Murine equivalent of the human histo-blood group ABO gene is a cis-AB gene and encodes a glycosyltransferase with both A and B transferase activity

Splicing transcriptome-wide association study to identify splicing events for pancreatic cancer risk

A large proportion of the heritability of pancreatic cancer risk remains elusive, and the contribution of specific mRNA splicing events to pancreatic cancer susceptibility has not been systematically evaluated. In this study, we performed a large splicing transcriptome-wide association study (spTWAS) using three modeling strategies (Enet, LASSO and MCP) to develop alternative splicing genetic prediction models for identifying novel susceptibility loci and splicing introns for pancreatic cancer risk by assessing 8275 pancreatic cancer cases and 6723 controls of European ancestry. Data from 305 subjects of whom the majority are of European descent in the Genotype-Tissue Expression Project (GTEx) were used and both cis-acting and promoter-enhancer interaction regions were considered to build these models. We identified nine splicing events of seven genes (ABO, UQCRC1, STARD3, ETAA1, CELA3B, LGR4 and SFT2D1) that showed an association of genetically predicted expression with pancreatic cancer risk at a false discovery rate ≤0.05. Of these genes, UQCRC1 and LGR4 have not yet been reported to be associated with pancreatic cancer risk. Fine-mapping analyses supported likely causal associations corresponding to six splicing events of three genes (P4HTM, ABO and PGAP3). Our study identified novel genes and splicing events associated with pancreatic cancer risk, which can improve our understanding of the etiology of this deadly malignancy.

Sex, T Cells, and the Microbiome in Natural ABO Antibody Production in Mice

BACKGROUND

"Natural" ABO antibodies (Abs) are produced without known exposure to A/B carbohydrate antigens, posing significant risks for hyperacute rejection during ABO-incompatible transplantation. We investigated anti-A "natural" ABO antibodies versus intentionally induced Abs with regard to the need for T-cell help, the impact of sex, and stimulation by the microbiome.

METHODS

Anti-A was measured by hemagglutination assay of sera from untreated C57BL/6 wild-type (WT) or T cell-deficient mice of both sexes. Human ABO-A reagent blood cell membranes were injected intraperitoneally to induce anti-A Abs. The gut microbiome was eliminated by maintenance of mice in germ-free housing.

RESULTS

Compared with WT mice, CD4 + T-cell knockout (KO), major histocompability complex-II KO, and αβ/γδ T-cell receptor KO mice produced much higher levels of anti-A nAbs; females produced dramatically more anti-A nAbs than males, rising substantially with puberty. Sensitization with human ABO-A reagent blood cell membranes did not induce additional anti-A in KO mice, unlike WT. Sex-matched CD4 + T-cell transfer significantly suppressed anti-A nAbs in KO mice and rendered mice responsive to A-sensitization. Even under germ-free conditions, WT mice of several strains produced anti-A nAbs, with significantly higher anti-A nAbs levels in females than males.

CONCLUSIONS

Anti-A nAbs were produced without T-cell help, without microbiome stimulation, in a sex- and age-dependent manner, suggestive of a role for sex hormones in regulating anti-A nAbs. Although CD4 + T cells were not required for anti-A nAbs, our findings indicate that T cells regulate anti-A nAb production. In contrast to anti-A nAbs, induced anti-A production was T-cell dependent without a sex bias.

Mechanisms of Formation of Antibodies against Blood Group Antigens That Do Not Exist in the Body

