Variation of major neutral oligosaccharides levels in human colostrum.

OBJECTIVES: Human colostrum is known to be important for the protection of infants against infection by pathogenic microorganisms. This protection is thought to be due, partially, to various neutral and acidic oligosaccharides that are present in colostrum and milk. However, the concentrations of each of the oligosaccharide of human colostrum have not yet been determined. The aim of this present study was to determine the concentration of each of the major neutral oligosaccharide for three consecutive days from the start of lactation. METHOD: We analyzed the level of each neutral oligosaccharide in human colostrum, for three consecutive days from the start of lactation, obtained from 12 healthy Japanese women (ranging in age from 21 to 35 years; primipara 6 and multipara 6). The ABO blood groups of the donors were determined: A, three; B, three; O, five; AB, one. The determined human milk oligosaccharides were 2'-fucosyllactose (2'-FL), 3-fucosyllactose (3-FL), lactodifucotetraose (LDFT), lacto-N-tetraose (LNT), lacto-N-neotetraose (LNnT), three lacto-N-fucopentaose (LNFP I, II and III) and two lacto-N-difucohexaose (LNFDH I and II) using high-performance liquid chromatography (HPLC) with two derivatization techniques. RESULTS: The concentrations of 2'-FL and LDFT in colostrum on day 1 were significantly higher than those on days 2 and 3 (P<0.05). An increase in LNT was observed on day 3 compared with day 1 (P<0.05). CONCLUSION: These changes in concentrations of 2'-FL, LDFT and LNT may reflect the requirements for prebiotics and anti-infection agents by human infants during early lactation.

Fundamental study of small interfering RNAs for ganglioside GD3 synthase gene as a therapeutic target of lung cancers.

Gangliosides GD3 and GD2 are specifically expressed in neuro-ectoderm-derived tumors, and are considered to play roles in the malignant properties of those cells. We analysed effects of small interfering (si) RNAs against GD3 synthase gene on the expression of ganglioside GD2 and biological phenotypes of human lung cancer cells expressing GD2. An siRNA could suppress the mRNA level of GD3 synthase gene even by single transfection, whereas repeated transfection was required to suppress GD2 expression on the cell surface. Significant reduction in the cell growth and invasion activity was observed in both lung cancer cell lines examined, when repeatedly transfected with the siRNA twice a week. DNA ladder formation was observed after third transfection, indicating the potent induction of apoptosis. Stable transfection of an RNAi expression vector with H1 RNA promoter was also examined. Transfectant cells with the RNAi expression vector showed almost equivalent suppression of GD2 expression and tumor properties in vitro. Furthermore, the stable transfectant cells showed slower cell growth than the control cells in severe combined immunodeficiency mice. These results suggested that siRNAs and/or RNAi expression vectors to generate siRNAs are promising approach to overcome human lung cancers.

Synthesis of functional aromatic multisulfonyl chlorides and their masked precursors.

