Chlorurus rhakoura Randall & Anderson, 1997 (Perciformes, Scaridae), an Indo-Pacific fish new for the Mediterranean Sea

The scarid fish Chlorurus rhakoura Randall & Anderson, 1997, of eastern Indo-Pacific origin, is recorded for the first time from the Mediterranean Sea. A small school of six individuals of this species were caught off Portopalo, Sicily, Italy in February 2017. Morphometric measurements and meristic traits are provided based on four specimens, and the possible vector of introduction of the species into the Mediterranean is briefly discussed. 

Chlorurus rhakoura Randall & Anderson, 1997 (Perciformes, Scaridae), an Indo-Pacific fish new for the Mediterranean Sea

The scarid fish Chlorurus rhakoura Randall & Anderson, 1997, of eastern Indo-Pacific origin, is recorded for the first time from the Mediterranean Sea. A small school of six individuals of this species were caught off Portopalo, Sicily, Italy in February 2017. Morphometric measurements and meristic traits are provided based on four specimens, and the possible vector of introduction of the species into the Mediterranean is briefly discussed. 

Proteolytic processing of the beta-amyloid precursor protein (APP) in membranes of the human neuroblastoma SH-SY5Y cells

Bibliothèques et publics, bibliothèques publiques dans l’Europe d’Ancien Régime (XVIe-XVIIIe siècle) - Yann Sordet (Bibliothèque Mazarine) 18hLiège, ULg, Grand Physique (Bât. A1) Organisation : Cycle de conférences de Transitions En savoir plus. Source de l'information : http://web.philo.ulg.ac.be/transitions/agenda-general

ISOLATION AND CHARACTERIZATION OF THE GM3 SYNTHASE cDNA FROM HUMAN PLACENTA

It is known that gangliosides have various important biological functions, and their functions as well as their biosynthesis are currently clarified (1, 2). In vertebrates, almost all the ganglio-series gangliosides are synthesized from a common precursor, ganglioside GM3, which has the simplest structure among the major gangliosides. GM3 itself is known to participate in induction of differentiation, modulation of proliferation, signal transduction and integrin-mediated cell adhesion. GM3 synthase (EC 2.4.99.9, ST3Gal V) is the enzyme involved in the last step of GM3 biosynthesis: it catalyses the transfer of a sialic acid moiety from CMP-sialic acid onto lactosylceramide, forming an a2-3 linkage. Whereas GM3 is ubiquitously distributed in the plasma membranes of all eukaryotic cells, GM3 synthase results expressed in a tissue specific manner, especially in brain, placenta, muscle and testis (3). Many important issues, such as human cDNA identification and characterization, genomic structure and regulation of gene expression, are still open. To isolate the coding sequence of the gene of GM3 synthase from human placenta we used the 5\u2019- and 3\u2019-Rapid Amplification of cDNA Ends technology (SMART RACE cDNA Amplification Kit, Clontech) using, as specific primers, oligonucleotides derived from the human GM3 synthase cDNA sequence from differentiated HL60 cells (3). The different PCR products were cloned into the pCR2.1 vector (TA Cloning Kit, InVitrogen) and the nucleotide sequence was determined. A cDNA, showing high sequence homology with that encoding the human GM3 synthase from TPA-differentiated HL60 cells (3), has been successfully isolated and cloned from human placenta. The major difference between these two cDNAs is in the 5\u2019-end, according to the existence of different promoter regions, responsible for tissue-specific expression of the gene. Furthermore, the cDNA from the human placenta contains, upstream and in frame with the ATG indicated as translation initiation site for the GM3 synthase of HL60 cells, another ATG codon inserted in a sequence compatible with Kozak\u2019s rule, suggesting that the protein of the human placenta has an additional portion in NH2-terminus. The complete coding region of the human placenta cDNA is going to be cloned in an expression vector, under the control of the CMV promoter, in order to evaluate its activity. On the other hand, in vitro translation experiments are going to be carried out to define the first start codon. 1) Hakomori S.I. (2000): Glycoconj. J. 17, 627-647 2) Kolter T. et al. (2002): J.Biol.Chem. 277, 25859-25862 3) Ishii A. et al. (1998): J.B.C. 273, 31652-3165