The system of the four different human blood groups is based on the oligosaccharide antigens A or B, which are located on the surface of blood cells and other cells including endothelial cells, attached to the membrane proteins or lipids. After transfusion, the presence of these antigens on the apical surface of endothelial cells could induce an immunological reaction against the host. The final oligosaccharide sequence of AgA consists of Gal-GlcNAc-Gal (GalNAc)-Fuc. AgB contains Gal-GlcNAc-Gal (Gal)-Fuc. These antigens are synthesised in the Golgi complex (GC) using unique Golgi glycosylation enzymes (GGEs). People with AgA also synthesise antibodies against AgB (group A [II]). People with AgB synthesise antibodies against AgA (group B [III]). People expressing AgA together with AgB (group AB [IV]) do not have these antibodies, while people who do not express these antigens (group O [0; I]) synthesise antibodies against both antigens. Consequently, the antibodies are synthesised against antigens that apparently do not exist in the body. Here, we compared the prediction power of the main hypotheses explaining the formation of these antibodies, namely, the concept of natural antibodies, the gut bacteria-derived antibody hypothesis, and the antibodies formed as a result of glycosylation mistakes or de-sialylation of polysaccharide chains. We assume that when the GC is overloaded with lipids, other less specialised GGEs could make mistakes and synthesise the antigens of these blood groups. Alternatively, under these conditions, the chylomicrons formed in the enterocytes may, under this overload, linger in the post-Golgi compartment, which is temporarily connected to the endosomes. These compartments contain neuraminidases that can cleave off sialic acid, unmasking these blood antigens located below the acid and inducing the production of antibodies.

The stem region of group A transferase is crucial for its specificity, and its alteration promotes heterologous Forssman synthase activity

Some stem region mutants of human blood group A transferase (hAT) possess Forssman synthase (FS) activity, but very little is known about the mechanisms responsible for this enzymatic crosstalk. We performed confocal microscopy and image analysis to determine whether different intra-Golgi localization was accountable for this acquired activity. We also performed structural modeling and mutational and normal mode analyses. We introduced new mutations in the stem region and tested its FS and AT activities. No differences in subcellular localization were found between hAT and FS-positive mutants. AlphaFold models of hAT and mFS (mouse Forssman synthase) showed that the hAT stem region has a tether-like stem region, while in mFS, it encircles its catalytic domain. In silico analysis of FS-positive mutants indicated that stem region mutations induced structural changes, decreasing interatomic interactions and mobility of hAT that correlated with FS activity. Several additional mutations introduced in that region also bestowed FS activity without altering the AT activity: hAT 37-55 aa substitution by mFS 34-52, 37-55 aa deletion, and missense mutations: S46P, Q278Y, and Q286M. Stem region structure, mobility, and interactions are crucial for hAT specificity. Moreover, stem region mutations can lead to heterologous Forssman activity without changes in the catalytic machinery.

ABO blood group antigens and differential glycan expression: Perspective on the evolution of common human enzyme deficiencies

Enzymes catalyze biochemical reactions and play critical roles in human health and disease. Enzyme variants and deficiencies can lead to variable expression of glycans, which can affect physiology, influence predilection for disease, and/or directly contribute to disease pathogenesis. Although certain well-characterized enzyme deficiencies result in overt disease, some of the most common enzyme deficiencies in humans form the basis of blood groups. These carbohydrate blood groups impact fundamental areas of clinical medicine, including the risk of infection and severity of infectious disease, bleeding risk, transfusion medicine, and tissue/organ transplantation. In this review, we examine the enzymes responsible for carbohydrate-based blood group antigen biosynthesis and their expression within the human population. We also consider the evolutionary selective pressures, e.g. malaria, that may account for the variation in carbohydrate structures and the implications of this biology for human disease.

Mixed-Up Sugars: Glycosyltransferase Cross-Reactivity in Cancerous Tissues and Their Therapeutic Targeting

The main categories of glycan changes in cancer are: (1) decreased expression of histo-blood group A and/or B antigens and increased Lewis-related antigens, (2) appearance of cryptic antigens, such as Tn and T, (3) emergence of genetically incompatible glycans, such as A antigen expressed in tumors of individuals of group B or O and heterophilic expression of Forssman antigen (FORS1), and (4) appearance of neoglycans. This review focuses on the expression of genetically incompatible A/B/FORS1 antigens in cancer. Several possible molecular mechanisms are exemplified, including missense mutations that alter the sugar specificity of A and B glycosyltransferases (AT and BT, respectively), restoration of the correct codon reading frame of O alleles, and modification of acceptor specificity of AT to synthesize the FORS1 antigen by missense mutations and/or altered splicing. Taking advantage of pre-existing natural immunity, the potential uses of these glycans for immunotherapeutic targeting will also be discussed.

