Daisuke Murata

Ceramide glucosyltransferase of the nematode Caenorhabditis elegans is involved in oocyte formation and in early embryonic cell division

Ceramide glucosyltransferase (Ugcg) [uridine diphosphate (UDP)-glucose:N-acylsphingosine D-glucosyltransferase or UDP-glucose ceramide glucosyltransferase (GlcT): EC 2.4.1.80] catalyzes formation of glucosylceramide (GlcCer) from ceramide and UDP-glucose. There is only one Ugcg gene in the mouse genome, which is essential in embryogenesis and brain development. The nematode Caenorhabditis elegans has three Ugcg genes (cgt-1, cgt-2 and cgt-3), and double RNAi of the cgt-1 and cgt-3 genes results in lethality at the L1 larval stage. In this study, we isolated knockout worms for the three genes and characterized the gene functions. Each gene product showed active enzymatic activity when expressed in GM95 cells deficient in glycosphingolipids (GSLs). When each gene function was disrupted, the brood size of the animal markedly decreased, and abnormal oocytes and multinucleated embryos were formed. The CGT-3 protein had the highest Ugcg activity, and knockout of its gene resulted in the severest phenotype. When cgt-3 RNAi was performed on rrf-1 worms lacking somatic RNAi machinery but with intact germline RNAi machinery, a number of abnormal oocytes and multinucleated eggs were observed, although the somatic phenotype, i.e., L1 lethal effects of cgt-1/cgt-3 RNAi, was completely suppressed. Cell surface expression of GSLs and sphingomyelin, which are important components of membrane domains, was affected in the RNAi-treated embryos. In the embryos, an abnormality in cytokinesis was also observed. From these results, we concluded that the Ugcg gene is indispensable in the germline and that an ample supply of GlcCer is needed for oocytes and fertilized eggs to maintain normal membranes and to proceed through the normal cell cycle.

Two Golgi-resident 3′-Phosphoadenosine 5′-Phosphosulfate Transporters Play Distinct Roles in Heparan Sulfate Modifications and Embryonic and Larval Development in Caenorhabditis elegans

Synthesis of extracellular sulfated molecules requires active 3′-phosphoadenosine 5′-phosphosulfate (PAPS). For sulfation to occur, PAPS must pass through the Golgi membrane, which is facilitated by Golgi-resident PAPS transporters. Caenorhabditis elegans PAPS transporters are encoded by two genes, pst-1 and pst-2. Using the yeast heterologous expression system, we characterized PST-1 and PST-2 as PAPS transporters. We created deletion mutants to study the importance of PAPS transporter activity. The pst-1 deletion mutant exhibited defects in cuticle formation, post-embryonic seam cell development, vulval morphogenesis, cell migration, and embryogenesis. The pst-2 mutant exhibited a wild-type phenotype. The defects observed in the pst-1 mutant could be rescued by transgenic expression of pst-1 and hPAPST1 but not pst-2 or hPAPST2. Moreover, the phenotype of a pst-1;pst-2 double mutant were similar to those of the pst-1 single mutant, except that larval cuticle formation was more severely defected. Disaccharide analysis revealed that heparan sulfate from these mutants was undersulfated. Gene expression reporter analysis revealed that these PAPS transporters exhibited different tissue distributions and subcellular localizations. These data suggest that pst-1 and pst-2 play different physiological roles in heparan sulfate modification and development.

GPI-anchor synthesis is indispensable for the germline development of the nematode Caenorhabditis elegans

Twenty-four Caenorhabditis elegans genes are involved in GPI-anchor synthesis. Based on the isolation of a deletion allele of the PIGA gene mediating the first step of GPI-anchor synthesis, GPI-anchor synthesis in somatic gonads and/or in germline is shown to be indispensable for the normal development of oocytes and eggs.

The ortholog of human solute carrier family 35 member B1 (UDP-galactose transporter-related protein 1) is involved in maintenance of ER homeostasis and essential for larval development in Caenorhabditis elegans

Although the solute carrier 35B1 (SLC35B1) is evolutionarily conserved, its functions in metazoans remain unknown. To elucidate its function, we examined developmental roles of an SLC35B1 family gene (HUT‐1: homolog of UDP‐Gal transporter) in Caenorhabditis elegans. We isolated a deletion mutant of the gene and characterized phenotypes of the mutant and hut‐1 RNAitreated worms. GFP‐HUT‐1 reporter analysis was performed to examine gene expression patterns. We also tested whether several nucleotide sugar transporters can compensate for hut‐1 deficiency. The hut‐1 deletion mutant and RNAi worms showed larval growth defect and lethality with disrupted intestinal morphology. Inactivation of hut‐1 induced chronic endoplasmic reticulum (ER) stress, and hut‐1 showed genetic interactions with the atf‐6, pek‐1, and ire‐1 genes involved in unfolded protein response signaling. ER ultrastructure and ER marker distribution in hut‐1‐deficient animals showed that HUT‐1 is required for maintenance of ER structure. Reporter analysis revealed that HUT‐1 is an ER protein ubiquitously expressed in tissues, including the intestine. Lethality and the ER stress phenotype of the mutant were rescued with the human hut‐1 ortholog UGTrel1. These results indicate important roles for hut‐1 in development and maintenance of ER homeostasis in C. elegans.—Dejima, K.,Murata, D., Mizuguchi, S., Nomura, K. H., Gengyo‐Ando, K.,Mitani, S., Kamiyama, S., Nishihara, S., Nomura, K. The ortholog of human solute carrier family 35 member B1 (UDP‐galactose transporter‐related protein 1) is involved in maintenance of ER homeostasis and essential for larval development in Caenorhabditis elegans. FASEBJ. 23, 2215–2225 (2009)

