Regulation of zebrafish skeletogenesis by ext2/dackel and papst1/pinscher.

Mutations in human Exostosin genes (EXTs) confer a disease called Hereditary Multiple Exostoses (HME) that affects 1 in 50,000 among the general population. Patients with HME have a short stature and develop osteochondromas during childhood. Here we show that two zebrafish mutants, dackel (dak) and pinscher (pic), have cartilage defects that strongly resemble those seen in HME patients. We have previously determined that dak encodes zebrafish Ext2. Positional cloning of pic reveals that it encodes a sulphate transporter required for sulphation of glycans (Papst1). We show that although both dak and pic are required during cartilage morphogenesis, they are dispensable for chondrocyte and perichondral cell differentiation. They are also required for hypertrophic chondrocyte differentiation and osteoblast differentiation. Transplantation analysis indicates that dak(-/-) cells are usually rescued by neighbouring wild-type chondrocytes. In contrast, pic(-/-) chondrocytes always act autonomously and can disrupt the morphology of neighbouring wild-type cells. These findings lead to the development of a new model to explain the aetiology of HME.

Heparan sulfate Ndst1 regulates vascular smooth muscle cell proliferation, vessel size and vascular remodeling.

Heparan sulfate proteoglycans are abundant molecules in the extracellular matrix and at the cell surface. Heparan sulfate chains are composed of groups of disaccharides whose side chains are modified through a series of enzymatic reactions. Deletion of these enzymes alters heparan sulfate fine structure and leads to changes in cell proliferation and tissue development. The role of heparan sulfate modification has not been explored in the vessel wall. The goal of this study was to test the hypothesis that altering heparan sulfate fine structure would impact vascular smooth muscle cell (VSMC) proliferation, vessel structure, and remodeling in response to injury. A heparan sulfate modifying enzyme, N-deacetylase N-sulfotransferase1 (Ndst1) was deleted in smooth muscle resulting in decreased N- and 2-O sulfation of the heparan sulfate chains. Smooth muscle specific deletion of Ndst1 led to a decrease in proliferating VSMCs and the circumference of the femoral artery in neonatal and adult mice. In response to vascular injury, mice lacking Ndst1 exhibited a significant reduction in lesion formation. Taken together, these data provide new evidence that modification of heparan sulfate fine structure through deletion of Ndst1 is sufficient to decrease VSMC proliferation and alter vascular remodeling.

Axon sorting in the optic tract requires HSPG synthesis by ext2 (dackel) and extl3 (boxer).

Retinal ganglion cell (RGC) axons are topographically ordered in the optic tract according to their retinal origin. In zebrafish dackel (dak) and boxer (box) mutants, some dorsal RGC axons missort in the optic tract but innervate the tectum topographically. Molecular cloning reveals that dak and box encode ext2 and extl3, glycosyltransferases implicated in heparan sulfate (HS) biosynthesis. Both genes are required for HS synthesis, as shown by biochemical and immunohistochemical analysis, and are expressed maternally and then ubiquitously, likely playing permissive roles. Missorting in box can be rescued by overexpression of extl3. dak;box double mutants show synthetic pathfinding phenotypes that phenocopy robo2 mutants, suggesting that Robo2 function requires HS in vivo; however, tract sorting does not require Robo function, since it is normal in robo2 null mutants. This genetic evidence that heparan sulfate proteoglycan function is required for optic tract sorting provides clues to begin understanding the underlying molecular mechanisms.

Sulfatase 1 is an inhibitor of ductal morphogenesis with sexually dimorphic expression in the urogenital sinus.

The prostate gland develops from the urogenital sinus in response to circulating androgens. Androgens initiate and stimulate branching morphogenesis in the urogenital sinus via unknown mediators. Heparan sulfate proteoglycans are important extracellular molecules that sequester many growth factors in the extracellular matrix and facilitate signaling by some growth factors as part of ternary complexes that include growth factors, receptors, and heparan sulfate chains. Several enzymes modify the chemical structure of heparan sulfate to further regulate its activity. An examination of these enzymes for sexually dimorphic expression in the urogenital sinus identified Sulfatase 1 (Sulf1) as an enzyme that was down-regulated in the male urogenital sinus coincident with the initiation of prostatic morphogenesis. Down-regulation of Sulf1 was accompanied by an increase in the most highly sulfated forms of heparan sulfate, and a similar increase was observed in female urogenital sinuses treated with testosterone. Inhibiting de novo sulfation of heparan sulfate blocked prostatic morphogenesis, supporting the importance of heparan sulfate modification for prostate development. To functionally test the specific role of Sulf1 during prostate development, Sulf1 was ectopically expressed in the urogenital sinus. It partially inhibited testosterone-stimulated ductal morphogenesis, and it reduced the activation of fibroblast growth factor receptors as well as the ERK1 and ERK2 MAPKs. These data identify sulfatase 1 as an inhibitor of prostatic branching morphogenesis and growth factor signaling that is down-regulated as part of the normal response to androgen action in the male urogenital sinus.