Genetic Studies of Natural Glycosphingolipid Ligands for NKT Cells

Glycosphingolipids (GSL) are natural ligands of NKT cells. Several laboratories have reported the in vitro activity of isoglobotriosylceramide (iGb3) in stimulating NKT cells. However, the knockout mice of iGb3 synthase showed no deficiency in development and function of NKT cells. There is a lack of knowledge on the genetics of redundant natural glycosphingolipid ligands. We have identified additional glycosphingolipid with stimulatory activity to NKT cells, including fucosyl lactosylceramide (H antigen). Here we describe the procedures to generate mice with deficiencies in Fut1, Fut2, and Sec1 genes to deplete H antigen through BAC engineering for the generation of ES cell-targeting construct, as well as the mice with deficiency of both blood group H-GSL ligand and isoglobotriosylceramide.

Loss and Reappearance of A Antigen After Chemotherapy Leading to Blood Group Discrepancy in Acute Myeloid Leukemia: A Case Report

A male patient aged 11 years diagnosed with acute myeloid leukemia presented with complaints of fever, lethargy, and bleeding manifestations. On ordering red blood cells and platelet transfusion, his blood group was tested. Blood group discrepancy was observed in that forward grouping showed the O Rh D positive blood group and reverse grouping revealed the A Rh D positive. The patient's previous blood group record was O Rh D positive, and he had a transfusion history of O Rh D positive red blood cells and platelets in other hospital. Initial immunohematological workup results, including adsorption and heat elution, were consistent with the O Rh D-positive blood group, but further workups on follow-up after the commencement of chemotherapy showed that his original blood group was A Rh D positive, in which the A antigen expression was previously masked by the underlying disease condition of the patient. Hence, the correlation of laboratory results with clinical details and case history is an essential step in resolving such blood group discrepancies.

Promiscuity and specificity of eukaryotic glycosyltransferases

Glycosyltransferases are a large family of enzymes responsible for covalently linking sugar monosaccharides to a variety of organic substrates. These enzymes drive the synthesis of complex oligosaccharides known as glycans, which play key roles in inter-cellular interactions across all the kingdoms of life; they also catalyze sugar attachment during the synthesis of small-molecule metabolites such as plant flavonoids. A given glycosyltransferase enzyme is typically responsible for attaching a specific donor monosaccharide, via a specific glycosidic linkage, to a specific moiety on the acceptor substrate. However these enzymes are often promiscuous, able catalyze linkages between a variety of donors and acceptors. In this review we discuss distinct classes of glycosyltransferase promiscuity, each illustrated by enzymatic examples from small-molecule or glycan synthesis. We highlight the physical causes of promiscuity, and its biochemical consequences. Structural studies of glycosyltransferases involved in glycan synthesis show that they make specific contacts with ‘recognition motifs’ that are much smaller than the full oligosaccharide substrate. There is a wide range in the sizes of glycosyltransferase recognition motifs: highly promiscuous enzymes recognize monosaccharide or disaccharide motifs across multiple oligosaccharides, while highly specific enzymes recognize large, complex motifs found on few oligosaccharides. In eukaryotes, the localization of glycosyltransferases within compartments of the Golgi apparatus may play a role in mitigating the glycan variability caused by enzyme promiscuity.

Glycan diversity in the course of vertebrate evolution

Vertebrates are estimated to have arisen over 500 million years ago in the Cambrian Period. Species that survived the Big Five extinction events at a global scale underwent repeated adaptive radiations along with habitat expansions from the sea to the land and sky. The development of the endoskeleton and neural tube enabled more complex body shapes. At the same time, vertebrates became suitable for the invasion and proliferation of foreign organisms. Adaptive immune systems were acquired for responses to a wide variety of pathogens, and more sophisticated systems developed during the evolution of mammals and birds. Vertebrate glycans consist of common core structures and various elongated structures, such as Neu5Gc, Galα1-3Gal, Galα1-4Gal, and Galβ1-4Gal epitopes, depending on the species. During species diversification, complex glycan structures were generated, maintained or lost. Whole-genome sequencing has revealed that vertebrates harbor numerous and even redundant glycosyltransferase genes. The production of various glycan structures is controlled at the genetic level in a species-specific manner. Because cell surface glycans are often targets of bacterial and viral infections, glycan structural diversity is presumed to be protective against infections. However, the maintenance of apparently redundant glycosyltransferase genes and investment in species-specific glycan structures, even in higher vertebrates with highly developed immune systems, are not well explained. This fact suggests that glycans play important roles in unknown biological processes.