The synthesis of functional aromatic bis(sulfonyl chlorides) containing an acetophenone and two sulfonyl chloride groups, i.e., 3,5-bis[4-(chlorosulfonyl)phenyl]-1-acetophenone (16), 3,5-bis(chlorosulfonyl)-1-acetophenone (17), and 3,5-bis(4-(chlorosulfonyl)phenyloxy)-1-acetophenone (18) via a sequence of reactions, involving in the last step the quantitative oxidative chlorination of S-(aryl)- N,N'-diethylthiocarbamate, alkyl- or benzyl thiophenyl groups as masked nonreactive precursors to sulfonyl chlorides is described. A related sequence of reactions was used for the synthesis of the aromatic trisulfonyl chloride 1,1,1-tris(4-chlorosulfonylphenyl)ethane (24). 4-(Chlorosulfonyl)phenoxyacetic acid, 2,2-bis[[[4-(chlorosulfonyl)phenoxyacetyl]oxy]methyl]-1,3-propanediyl ester (27), 5,11,17,23-tetrakis(chlorosulfonyl)-25,26,27,28-tetrakis(ethoxycarbonylmethoxy)calix[4]arene (38), 5,11,17,23,29,35-hexakis(chlorosulfonyl)-37,38,39,40,41,42-hexakis(ethoxycarbonylmethoxy)calix[6]arene (39), 5,11,17,23,29,35,41,47-octakis(chlorosulfonyl)-49,50,51,52,53,54,55,56-octakis(ethoxycarbonylmethoxy)calix[8]arene (40), 5,11,17,23-tetrakis(tert-butyl)-25,26,27,28-tetrakis(chlorosulfonyl phenoxyacetoxy)calix[4]arene (44), 5,11,17,23,29,35-hexakis(tert-butyl)-37,38,39,40,41,42-hexakis(chlorosulfonylphenoxyacetoxy)calix[6]arene (45), and 5,11,17,23,29,35,41,47-octakis(tert-butyl)-49,40,51,52,53,54,55,56-octakis(chlorosulfonylphenoxyacetoxy)calix[8]arene (46) were synthesized by two different multistep reaction procedures, the last step of both methods consisting of the chlorosulfonation of compounds containing suitable activated aromatic positions. 2,4,6-Tris(chlorosulfonyl)aniline (47) was obtained by the chlorosulfonation of aniline. The conformation of two series of multisulfonyl chlorides i.e., 38, 39, 40 and 44, 45, 46, was investigated by (1)H NMR spectroscopy. The masked nonreactive precursor states of the functional aromatic multisulfonyl chlorides and the aromatic multisulfonyl chlorides reported here represent the main starting building blocks required in a new synthetic strategy elaborated for the preparation of dendritic and other complex organic molecules.

Expression of glycoconjugates bearing the Lewis X epitope during neural differentiation of P19 EC cells.

The Lewis X (Le(x)) bearing glycolipids were noticeably increased in amounts during the course of neural differentiation of P19 EC cells induced by retinoic acid (RA, all-trans form). Applying neoglycolipid technology and in situ TLC-LSIMS, the oligosaccharide chains of these scarce Le(x) bearing glycolipids were partially characterized after released by endoglycoceramidase and subsequent conversion into neoglycolipids. In order to understand the enzymatic basis for the expression of Le(x) bearing glycolipids, we measured glycolipid, glycoprotein and oligosaccharide fucosyltransferase (Fuc-T) activities using appropriate substrates in P19 EC cells with or without RA treatment. All three Fuc-Ts were increased after RA treatment and the highest activity was in the differentiated neural cells. We then investigated the two possible Fuc-T genes that might be responsible for these changes using RT-PCR analysis. Mouse Fuc-TIX (mFuc-TIX) transcript was detected in all cell types but it was only strongly expressed in RA-induced aggregates and neural cells. In the case of mouse Fuc-TIV (mFuc-TIV) gene, its transcript was only detectable in RA-induced aggregates and not found in either undifferentiated or RA-induced neural cells. These results strongly support that RA induces only a transient expression of the mFuc-TIV gene in cell aggregates but a more persistent expression of the mFuc-TIX gene at the transcription level throughout neural cell differentiation. The mFuc-TIX gene is probably the main cause for the increased expression of Le(x) glycoconjugates during neural differentiation of P19 EC cells.

Connexin43 suppresses MFG-E8 while inducing contact growth inhibition of glioma cells.