CLONING OF THE GM3 SYNTHASE cDNA FROM HUMAN PLACENTA AND GENOMIC ORGANISATION OF THE GENE

INTRODUCTION: Gangliosides are a large family of sialic acid-containing glycosphingolipids that play important roles in a large variety of biological processes. Both their functions and their biosynthetic pathways are currently clarified (1, 2). In vertebrates, almost all the ganglio-series gangliosides are synthesized from a common precursor, ganglioside GM3, which has the simplest structure among the major ganglioside. GM3 itself is known to participate in induction of differentiation, modulation of proliferation, signal transduction and integrin-mediated cell adhesion. GM3 synthase (EC 2.4.99.9, ST3Gal V) is the enzyme involved in the last step of GM3 biosynthesis: it catalyses the transfer of a sialic acid moiety from CMP-sialic acid onto lactosylceramide, forming an a2-3 linkage. Whereas GM3 is ubiquitously distributed in the plasma membranes of all eukaryotic cells, GM3 synthase results expressed in a tissue-specific manner, especially in brain, placenta, muscle and testis (3). Although its cDNA has been cloned from some mouse (4, 5) and human tissues (3, 6), studies on the genomic structure (7, 8) and on its transcriptional regulation (8, 9) provides contrasting results. MATERIALS AND METHODS: To isolate the complete coding sequence of the gene of GM3 synthase from human placenta we used the 5\u2019- and 3\u2019-Rapid Amplification of cDNA Ends technology (SMART RACE cDNA Amplification Kit, Clontech) using, as specific primers, oligonucleotides derived from the human GM3 synthase cDNA sequence from differentiated HL60 cells (3). The identity of some amplified DNA fragments was confirmed by Southern blot analysis (Gene ImagesTM AlkPhos DirectTM labelling and detection system, Amersham Pharmacia Biotech). The different PCR products were cloned into the pCR2.1 vector (TA Cloning Kit, InVitrogen) and the nucleotide sequence was determined (\u201cProgetto Camilla\u201d, M-Medical). The genomic structure of the human GM3 synthase gene has been determined through a human genome BLAST homology search of the public database (GenBank) using the GM3 synthase cDNA from human placenta as the query sequence. RESULTS: A cDNA, consisting of 2149 bp and showing high sequence homology with those encoding the human GM3 synthase from other human tissues (3, 6), has been successfully isolated and cloned from human placenta. Notwithstanding our approach, our cDNA has not the poli(A) tail. Between our cDNA and the other published ones, the major difference is in the 5\u2019-end, according to the existence of different promoter regions, responsible for tissue-specific expression of the gene. Furthermore, the cDNA from the human placenta contains, upstream and in frame with the ATG indicated as translation initiation site for the GM3 synthase of HL60 cells, another ATG codon inserted in a sequence compatible with Kozak\u2019s rule, suggesting that the protein of the human placenta could have an additional portion in NH2-terminus. The complete and partial coding regions of the human placenta cDNA are going to be cloned in an expression vector, under the control of the CMV promoter, in order to evaluate their GM3 synthase activity. The results of the human genome BLAST homology search of the public database using the GM3 synthase cDNA from human placenta as the query sequence showed that the gene consists of seven exons which span over 28.5 kb, with exons ranging in size up to 1242 bp. All exon-intron boundaries follows the GT-AG rule (10). 1) Hakomori S.I. (2000) Glycoconj. J. 17, 627-647 2) Kolter T. et al. (2002) J. Biol. Chem. 277, 25859-25862 3) Ishii A. et al. (1998) J. Biol. Chem. 273, 31652-31655 4) Kono M. et al. (1998) Biochem. Biophys. Res. Comm. 253, 170-175 5) Fukumoto S. et al. (1999) J. Biol. Chem. 274, 9271-9276 6) Kapitonov D. et al.(1999) Glycoconj J. 16, 337-350 7) Kim K.W. et al. (2001) Gene 273, 163-171 8) Kim S.W. et al. (2002) ) Biochim. Biophys. Acta 1578, 84-89 9) Zeng G. et al. (2003) Biochim. Biophys. Acta 1625, 30-35 10) Breathnach R. and Chambon P. (1981) Annu. Rev. Biochem. 50, 349-38