ABO blood group A transferase and its codon 69 substitution enzymes synthesize FORS1 antigen of FORS blood group system

Human histo-blood group A transferase (AT) catalyzes the biosynthesis of oligosaccharide A antigen important in blood transfusion and cell/tissue/organ transplantation. This enzyme may synthesize Forssman antigen (FORS1) of the FORS blood group system when exon 3 or 4 of the AT mRNA is deleted and/or the LeuGlyGly tripeptide at codons 266–268 of AT is replaced by GlyGlyAla. The Met69Ser/Thr substitutions also confer weak Forssman glycolipid synthase (FS) activity. In this study, we prepared the human AT derivative constructs containing any of the 20 amino acids at codon 69 with and without the GlyGlyAla substitution, transfected DNA to newly generated COS1(B3GALNT1 + A4GALT) cells expressing an enhanced level of globoside (Gb4), the FS acceptor substrate, and immunologically examined the FORS1 expression. Our results showed that all those substitution constructs at codon 69 exhibited FS activity. The combination with GlyGlyAla significantly increased the activity. The conserved methionine residue in the ABO, but not GBGT1, gene-encoded proteins may implicate its contribution to the separation of these genes in genetic evolution. Surprisingly, with increased Gb4 availability, the original human AT with the methionine residue at codon 69 was also demonstrated to synthesize FORS1, providing another molecular mechanism of FORS1 appearance in cancer of ordinary FORS1-negative individuals.

Biologic roles of the ABH and Lewis histo-blood group antigens part II: thrombosis, cardiovascular disease and metabolism

The ABH and Lewis antigens were among the first of the human red blood cell polymorphisms to be identified and, in the case of the former, play a dominant role in transfusion and transplantation. But these two therapies are largely twentieth-century innovations, and the ABH and related carbohydrate antigens are not only expressed on a very wide range of human tissues, but were present in primates long before modern humans evolved. Although we have learned a great deal about the biochemistry and genetics of these structures, the biological roles that they play in human health and disease are incompletely understood. This review and its companion, which appeared in a previous issue of Vox Sanguinis, will focus on a few of the biologic and pathologic processes which appear to be affected by histo-blood group phenotype. The first of the two reviews explored the interactions of two bacteria with the ABH and Lewis glycoconjugates of their human host cells, and described the possible connections between the immune response of the human host to infection and the development of the AB-isoagglutinins. This second review will describe the relationship between ABO phenotype and thromboembolic disease, cardiovascular disease states, and general metabolism.

Amino acid substitutions at sugar-recognizing codons confer ABO blood group system-related α1,3 Gal(NAc) transferases with differential enzymatic activity

Functional paralogous ABO, GBGT1, A3GALT2, and GGTA1 genes encode blood group A and B transferases (AT and BT), Forssman glycolipid synthase (FS), isoglobotriaosylceramide synthase (iGb3S), and α1,3-galactosyltransferase (GT), respectively. These glycosyltransferases transfer N-acetyl-d-galactosamine (GalNAc) or d-galactose forming an α1,3-glycosidic linkage. However, their acceptor substrates are diverse. Previously, we demonstrated that the amino acids at codons 266 and 268 of human AT/BT are crucial to their distinct sugar specificities, elucidating the molecular genetic basis of the ABO glycosylation polymorphism of clinical importance in transfusion and transplantation medicine. We also prepared in vitro mutagenized ATs/BTs having any of 20 possible amino acids at those codons, and showed that those codons determine the transferase activity and sugar specificity. We have expanded structural analysis to include evolutionarily related α1,3-Gal(NAc) transferases. Eukaryotic expression constructs were prepared of AT, FS, iGb3S, and GT, possessing selected tripeptides of AT-specific AlaGlyGly or LeuGlyGly, BT-specific MetGlyAla, FS-specific GlyGlyAla, or iGb3S and GT-specific HisAlaAla, at the codons corresponding to 266–268 of human AT/BT. DNA transfection was performed using appropriate recipient cells existing and newly created, and the appearance of cell surface oligosaccharide antigens was immunologically examined. The results have shown that several tripeptides other than the originals also bestowed transferase activity. However, the repertoire of functional amino acids varied among those transferases, suggesting that structures around those codons differentially affected the interactions between donor nucleotide-sugar and acceptor substrates. It was concluded that different tripeptide sequences at the substrate-binding pocket have contributed to the generation of α1,3-Gal(NAc) transferases with diversified specificities.

