Expression of rib-1, a caenorhabditis elegans homolog of the human tumor suppressor EXT genes, is indispensable for heparan sulfate synthesis and embryonic morphogenesis

Hiroshi Kitagawa, Tomomi Izumikawa, Souhei Mizuguchi, Katsufumi Dejima, Kazuko H. Nomura, Noriyuki Egusa, Fumiyasu Taniguchi, Jun Ichi Tamura, Keiko Gengyo-Ando, Shohei Mitani, Kazuya Nomura, Kazuyuki Sugahara

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)

Abstract

The proteins encoded by all of the five cloned human EXT family genes (EXT1, EXT2, EXTL1, EXTL2, and EXTL3), members of the hereditary multiple exostoses gene family of tumor suppressors, are glycosyltransferases required for the biosynthesis of heparan sulfate. In the Caenorhabditis elegans genome, only two genes, rib-1 and rib-2, homologous to the mammalian EXT genes have been identified. Although rib-2 encodes an N-acetylglucosaminyltransferase involved in initiating the biosynthesis and elongation of heparan sulfate, the involvement of the protein encoded by rib-1 in the biosynthesis of heparan sulfate remains unclear. Here we report that RIB-1 is indispensable for the biosynthesis and for embryonic morphogenesis. Despite little individual glycosyltransferase activity by RIB-1, the polymerization of heparan sulfate chains was demonstrated when RIB-1 was coexpressed with RIB-2 in vitro. In addition, RIB-1 and RIB-2 were demonstrated to interact by pulldown assays. To investigate the functions of RIB-1 in vivo, we depleted the expression of rib-1 by deletion mutagenesis. The null mutant worms showed reduced synthesis of heparan sulfate and embryonic lethality. Notably, the null mutant embryos showed abnormality at the gastrulation cleft formation stage or later and arrested mainly at the 1-fold stage. Nearly 100% of the embryos died before L1 stage, although the differentiation of some of the neurons and muscle cells proceeded normally. Similar phenotypes have been observed in rib-2 null mutant embryos. Thus, RIB-1 in addition to RIB-2 is indispensable for the biosynthesis of heparan sulfate in C. elegans, and the two cooperate to synthesize heparan sulfate in vivo. These findings also show that heparan sulfate is essential for post-gastrulation morphogenic movement of embryonic cells and is indispensable for ensuring the normal spatial organization of differentiated tissues and organs.

Original languageEnglish
Pages (from-to)8533-8544
Number of pages12
JournalJournal of Biological Chemistry
Volume282
Issue number11
DOIs
Publication statusPublished - 2007 Mar 16

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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