| Heparan sulfate proteoglycans (HSPGs) are molecules that are present on the cell surface or secreted extracellularly, and function in a wide variety of biological processes. HSPGs are composed of a core protein to which heparan sulfate (HS) chains, alternating glucuronic acid and N-acetyl glucosamine resides, are attached. The sugar chains undergo a series of extensive modifications beginning with N-deacetylation and N-sulfation of a subset of the glucosamine residues. Subsequently, a subset of glucuronic acid residues is converted to iduronic acid by HS C5-epimerase. Following epimerization, the chains are further modified via the O-sulfation (OST) pathway. Sulfates are added to the 2-O position of uronic acid residues and at the 6-O and 3-O positions of glucosamine residues to create unique, sulfated domains termed the HS fine structure. The HS fine structure, mediated by members of the O-sulfation pathway, confers the distinct, specific binding properties of HS.;I examined the developmental effects of disrupting the pathway that regulates specific HS "fine structure" domains in the zebrafish, Danio rerio. Initial work focused on the identification and cloning of the O-sulfation pathway. Zebrafish contain one 2-OST gene, four 6-OST genes and eight 3-OST genes, all of which show high homology to previously characterized vertebrate genes. A gene knockdown screen, using morpholinos specific to each OST, resulted in several distinct phenotypic classes, including defects in left-right development. Specific knockdown of two members of the 3-OST family, 3-OST-5 and 3-OST-6, showed a high rate of reversed heart and gut looping. Knockdown of closely related 3-OST family members had no effect on left-right development. Further phenotypic characterization of HS 3-OST-5 and -6 suggests they play distinct and important roles in the left-right pathway.;These findings, along with collaborations emerging from my work, will give the field new tools and insights into how the HS fine structure is functionally regulated in vertebrate species.;Relatively little information is known about how HS chains affect biological development in vertebrates. Studies in invertebrates, and a few in vertebrates, have begun to define the roles of HS function in vivo, but a large expansion of 6-OST and 3-OST gene families in vertebrates suggests regulation of HS fine structure is more complex in these organisms. |