ABO phenotype-protected reproduction based on human specific α1,2 L-fucosylation as explained by the Bombay type formation

The metabolic relationship between the formation of the ABO(H) blood group phenotype and human fertility is evident in the case of the (Oh) or Bombay blood type, which Charles Darwin would have interpreted as resulting from reduced male fertility in consanguinities, based on the history of his own family, the Darwin/Wedgwood Dynasty. The classic Bombay type occurs with the extremely rare, human-specific genotype (h/h; se/se), which (due to point mutations) does not encode fucosyltransferases 1(FUT1) and 2 (FUT2). These enzymes are the basis for ABO(H) phenotype formation on the cell surfaces and fucosylation of plasma proteins, involving neonatal immunoglobulin M (IgM). In the normal human blood group O(H), which is not protected by clonal selection with regard to environmental A/B immunization, the plasma contains a mixture of non-immune and adaptive anti-A/B reactive isoagglutinins, which in the O(h) Bombay type show extremely elevated levels, associated with decreased levels of fucosylation-dependent functional plasma proteins, suchs as the van Willebrand factor (vWF) and clotting factor VIII. In fact, while the involvement of adaptive immunoglobulins remains unknown, poor fucosylation may explain the polyreactivity in the Bombay type plasma, which exhibits pronounced complement-binding cross-reactive anti-A/Tn and anti-B IgM levels, with additional anti-H reactivity, acting over a wide range of temperatures, with an amplitude at 37 °C. This aggressive anti-glycan-reactive IgM molecule suggests the induction of ADCC (antibody-dependent) and/or complement-mediated cytotoxicity via overexpressed glycosidic bond sites against the embryogenic stem cell-to-germ cell transformation, which is characterized by fleeting appearances of A-like, developmental trans-species GalNAcα1-O-Ser/Thr-R glycan, also referred to as the Tn (T "nouvelle") antigen.

Blood group ABO gene-encoded A transferase catalyzes the biosynthesis of FORS1 antigen of FORS system upon Met69Thr/Ser substitution

Blood group A/B glycosyltransferases (AT/BTs) and Forssman glycolipid synthase (FS) are encoded by the evolutionarily related ABO (A/B alleles) and GBGT1 genes, respectively. AT/BT and FS catalyze the biosynthesis of A/B and Forssman (FORS1) oligosaccharide antigens that are responsible for the distinct blood group systems of ABO and FORS. Using genetic engineering, DNA transfection, and immunocytochemistry and immunocytometry, we have previously shown that the eukaryotic expression construct encoding human AT, whose LeuGlyGly tripeptide at codons 266 to 268 was replaced with FS-specific GlyGlyAla tripeptide, induced weak appearance of FORS1 antigen. Recently, we have shown that the human AT complementary DNA constructs deleting exons 3 or 4, but not exons 2 or 5, induced moderate expression of FORS1 antigen. The constructs containing both the GlyGlyAla substitution and the exon 3 or 4 deletion exhibited an increased FS activity. Here, we report another molecular mechanism in which an amino acid substitution at codon 69 from methionine to threonine or serine (Met69Thr/Ser) also modified enzymatic specificity and permitted FORS1 biosynthesis. Considering that codon 69 is the first amino acid of exon 5 and that the cointroduction of Met69Thr and GlyGlyAla substitutions also enhanced FS activity, the methionine substitutions may affect enzyme structure in a mode similar to the exon 3 or 4 deletion but distinct from the GlyGlyAla substitution.