Gap junction expression has been reported to control the growth of a variety of transformed cells. We undertook parallel analysis of connexins Cx32 and Cx43 in glioma cells, which revealed potential mechanisms underlying this phenomenon and led to several novel findings. Cx43, but not Cx32, suppressed C6 glioma cell growth. Paradoxically, Cx32 transfection resulted in severalfold more dye transfer than Cx43. However, Cx43 transfectants shared endogenous metabolites more efficiently than Cx32 transfectants. Interestingly, a significant portion of Cx43 permeants were incorporated into macromolecules more readily than those that transferred via Cx32. Cx43 induced contact inhibition of cell growth but in contrast to other reports, did not affect log phase growth rates. Cell death, senescence, or suppression of growth factor signaling was not involved because no significant alterations were seen in cell viability, telomerase, or mitogen-activated protein kinase activity. However, suppression of cell growth by Cx43 entailed the secretion of growth-regulatory factors. Most notably, a major component of conditioned medium that was affected by Cx43 was found to be MFG-E8 (milk fat globule epidermal growth factor 8), which is involved in cell anchorage and integrin signaling. These results indicate that Cx43 regulates cell growth by the modulation of extracellular growth factors including MFG-E8. Furthermore, the ability of a Cx to regulate cell growth may rely on its ability to mediate the intercellular transfer of endogenous metabolites but not artificial dyes.

Differential expression of two glucuronyltransferases synthesizing HNK-1 carbohydrate epitope in the sublineages of the rat myogenic progenitors.

HNK-1 epitope is a cell-surface carbohydrate mediating various cell-cell or cell-substrate interactions. We found HNK-1 epitope in longitudinally arrayed fibers in the subpopulation of the epaxial myotome, and hypaxial myoblasts migrating into the limb bud in the rat embryo. We next investigated the expression patterns of genes encoding two glucuronyltransferases (GlcAT-P, GlcAT-D) and sulfotransferase (Sul-T), which are required for biosynthesis of HNK-1 epitope. GlcAT-P gene was expressed in the non-migrating longitudinal fibers, whereas GlcAT-D gene was expressed in the migrating myoblasts in the limb bud. Sul-T gene expression was ubiquitously observed in all these myogenic populations. Thus, differential expression of GlcAT genes may relate to the epaxial/hypaxial or migrating/non-migrating myoblast lineages.

Identification of a stromal cell type characterized by the secretion of a soluble integrin-binding protein, MFG-E8, in mouse early gonadogenesis.

Mfge8 (milk fat globule-EGF-factor 8) encodes a soluble integrin-binding protein containing two Notch-like EGF domains and two discoidin domains. It mediates cell-to-cell interaction by binding to integrin alphavbeta3 via the RGD motif of its second EGF domain. Mfge8 was first expressed at 10.0 dpc in cells of the coelomic epithelium covering the mesonephros, and at 10.5 dpc Mfge8-expressing cells were found in the mesenchyme underneath the coelomic epithelium of the genital ridges. At 11.5-12.5 dpc, Mfge8 expressing cells were found in the stromal tissues subjacent to the coelomic epithelium that envelop the fetal gonad of both sexes. MFG-E8 protein was accumulated extracellularly in the interstitial tissues at the boundary of the mesonephros and the genital ridges. A comparison of the expression domains of Mfge8 and several gene markers showed that Mfge8 expression did not significantly overlap with the expression domain of Wt1 or Emx2, but partially with that of Lhx9 in 11.5-day XY gonads. Comparison of the expression pattern of Mfge8 with that of Hsd3beta1 in the 12.5-day testes revealed that the Mfge8-positive cells constitute a previously uncharacterized somatic cell type which is distinct from Sertoli cells, Leydig cells, peritubular myoid cells and the endothelial cells.

Involvement of gangliosides in glycosylphosphatidylinositol-anchored neuronal cell adhesion molecule TAG-1 signaling in lipid rafts.