Alterations in heparan sulfate in the vessel in response to vascular injury in the mouse.

Heparan sulfate (HS) is ubiquitous throughout the human body. The backbone of HS is composed of many types of sugars. HS serves as a docking site for a vast array of protein ligands. Recent evidence suggests a unique diversity in HS structure that alters protein binding and protein function. This diversity in HS structure has been overlooked till now. The goal of this study was to determine whether femoral artery wire injury modified HS structure. Femoral artery wire injury was performed in 16-week-old male C57BL6 mice. Transcript levels of a panel of enzymes that regulate HS fine structure, including N-deacetylase-N-sulfotransferases (Ndst) 1 and 2, exostoses (Ext) 1 and 2, C5 epimerase, and 2-O and 6-O sulfotransferases, were quantified with real-time quantitative polymerase chain reaction at 7 and 14 days post injury. All enzymes showed significant alterations in messenger RNA expression in response to injury. Ndst1, the most prevalent isoform, exhibited a 20-fold increase in response to injury. Injury induced significant alterations in fine structure specially increases in N-sulfated disaccharides at 14 days post injury. Vascular injury invokes transcriptional regulation of the enzymes that regulate HS structure, as well as changes in the pattern of HS chains in the vessel wall 14 days post injury. These findings may be important as the foundation of altered growth factor and chemokine binding in the process of vascular remodeling.

Functional conservation of the human EXT1 tumor suppressor gene and its Drosophila homolog tout velu.

Heparan sulfate proteoglycans play a vital role in signaling of various growth factors in both Drosophila and vertebrates. In Drosophila, mutations in the tout velu (ttv) gene, a homolog of the mammalian EXT1 tumor suppressor gene, leads to abrogation of glycosaminoglycan (GAG) biosynthesis. This impairs distribution and signaling activities of various morphogens such as Hedgehog (Hh), Wingless (Wg), and Decapentaplegic (Dpp). Mutations in members of the exostosin (EXT) gene family lead to hereditary multiple exostosis in humans leading to bone outgrowths and tumors. In this study, we provide genetic and biochemical evidence that the human EXT1 (hEXT1) gene is conserved through species and can functionally complement the ttv mutation in Drosophila. The hEXT1 gene was able to rescue a ttv null mutant to adulthood and restore GAG biosynthesis.

A unique role for 6-O sulfation modification in zebrafish vascular development.

Heparan sulfate proteoglycans are important modulators of growth factor signaling in a variety of patterning processes. Secreted growth factors that play critical roles in angiogenesis bind to heparan sulfate, and this association is affected by 6-O-sulfation of the heparan sulfate chains. Addition of 6-O-sulfate is catalyzed by a family of sulfotransferases (HS6STs), and genetic manipulation of their function permits an assessment of their contribution to vascular assembly. We report on the biochemical activity and expression patterns of two zebrafish HS6ST genes. In situ hybridization reveals dynamic and distinct expression patterns of these two genes during development. Structural analysis of heparan sulfate from wild-type and morpholino antisense 'knockdown' embryos suggests that HS6ST-1 and HS6ST-2 have similar biochemical activity. HS6ST-2, but not HS6ST-1, morphants exhibit abnormalities in the branching morphogenesis of the caudal vein during embryonic development of the zebrafish. Our finding that HS6ST-2 is required for the branching morphogenesis of the caudal vein is the first in vivo evidence for an essential role of a gene encoding a heparan sulfate modifying enzyme in vertebrate angiogenesis. Our analysis of two zebrafish HS6ST genes suggests that a wide range of biological processes may be regulated by an array of sulfation-modifying enzymes in the vertebrate genome.