cell Biol. 148 (2000) 227). The Glypican family of heparan sulfate proteoglycans (HSPGs) is characterized by core proteins with conserved cysteine residues and attachment to the cell surface by a glycosylphosphatidyl inositol (GPI) anchor. This may lead to endocytic pathways that are different from other HSPGs, higher lateral mobility and possible apical localisation in a cell (Proc. Natl. Acad. Sci, USA 85 (1988) 9557). Variations in their HS contents may effect binding properties and localisation (J. Cell Biol. 124 (1994) 149; J. Cell Biol. 132 (1996) 487), thus specialising each member for a unique biological function. Glypicans play important roles in morphogenetic pathways, e.g. human glypican 3 (GPC3) is mutated in Simpson-Golabi-Behmel syndrome making an individual prone to tumours (Nat. Genet. 12 (1996) 241). Dally, the first Drosophila member of the family, is essential for the wingless and decapentaplegic signalling pathways (Development 121 (1995) 3687; Development 124 (1997) 4113). Here, we report a new Drosophila glypican, dally-like protein (dlp) with all the features of a glypican. Based on expression studies we report its colocalisation with Wg.