title: Dimerized glycosaminoglycan chains increase FGF signaling during zebrafish development.
abstract: Proteoglycans (PGs) modulate numerous signaling pathways during development through binding of their glycosaminoglycan (GAG) side chains to various signaling molecules, including fibroblast growth factors (FGFs). A majority of PGs possess two or more GAG side chains, suggesting that GAG multivalency is imperative for biological functions in vivo. However, only a few studies have examined the biological significance of GAG multivalency. In this report, we utilized a library of bis- and tris-xylosides that produce two and three GAG chains on the same scaffold, respectively, thus mimicking PGs, to examine the importance of GAG valency and chain type in regulating FGF/FGFR interactions in vivo in zebrafish. A number of bis- and tris-xylosides, but not mono-xylosides, caused an elongation phenotype upon their injection into embryos. In situ hybridization showed that elongated embryos have elevated expression of the FGF target gene mkp3 but unchanged expression of reporters for other pathways, indicating that FGF/FGFR signaling was specifically hyperactivated. In support of this observation, elongation can be reversed by the tyrosine kinase inhibitor SU5402, mRNA for the FGFR antagonist sprouty4, or FGF8 morpholino. Endogenous GAGs seem to be unaffected after xyloside treatment, suggesting that this is a gain-of-function phenotype. Furthermore, expression of a multivalent but not a monovalent GAG containing syndecan-1 proteoglycan recapitulates the elongation phenotype observed with the bivalent xylosides. On the basis of these in vivo findings, we propose a new model for GAG/FGF/FGFR interactions in which dimerized GAG chains can activate FGF-mediated signal transduction pathways.
authors.affiliation: Department of Medicinal Chemistry, University of Utah, Salt Lake City, UT, USA.
authors.forename: Thao K N
authors.initials: TK
authors.lastname: Nguyen
authors.forename: Vy M
authors.initials: VM
authors.lastname: Tran
authors.forename: Venkataswamy
authors.initials: V
authors.lastname: Sorna
authors.forename: Inger
authors.initials: I
authors.lastname: Eriksson
authors.forename: Akinori
authors.initials: A
authors.lastname: Kojima
authors.forename: Mamoru
authors.initials: M
authors.lastname: Koketsu
authors.forename: Duraikkannu
authors.initials: D
authors.lastname: Loganathan
authors.forename: Lena
authors.initials: L
authors.lastname: Kjellén
authors.forename: Richard I
authors.initials: RI
authors.lastname: Dorsky
authors.forename: Chi-Bin
authors.initials: CB
authors.lastname: Chien
authors.forename: Balagurunathan
authors.initials: B
authors.lastname: Kuberan
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D019281:Dimerization; D004625:Embryo, Nonmammalian / Q000187:drug effects / Q000378:metabolism; D005346:Fibroblast Growth Factors / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D006025:Glycosaminoglycans / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D006027:Glycosides / Q000737:chemistry; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D017468:Receptors, Fibroblast Growth Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D053668:Syndecan-1 / Q000378:metabolism; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D006025:Glycosaminoglycans; D006027:Glycosides; D047428:Protein Kinase Inhibitors; D011758:Pyrroles; D017468:Receptors, Fibroblast Growth Factor; C105686:SU 5402; D053668:Syndecan-1; D029961:Zebrafish Proteins; C517774:fgf8a protein, zebrafish; C010807:xylosides; D005346:Fibroblast Growth Factors