ABO blood group A transferases catalyze the biosynthesis of FORS blood group FORS1 antigen upon deletion of exon 3 or 4

Evolutionarily related ABO and GBGT1 genes encode, respectively, A and B glycosyltransferases (AT and BT) and Forssman glycolipid synthase (FS), which catalyze the biosynthesis of A and B, and Forssman (FORS1) oligosaccharide antigens responsible for the ABO and FORS blood group systems. Humans are a Forssman antigen-negative species; however, rare individuals with A_pae phenotype express FORS1 on their red blood cells. We previously demonstrated that the replacement of the LeuGlyGly tripeptide sequence at codons 266 to 268 of human AT with GBGT1-encoded FS-specific GlyGlyAla enabled the enzyme to produce FORS1 antigen, although the FS activity was weak. We searched for additional molecular mechanisms that might allow human AT to express FORS1. A variety of derivative expression constructs of human AT were prepared. DNA was transfected into COS1 (B3GALNT1) cells, and cell-surface expression of FORS1 was immunologically monitored. To our surprise, the deletion of exon 3 or 4, but not of exon 2 or 5, of human AT transcripts bestowed moderate FS activity, indicating that the A allele is inherently capable of producing a protein with FS activity. Because RNA splicing is frequently altered in cancer, this mechanism may explain, at least partially, the appearance of FORS1 in human cancer. Furthermore, strong FS activity was attained, in addition to AT and BT activities, by cointroducing 1 of those deletions and the GlyGlyAla substitution, possibly by the synergistic effects of altered intra-Golgi localization/conformation by the former and modified enzyme specificity by the latter.

Sequence analysis of ABO and its homologues is valid for species identification

BACKGROUND

ABO and its paralogues, such as A3GALT2 and GGTA1, encoding α1,3-Gal(NAc) transferases, belong to the glycosyltransferase 6 (GT6) gene family. We have developed an alternative method for the identification of species based on sequence variations within the GT6 gene family, which is applicable to degraded DNA.

METHODS/MATERIALS

DNA samples prepared from control mammalian species, together with an unknown sample, were polymerase chain reaction (PCR)-amplified using one universal primer pair targeting the sequences in the last coding exons of the GT6 gene family, yielding 141-bp products derived from those multiple loci. After cloning, sequence determination and Basic Local Alignment Search Tool analysis, phylogenetic trees were constructed.

RESULTS

Comparison of the sequences obtained with those references showed good concordance with each of the starting species of mammals. This system was able to identify 'mouse' or 'rodent' as the origin of the unknown sample.

CONCLUSION

For the identification of species, genotyping of ABO and its homologues would be applicable for the analysis of degraded DNA samples. Although the method employed in this study is likely valid for mammals, it would not be suitable for birds, fish and reptiles. It may be possible to improve the present method for use with other species by employing an alternative universal primer set.

Evolutionary divergence of the ABO and GBGT1 genes specifying the ABO and FORS blood group systems through chromosomal rearrangements

Human alleles at the ABO and GBGT1 genetic loci specify glycosylation polymorphism of ABO and FORS blood group systems, respectively, and their allelic basis has been elucidated. These genes are also present in other species, but presence/absence, as well as functionality/non-functionality are species-dependent. Molecular mechanisms and forces that created this species divergence were unknown. Utilizing genomic information available from GenBank and Ensembl databases, gene order maps were constructed of a chromosomal region surrounding the ABO and GBGT1 genes from a variety of vertebrate species. Both similarities and differences were observed in their chromosomal organization. Interestingly, the ABO and GBGT1 genes were found located at the boundaries of chromosomal fragments that seem to have been inverted/translocated during species evolution. Genetic alterations, such as deletions and duplications, are prevalent at the ends of rearranged chromosomal fragments, which may partially explain the species-dependent divergence of those clinically important glycosyltransferase genes.

Early ovariectomy reveals the germline encoding of natural anti-A- and Tn-cross-reactive immunoglobulin M (IgM) arising from developmental O-GalNAc glycosylations. (Germline-encoded natural anti-A/Tn cross-reactive IgM)