HUMAN ST3Gal V ISOFORMS, BOTH TARGETED TO GOLGI, DERIVE FROM USE OF TWO ALTERNATE TRANSLATION START SITES

ST3Gal V (or GM3 synthase) is the sialyltransferase that catalyses the initial step in the biosynthesis of most complex gangliosides from lactosylceramide. ST3Gal V plays a key regulatory role in determining the cell surface ganglioside profile and, consequently, in modulating a large variety of ganglioside-dependent cellular events, such as cell proliferation and differentiation, adhesion, apoptosis, oncogenesis. In addition, a homozygous loss-of-function mutation in the hST3Gal V gene is cause of an autosomal recessive infantile–onset symptomatic epilepsy syndrome. Recently, we have identified a hST3Gal V mRNA variant containing an additional translation start codon, located upstream and in-frame with that considered unique translation initiation site in the human GM3 synthase gene, providing the first evidence of the existence of two differentially N-terminal extended isoforms of the protein [1]. The functional relevance of the longer isoform has to be defined yet, and a study to define its sub-cellular localization could provide useful findings to approach this topic. Here, we have recombinantly expressed the c-myc C-terminal tagged longer isoform in COS-7 cells and verified its N-glycosylation state by treatment of transfected-cell lysates with PNGase F and endo-H; the protein expression and the glycosidase-digested products have been analyzed by western blot with anti-c-myc antibodies. Surprisingly, the transient transfection of COS-7 cells with the hST3Gal V cDNA corresponding to mRNA variant isolated by us resulted in the expression of both hST3Gal V isoforms suggesting the possibility of an alternate initiation of translation by context-dependent leaky scanning. The hypothesis has been confirmed by site-specific mutagenesis experiments. Results of PNGase F and endo-H treatments indicated that the longer isoform carries N-glycans of complex type as the shorter form, strongly supporting the conclusion that both isoforms are targeted to the Golgi. Analyses to determine eventual differences in the Golgi compartment (cis, medial, or trans) localization of the two hST3Gal V isoforms are in progress. 1. Berselli P et al, 2006, Human GM3 synthase: a new mRNA variant encodes an NH2-terminal extended form of the protein, Biochim Biophys Acta 1759, 348-35

GM3 IN THE REGULATION OF THE EXPRESSION AND ACTIVATION OF ErbB-2/EGFR HETERODIMERS

Gangliosides are a large and heterogeneous family of sialic acid containing glycosphingolipids, ubiquitous components of all eukaryotic cell membranes. They can partially segregate, together with cholesterol and specific signaling transduction proteins, such as receptor tyrosine-kinases, into unique more or less stable clusters or microdomains, indicated as \u201cglycolipid-enriched domains\u201d, \u201clipid rafts\u201d, \u201ccaveolae\u201d, contributing to the membrane structure, organization and function (1). Gangliosides are well-characterized modulators of receptor tyrosine-kinase (RTKs) phophorylation and dimerization (2). Our interest is particularly directed to study the relationship between gangliosides and two members of the tyrosine kinase ErbB receptor family: the epidermal growth factor receptor, EGFR or ErbB-1, and the structurally related protein ErbB-2. Unlike EGFR, ErbB-2 is a ligandless receptor: it can be activated by heterodimerization and cross-phosphorylation by other ligand-activated ErbB receptors (3,4). Our previous experimental evidence supports the functional relationship between ErbB-2 and gangliosides, in particular GM3 (5,6). In the present study, using the HC11 mouse mammary epithelial cell line, we investigated the ErbB-2 activation state and its tendency to form stable molecular complexes with EGFR and with ganglioside GM3, before and after EGF stimulation, by co-immunoprecipitation experiments with anti-ErbB-2 antibody and Western blot analyses. As HC11 cells express different ganglioside species, the exclusive association of GM3 with ErbB-2 and EGFR was ascertained by high performance-thin layer chromatography (HP-TLC) and TLC-immunostaining analyses of gangliosides extracted from the immunoprecipitates. Results display that in EGF-stimulated HC11 cells stable and tyrosine-phosphorylated ErbB2/EGFR dimers are formed and that GM3 is the unique ganglioside tightly associated to ErbB-2/EGFR dimers and to EGFR monomers, but not to ErbB2 monomers. In cells not stimulated with EGF a spontaneous but unproductive dimerization of ErbB2 and EGFR takes place and no ganglioside is found associated to the receptors. These observations indicate that the modulation of ErbB2 activation by GM3 may be mediated by EGFR, but that EGF stimulation is indispensable. After ganglioside depletion by [D]-PDMP, phosphorylated EGFR monomers are observed both before and after EGF stimulation, whereas ErbB-2 is present in the monomeric and unphosphorylated state even after EGF stimulation, suggesting that GM3 might have a bivalent key role in modulating the activation of ErbB-2 and EGFR. References 1. Fivaz, M., Abrami, L., Van Der Goot. F.G. Trends Cell Biol. 9(6), 212-213 (1999); 2. Bremer, E.G., Current topics in membranes 40, 387-411(1999); 3. Qian, X., LeVea, C.M., Freeman, J.K., Dougall, W.C., Greene, M.I., Proc. Natl. Acad. Sci. USA 91, 1500-1504 (1994); 4. Gulliford, T.J., Huang, G.C., Ouyang, X., Epstein, R.J., Oncogene 15, 2219-2223 (1997); 5. Sottocornola E., Berra B., and Colombo I., Biochim. Biophys. Acta-Molecolar and cell Biology of Lipids, 1635, 55-66 (2003); 6. Sottocornola E., Misasi R., Mattei V., Ciarlo L., Gradini R., Garofalo T., Berra B., Colombo I., and Sorice M., FEBS J. 273, 1821-1830 (2006)