TheCaenorhabditis elegansvulval morphogenesis genesqv-4encodes a UDP-glucose dehydrogenase that is temporally and spatially regulated

Abstract

The development of the Caenorhabditis elegans vulva requires the involution of epithelial cells and provides a model for organ morphogenesis. Mutations in C. elegans sqv (squashed vulva) genes affect both vulval morphogenesis and embryonic development. We found that sqv-4 encodes a protein similar to UDPglucose dehydrogenases and showed that the SQV-4 protein specifically catalyzes the conversion of UDP-glucose to UDP-glucuronic acid, which is essential for the biosynthesis of chondroitin and heparan sulfate proteoglycans. SQV-4 is expressed in the vulva and in oocytes, among many other cells, and SQV-4 levels are dramatically increased in a specific subset of vulval cells during vulval morphogenesis. We propose that the regulation of UDP-glucuronic acid production in a specific subset of vulval cells helps determine the shape of the vulva.T he significance of glycosaminoglycans (GAGs) in animal development has become evident in the past few years from studies of mutants defective in GAG biosynthesis. For example, the genes sqv-1, -3, -7, and -8 (squashed vulva) of Caenorhabditis elegans have been implicated in the biosynthesis of GAGs, based on amino acid sequence similarity between their protein products and known GAG biosynthesis enzymes and on biochemical assays (1-4). In the accompanying paper (4), we show that SQV-1 is a UDP-glucuronic acid decarboxylase and synthesizes UDP-xylose from UDP-glucuronic acid. SQV-7 translocates UDP-glucuronic acid, UDP-galactose, and UDP-N-acetylgalactosamine from the cytoplasm to the lumen of the Golgi apparatus (1, 3). SQV-3 and SQV-8 are glycosyltransferases that likely act in the lumen of the Golgi apparatus and use UDPgalactose and UDP-glucuronic acid to build the protein core-GAG-linker region of proteoglycans (1, 2, 5).Mutations in the human GAG galactosyltransferase I, the human sqv-3 ortholog, are implicated as the cause of a progeroid variant of the connective-tissue disorder Ehlers-Danlos syndrome (6, 7), a group of heritable disorders characterized by hyperelasticity of the skin and hypermobile joints. Mutations in the human EXT family of genes, which encode heparan sulfate polymerases that act in heparan sulfate GAG biosynthesis, are associated with hereditary multiple exostoses, a genetic disorder characterized by many cartilaginous outgrowths (reviewed in ref. 8).Mutations in the mammalian EXT gene family and GAG galactosyltransferase I, as well as mutations in the C. elegans sqv-1, -3, -7, and -8 genes, are all expected to cause defects in the formation or modification of chondroitin and͞or heparan sulfate GAGs. Chondroitin and heparan sulfate share the structure: (serine residue in the protein core)-xylose-galactose-galactoseglucuronic acid-(X-glucuronic acid) n , where X is N-acetylgalactosamine in chondroitin and is N-acetylglucosamine in heparan sulfate. The four sugar chain xylose-galactose-galactoseglucuronic acid is referred to as the protein core-GAG linker region and is essential for the biosynthesis of GAGs (reviewed in ref. 9).Mutations in the eight...

UDP-glucose Dehydrogenase Activity and Optimal Downstream Cellular Function Require Dynamic Reorganization at the Dimer-Dimer Subunit Interfaces

“…UGDH targeted disruption and loss of function polymorphisms that interfere with the enzyme quaternary structure and cellular stability have been implicated in cardiac malformation in multiple organisms (4,5,33,34). Moreover, the androgenstimulated expression of UGDH is important for prostate epithelial androgen solubilization and elimination.…”

The Caenorhabditis elegans Genes sqv-2and sqv-6, Which Are Required for Vulval Morphogenesis, Encode Glycosaminoglycan Galactosyltransferase II and Xylosyltransferase

“…SQV-4 converts UDP-glucose to UDP-GlcA (13). SQV-7 transports UDP-GlcA, UDP-Gal, and UDP-GalNAc from the cytoplasm to lumen of the Golgi apparatus (14).…”

“…The (12), UDP-glucose dehydrogenase (13), UDP-GlcA/UDP-Gal/ UDP-GalNAc transporter (14), and glucuronosyltransferase I (12), respectively. sqv-3 was used to identify the human galactosyltransferase I, which has been implicated in the progeroid variant of EDS (7,15).…”

The LIN-15A and LIN-56 Transcriptional Regulators Interact to Negatively Regulate EGF/Ras Signaling inCaenorhabditis elegansVulval Cell-Fate Determination

“…We used lamin as a marker for nuclear fractions (Liu et al 2000;Gruenbaum et al 2002) and SQV-4 as a marker for cytosolic material (Hwang and Horvitz 2002). The majority of the LIN-56 protein cofractionated with nuclear lamin; LIN-56 protein was barely detectable in the SQV-4-containing cytosolic fraction (see Figure 3B).…”

“…Rabbit polyclonal antiserum 3930 generated against C. elegans lamin (Gruenbaum et al 2002) was used at 1:5000 on immunoblots as a control for nuclear fractionation quality. Anti-SQV-4 antibodies (Hwang and Horvitz 2002) were used at 1:3000 on immunoblots as a control for cytosolic fractionation quality.…”