The association of ganglioside GD3 with TAG-1, a glycosylphosphatidylinositol-anchored neuronal cell adhesion molecule, was examined by coimmunoprecipitation experiments. Previously, we have shown that the anti-ganglioside GD3 antibody (R24) immunoprecipitated the Src family kinase Lyn from the rat cerebellum, and R24 treatment of primary cerebellar cultures induced Lyn activation and rapid tyrosine phosphorylation of an 80-kDa protein (p80). We now report that R24 coimmunoprecipitates a 135-kDa protein (p135) from primary cerebellar cultures. Treatment with phosphatidylinositol-specific phospholipase C revealed that p135 was glycosylphosphatidylinositol-anchored to the membrane. It was identified as TAG-1 by sequential immunoprecipitation with an anti-TAG-1 antibody. Antibody-mediated cross-linking of TAG-1 induced Lyn activation and rapid tyrosine phosphorylation of p80. Selective inhibitor for Src family kinases reduced the tyrosine phosphorylation of p80. Sucrose density gradient analysis revealed that the TAG-1 and tyrosine-phosphorylated p80 in cerebellar cultures were present in the lipid raft fraction. These data show that TAG-1 transduces signals via Lyn to p80 in the lipid rafts of the cerebellum. Furthermore, degradation of cell-surface glycosphingolipids by endoglycoceramidase induced an alteration of TAG-1 distribution on an OptiPrep gradient and reduced the TAG-1-mediated Lyn activation and tyrosine phosphorylation of p80. These observations suggest that glycosphingolipids are involved in TAG-1-mediated signaling in lipid rafts.

Clinical usefulness of urine-based enzyme-linked immunosorbent assay for detection of antibody to Helicobacter pylori: a collaborative study in nine medical institutions in Japan.

BACKGROUND: A urine-based enzyme-linked immunosorbent assay (ELISA) kit for detection of antibody to Helicobacter pylori has been developed in Japan. Urine samples can be obtained noninvasively and are easier and safer to handle than are serum samples. The aim of this study was to examine the clinical usefulness of this urine-based ELISA kit. MATERIALS AND METHODS: A pair of random, single-void urine and serum samples was collected from each of 1,061 subjects, including 238 patients with gastroduodenal disease. The sensitivity and specificity of the urine-based ELISA was compared with those of three commercially available serum-based ELISA kits. For those patients with gastroduodenal disease, the urine- and serum-based ELISA results were also compared with those for other diagnostic methods using endoscopic biopsy specimens, such as culture, histology, and rapid urease tests. RESULTS: Based on the three serum-based ELISA results, the sensitivity, specificity, and accuracy of the urine-based ELISA were 97.7%, 95.6%, and 96.8%, respectively. On the basis of the biopsy test results, the sensitivity (96.2%), specificity (78.9%), and accuracy (91.0%) of the urine-based ELISA were almost equivalent or superior to all three serum-based ELISAs tested. In addition, 10 of the 12 false-positive cases for urine-based ELISA were confirmed to be true positives for antibodies to H. pylori by Western blot analysis and inhibition ELISA. CONCLUSIONS: The urine-based ELISA (URINELISA H. pylori Antibody) is very accurate and should be useful as an alternative to serum-based ELISAs for screening of H. pylori infection.

Expression of galectin-1 mRNA correlates with the malignant potential of human gliomas and expression of antisense galectin-1 inhibits the growth of 9 glioma cells.

Although its precise function has not yet been established, galectin-1 seems to play a role in tumor progression. In this study, we investigated galectin-1 mRNA expression in human glioma specimens and glioma cell lines. Northern blot analysis showed higher galectin-1 mRNA levels in glioma tissues. The 0.7-kb galectin-1 mRNA transcript was detected, and the expression level correlated with the malignant state, from low-grade astrocytoma to glioblastoma. In several human glioma specimens, immunohistochemical examination with antiserum against a synthetic peptide corresponding to the predicted C-terminal sequence of the protein showed high levels of galectin-1 expression. To clarify the correlation between the expression of galectin-1 and the malignancy of gliomas, we examined whether expression of antisense galectin-1 would suppress tumor growth in rat 9L cells that express high levels of galectin-1. The cells were transfected with a plasmid DNA that produces antisense galectin-1 mRNA under the control of the metallothionein promoter, and stable clones expressing low levels of galectin-1 protein in comparison with control clones were isolated. Cells with low levels of galectin-1 displayed dramatic phenotypic changes in their morphology and growth properties compared with vector-transfected control 9L cells. Our data suggest that decreased expression of galectin-1 may arrest the growth of rat 9L cells.