Chondroitin 4-O-sulfotransferase is indispensable for sulfation of chondroitin and plays an important role in maintaining normal life span and oxidative stress responses in nematodes

Chondroitin sulfate (CS)/chondroitin (Chn) chains are indispensable for embryonic cell division and cytokinesis in the early developmental stages in Caenorhabditis elegans and mice, whereas heparan sulfate (HS) is essential for axon guidance during nervous system development. These data indicate that the fundamental functions of CS and HS are conserved from worms to mammals and that the function of CS/Chn differs from that of HS. Although previous studies have shown that C. elegans produces HS and non-sulfated Chn, whether the organism produces CS remains unclear. Here, we demonstrate that C. elegans produces a small amount of 4-O-sulfated Chn and report the identification of C41C4.1, an orthologue of the human chondroitin 4-O-sulfotransferase gene. Loss of C41C4.1 in C. elegans resulted in a decline in 4-O-sulfation of CS and an increase in the number of sulfated units in HS. C41C4.1 deletion mutants exhibited reduced survival rates after synchronization with sodium hypochlorite. Collectively, these results show for the first time that CS glycans are present in C. elegans and that the Chn 4-O-sulfotransferase responsible for the sulfation plays an important role in protecting nematodes from oxidative stress.

RNAi screening of human glycogene orthologs in the nematode Caenorhabditis elegans and the construction of the C. elegans glycogene database.

In this study, we selected 181 nematode glycogenes that are orthologous to human glycogenes and examined their RNAi phenotypes. The results are deposited in the Caenorhabditis elegans Glycogene Database (CGGDB) at AIST, Tsukuba, Japan. The most prominent RNAi phenotypes observed are disruptions of cell cycle progression in germline mitosis/meiosis and in early embryonic cell mitosis. Along with the previously reported roles of chondroitin proteoglycans, glycosphingolipids and GPI-anchored proteins in cell cycle progression, we show for the first time that the inhibition of the functions of N-glycan synthesis genes (cytoplasmic alg genes) resulted in abnormal germline formation, ER stress and small body size phenotypes. The results provide additional information on the roles of glycoconjugates in the cell cycle progression mechanisms of germline and embryonic cells.

NRFL-1, the C. elegans NHERF Orthologue, Interacts with Amino Acid Transporter 6 (AAT-6) for Age-Dependent Maintenance of AAT-6 on the Membrane

The NHERF (Na+/H+ exchanger regulatory factor) family has been proposed to play a key role in regulating transmembrane protein localization and retention at the plasma membrane. Due to the high homology between the family members, potential functional compensations have been a concern in sorting out the function of individual NHERF numbers. Here, we studied C. elegans NRFL-1 (C01F6.6) (nherf-like protein 1), the sole C. elegans orthologue of the NHERF family, which makes worm a model with low genetic redundancy of NHERF homologues. Integrating bioinformatic knowledge of C. elegans proteins into yeast two-hybrid scheme, we identified NRFL-1 as an interactor of AAT-6, a member of the C. elegans AAT (amino acid transporter) family. A combination of GST pull-down assay, localization study, and co-immunoprecipitation confirmed the binding and characterized the PDZ interaction. AAT-6 localizes to the luminal membrane even in the absence of NRFL-1 when the worm is up to four-day old. A fluorescence recovery after photobleaching (FRAP) analysis suggested that NRFL-1 immobilizes AAT-6 at the luminal membrane. When the nrfl-1 deficient worm is six-day or older, in contrast, the membranous localization of AAT-6 is not observed, whereas AAT-6 tightly localizes to the membrane in worms with NRFL-1. Sorting out the in vivo functions of the C. elegans NHERF protein, we found that NRFL-1, a PDZ-interactor of AAT-6, is responsible for the immobilization and the age-dependent maintenance of AAT-6 on the intestinal luminal membrane.

Functional Glycomics at the Level of Single Cells: Studying Roles of Sugars in Cell Division, Differentiation, and Morphogenesis with 4D Microscopy

The nematode Caenorhabditis elegans is the first multicellular organism whose complete cell lineage, cellular anatomy, and neural wiring diagram of its nervous system are determined. Because the complete DNA sequence of its genome is also available, it is easy to isolate deletion mutants from TMP (trimethylpsoralen)/UV mutagenized library of animals by PCR screening with carefully designed primer sets (cf. http://shigen.lab.nig.ac.jp/c.elegans/ChangeLocale.do?lang=en&url=home). Mutant strains can be stored frozen indefinitely, and this makes this model organism the only multicellular organism compatible with high throughput biologic study. In addition, genes defined by sequence similarity to any known genes can be easily identified and mutated, and the phenotypes of mutant animals can be studied at the level of single cells as the body of the nematode is transparent.