Division abnormally delayed (Dally) is one of two glycosylphosphatidylinositol (GPI)-linked heparan sulfate proteoglycans in Drosophila. Numerous studies have shown that it influences Decapentaplegic (Dpp) and Wingless signaling. It has been generally assumed that Dally affects signaling by directly interacting with these growth factors, primarily through its heparan sulfate (HS) chains. To understand the functional contributions of HS chains and protein core we have (1) assessed the growth factor binding properties of purified Dally using surface plasmon resonance, (2) generated a form of Dally that is not HS modified and evaluated its signaling capacity in vivo. Purified Dally binds directly to FGF2, FGF10, and the functional Dpp homolog BMP4. FGF binding is abolished by preincubation with HS, but BMP4 association is partially HS-resistant, suggesting the Dally protein core contributes to binding. Cell binding and co-immunoprecipitation studies suggest that non-HS-modified Dally retains some ability to bind Dpp or BMP4. Expression of HS-deficient Dally in vivo showed it does not promote signaling as well as wild-type Dally, yet it can rescue several dally mutant phenotypes. These data reveal that heparan sulfate modification of Dally is not required for all in vivo activities and that significant functional capacity resides in the protein core.
Bibliographical noteFunding Information:
We are grateful to P. ten Dijke, H. Nakato, the Developmental Studies Hybridoma Bank and the Bloomington Stock Center for fly stocks and reagents, and to B. Dimitroff, R. Peterson and T. Metzger for their assistance with the experiments. We especially thank T. Akiyama and H. Nakato for providing the Myc-tagged Dally and Dally ΔGAG , for the analysis of their relative expression levels and for helpful discussions. We also thank T. Akiyama and M. Serpe for their advice on binding assays, and H. Nakato and members of the Selleck laboratory for the discussions and comments on the manuscript. This work was supported by the National Institutes of Health (GM54832-09).
- Heparan sulfate