PKCeta associates with cyclin E/cdk2/p21 complex, phosphorylates p21 and inhibits cdk2 kinase in keratinocytes.

PKC is activated on the cell membrane by phospholipids, thereby transducing signals to intracellular pathways. We provide here another function of PKC, namely, regulating cell cycle by interaction with the cyclin E/cdk2/p21 complex. Among the 10 isoforms of PKC, PKCeta is predominantly expressed in squamous cell epithelia and induces terminal differentiation of keratinocytes. PKCeta that is endogenously expressed or overexpressed was found to associate with the cyclin E/cdk2/p21 complex in keratinocytes of mice and humans. Requirement of a possible adaptor protein to the binding was suggested by the reconstitution of PKCeta and the cyclin E/cdk2/p21 complex which were prepared from human keratinocytes or Sf9 insect cells. Colocalization of PKCeta with cdk2 and cyclin E was observed in the cytoplasm, particularly in the perinuclear region. p21 was phosphorylated in the complex in a PKC-activator dependent manner. Association of PKCeta with cdk2 resulted in marked inhibition of cdk2-kinase activity when measured by phosphorylation of Rb. Dominant negative PKCeta associated with the cyclin E/cdk2/p21 complex, but caused a little inhibition of cdk2 kinase activity. Among the known regulatory mechanisms of cdk2 activity, dephosphorylation of Thr160 was demonstrated. Oncogene (2000) 19, 6334 - 6341.

Functional roles of glycosphingolipids in signal transduction via lipid rafts.

The formation of glycosphingolipid (GSL)-cholesterol microdomains in cell membranes has been proposed to function as platforms for the attachment of lipid-modified proteins, such as glycosylphosphatidylinositol (GPI)-anchored proteins and src-family tyrosine kinases. The microdomains are postulated to be involved in GPI-anchored protein signaling via src-family kinase. Here, the functional roles of GSLs in signal transduction mediated by the microdomains are discussed. Antibodies against GSLs co-precipitate GPI-anchored proteins, src-family kinases and several components of the microdomains. Antibody-mediated crosslinking of GSLs, as well as that of GPI-anchored proteins, induces a rapid activation of src-family kinases and a transient increase in the tyrosine phosphorylation of several substrates. Enzymatic degradation of GSLs reduces the activation of src-family kinase and tyrosine phosphorylation by antibody-mediated crosslinking of GPI-anchored protein. Furthermore, GSLs can also modulate signal transduction of immunoreceptors and growth factor receptors in the microdomains. Thus, GSLs have important roles in signal transduction mediated by the microdomains.

Cloning and expression of a novel galactoside beta1, 3-glucuronyltransferase involved in the biosynthesis of HNK-1 epitope.

We isolated a cDNA encoding a novel glucuronyltransferase, designated GlcAT-D, involved in the biosynthesis of the HNK-1 carbohydrate epitope from rat embryo cDNA by the degenerate polymerase chain reaction method. The new cDNA sequence revealed an open reading frame coding for a protein of 324 amino acids with type II transmembrane protein topology. The amino acid sequence of GlcAT-D displayed 50.0% identity to rat GlcAT-P, which is involved in the biosynthesis of the HNK-1 epitope on glycoproteins. Expression of GlcAT-D in COS-7 cells resulted in the formation of the HNK-1 epitope on the cell surface. The enzyme expressed in COS-7 cells transferred a glucuronic acid (GlcA) not only to asialo-orosomucoid, a glycoprotein bearing terminal N-acetyllactosamine structure, but also to paragloboside (lacto-N-neotetraosylceramide), a precursor of the HNK-1 epitope on glycolipids. Furthermore, substrate specificity analysis using a soluble chimeric form of GlcAT-D revealed that GlcAT-D transfers a GlcA not only to Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc-pyridylamine++ + but also to Galbeta1-3GlcNAcbeta1-3Galbeta1-4Glc-pyridylamine++ +. Enzymatic hydrolysis and Smith degradation of the reaction product indicated that GlcAT-D transfers a GlcA through a beta1,3-linkage to a terminal galactose. The GlcAT-D transcripts were detected in embryonic, postnatal, and adult rat brain. In situ hybridization analysis revealed that the expression pattern of GlcAT-D transcript in embryo is similar to that of GlcAT-P, but distinct expression of GlcAT-D was observed in the embryonic pallidum and retina. Regions that expressed GlcAT-D and/or GlcAT-P were always HNK-1-positive, indicating that both GlcATs are involved in the synthesis of the HNK-1 epitope in vivo.

Possible roles of glycosphingolipids in lipid rafts.

Recent studies have suggested that glycosphingolipid (GSL)-cholesterol microdomains in cell membranes may function as platforms for the attachment of lipid-modified proteins, such as glycosylphosphatidylinositol (GPI)-anchored proteins and src-family tyrosine kinases. The microdomains are proposed to be involved in membrane trafficking of GPI-anchored proteins and in signal transduction via src-family kinases. Here, the possible roles of GSLs in the physical properties of these microdomains, as well as in membrane trafficking and signal transduction, are discussed. Sphingolipid depletion inhibits the intracellular transport of GPI-anchored proteins in biosynthetic traffic and endocytosis via GPI-anchored proteins. Antibodies against GSLs as well as GPI-anchored proteins co-precipitate src-family kinases. Antibody-mediated cross-linking of GSLs, as well as that of GPI-anchored proteins, induces a transient increase in the tyrosine phosphorylation of several substrates. Thus, GSLs have important roles in lipid rafts.

Expression cloning and functional characterization of human cDNA for ganglioside GM3 synthase.

Ganglioside GM3 is a major glycosphingolipid in the plasma membrane and is widely distributed in vertebrates. We describe here the isolation of a human cDNA whose protein product is responsible for the synthesis of GM3. The cloned cDNA spanned 2,359 base pairs, with an open reading frame encoding a protein of 362 amino acids with a predicted molecular mass of 41.7 kDa. The deduced primary structure shows features characteristic of the sialyltransferase family, including a type II transmembrane topology and the sialylmotifs L at the center and S at the C-terminal region. An amino acid substitution from aspartic acid to histidine was demonstrated at a position invariant in sialylmotif L of all the other sialyltransferases so far cloned. The best acceptor substrate for the gene product was lactosylceramide, and cells transfected with the cloned cDNA clearly exhibited de novo synthesis of GM3, with a measurable decrease in the precursor lactosylceramide. Despite the ubiquitous distribution of ganglioside GM3 in human tissues, a major 2.4-kilobase transcript of the gene was found in a tissue-specific manner, with predominant expression in brain, skeletal muscle, and testis, and very low expression in liver.

Association of Src family tyrosine kinase Lyn with ganglioside GD3 in rat brain. Possible regulation of Lyn by glycosphingolipid in caveolae-like domains.

Association of gangliosides with specific proteins in the central nervous system was examined by co-immunoprecipitation with anti-ganglioside antibody. Protein kinase activity was detected in precipitates with monoclonal antibody to ganglioside GD3 (R24) from membranal fraction of rat brain. Using in vitro kinase assay, several phosphorylated proteins of 40, 53, 56, and 80 kDa were isolated by gel electrophoresis. Of these proteins, the proteins of 53 and 56 kDa (p53/56) were identified as two isoforms of Src family tyrosine kinase Lyn, based on co-migration during gel electrophoresis, comparative peptide mapping, and sequential immunoprecipitation with anti-Lyn antibody. The identification was confirmed using a cDNA expression system in Chinese hamster ovary (CHO) cells, which express solely ganglioside GM3, the enzymatic substrate of GD3 synthase. In co-transfection with GD3 synthase and Lyn expression plasmids, R24 immunoprecipitated Lyn and anti-Lyn antibody immunoprecipitated GD3. R24 treatment of rat primary cerebellar cultures induced Lyn activation and rapid tyrosine phosphorylation of several substrates including mitogen-activated protein kinases. Furthermore, sucrose density gradient analysis showed that Lyn of cerebellum and CHO transfectants were detected in a low density light-scattering band, i.e. the caveolae membrane fraction. R24 immunoprecipitated caveolin from Triton X-100 extract of CHO transfectants. These observations suggest that GD3 may regulate Lyn in a caveolae-like domain on brain cell membranes.

Glycolipid sialyltransferases are enhanced during neural differentiation of mouse embryonic carcinoma cells, P19.

We have studied ganglioside alterations and their enzymatic basis during the course of neural differentiation of mouse embryonic carcinoma cell line P19. This cell line can differentiate into neurons and astrocytes on cell aggregation after treatment with retinoic acid (RA) or into muscle cells on dimethyl sulfoxide (DMSO) treatment. GD3, detected on immunostaining after thin-layer chromatography (TLC) with monoclonal antibody (MAb) R24, was markedly present in aggregates treated with RA. GM3 synthase (alpha 2,3-sialyltransferase, SAT-I) in neurons was found to exhibit the highest activity. GD3 synthase (alpha 2,8-sialyltransferase, SAT-II) and GD3 synthase mRNA, as analyzed by Northern blotting, were also markedly present in aggregates and neurons induced by RA. However, on treatment with DMSO, which induces muscle cells, there was no change in the level of GD3 synthase activity, and its transcript was hardly detected during the course of muscle differentiation. GT1b synthase (alpha 2,3-sialyltransferase, SAT-IV) was present at similar levels in undifferentiated cells and aggregates treated with RA, but a higher level was observed in neurons. On the other hand, the level of GQ1b synthase (alpha 2,8-sialyltransferase, SAT-V) in RA-induced aggregates was significantly higher than that in neurons. These results show that RA but not DMSO induces the expression of GM3, GD3, GT1b and GQ1b synthases, and particularly GD3 synthase mRNA, in the ganglioside biosynthetic pathway during the neural differentiation of embryonic carcinoma P19 cells.

The molecular cloning and expression of alpha 2,8-sialyltransferase (GD3 synthase) in a rat brain.

We have cloned the cDNA for a GD3 synthase (alpha-2,8-sialyltransferase, [EC 2.4.99.8]) from a rat embryonic brain cDNA library. Mammalian cells transfected with the cloned cDNA expressed GD3 on the cell surface and showed GD3 synthase activity. The deduced protein (342 amino acid residues) was predicted to have a type II membrane topology containing the "sialyl motif" and was found to be 91% similar to its human homologue. Analysis of the acceptor specificity of GD3 synthase protein indicated that this enzyme catalyzed the biosynthesis of GT1a and GQ1b as well as GD3. Northern blot analyses showed that the GD3 synthase gene is preferentially transcribed in the brain and the spleen. The expression of GD3 synthase mRNA was developmentally regulated, with the highest level in the brain during embryonic days 15 to 18. In situ hybridization analyses demonstrated that the GD3 synthase is strongly expressed in the ventricular/subventricular zone of the embryonic rat brain and retina. In the adult rat, GD3 synthase mRNA was detected in the cerebral cortex, hippocampus, thalamus, and cerebellum. These studies show that the spatio- and stage-restricted expression of GD3 in the developing rat brain may be regulated in part by the level of GD3 synthase mRNA.