While native blood group A-like glycans have not been demonstrated in prokaryotic microorganisms as a source of human "natural" anti-A isoagglutinin production, and metazoan eukaryotic N-acetylgalactosamine O-glycosylation of serine or threonine residues (O-GalNAc-Ser/Thr-R) does not occur in bacteria, the O-GalNAc glycan-bearing ovarian glycolipids, discovered in C57BL/10 mice, are complementary to the syngeneic anti-A-reactive immunoglobulin M (IgM), which is not present in animals that have undergone ovariectomy prior to the onset of puberty. These mammalian ovarian glycolipids are complementary also to the anti-A/Tn cross-reactive Helix pomatia agglutinin (HPA), a molluscan defense protein, emerging from the coat proteins of fertilized eggs and reflecting the snail-intrinsic, reversible O-GalNAc glycosylations. The hexameric structure of this primitive invertebrate defense protein gives rise to speculation regarding an evolutionary relationship to the mammalian nonimmune, anti-A-reactive immunoglobulin M (IgM) molecule. Hypothetically, this molecule obtains its complementarity from the first step of protein glycosylations, initiated by GalNAc via reversible O-linkages to peptides displaying Ser/Thr motifs, whereas the subsequent transferase depletion completes germ cell maturation and cell renewal, associated with loss of glycosidic bonds and release of O-glycan-depleted proteins, such as complementary IgM revealing the structure of the volatilely expressed "lost" glycan carrier through germline Ser residues. Consequently, the evolutionary/developmental first glycosylations of proteins appear metabolically related or identical to that of the mucin-type, potentially "aberrant" monosaccharide GalNAcα1-O-Ser/Thr-R, also referred to as the Tn (T "nouvelle") antigen, and explain the anti-Tn cross-reactivity of human innate or "natural" anti-A-specific isoagglutinin and the pronounced occurrence of cross-reactive anti-Tn antibody in plasma from humans with histo-blood group O. In fact, A-allelic, phenotype-specific GalNAc glycosylation of plasma proteins does not occur in human blood group O, affecting anti-Tn antibody levels, which may function as a growth regulator that contributes to a potential survival advantage of this group in the overall risk of developing cancer when compared with non-O blood groups.

Lack of species-specific difference in pulmonary function when using mouse versus human plasma in a mouse model of hemorrhagic shock

BACKGROUND

Clinical studies have demonstrated that the early and empiric use of plasma improves survival after hemorrhagic shock. We have demonstrated in rodent models of hemorrhagic shock that resuscitation with plasma is protective to the lungs compared with lactated Ringer's solution. As our long-term objective is to determine the molecular mechanisms that modulate plasma's protective effects in injured bleeding patients, we have used human plasma in a mouse model of hemorrhagic shock. The goal of the current experiments is to determine if there are significant adverse effects on lung injury when using human versus mouse plasma in an established murine model of hemorrhagic shock and laparotomy.

METHODS

Mice underwent laparotomy and 90 minutes of hemorrhagic shock to a mean arterial pressure (MAP) of 35 ± 5 mm Hg followed by resuscitation at 1× shed blood using either mouse fresh frozen plasma (FFP), human FFP, or human lyophilized plasma. Mean arterial pressure was recorded during shock and for the first 30 minutes of resuscitation. After 3 hours, animals were killed, and lungs collected for analysis.

RESULTS

There was a significant increase in early MAP when mouse FFP was used to resuscitate animals compared with human FFP or human lyophilized plasma. However, despite these differences, analysis of the mouse lungs revealed no significant differences in pulmonary histopathology, lung permeability, or lung edema between all three plasma groups. Analysis of neutrophil infiltration in the lungs revealed that mouse FFP decreased neutrophil influx as measured by neutrophil staining; however, myeloperoxidase immunostaining revealed no significant differences in between groups.

CONCLUSION

The study of human plasma in a mouse model of hemorrhagic shock is feasible but does reveal some differences compared with mouse plasma-based resuscitation in physiologic measures such as MAP postresuscitation. Measures of end organ function such as lung injury appear to be comparable in this acute model of hemorrhagic shock and resuscitation.

Crosstalk between ABO and Forssman (FORS) blood group systems: FORS1 antigen synthesis by ABO gene-encoded glycosyltransferases

A and B alleles at the ABO genetic locus specify A and B glycosyltransferases that catalyze the biosynthesis of A and B oligosaccharide antigens, respectively, of blood group ABO system which is important in transfusion and transplantation medicine. GBGT1 gene encodes Forssman glycolipid synthase (FS), another glycosyltransferase that produces Forssman antigen (FORS1). Humans are considered to be Forssman antigen-negative species without functional FS. However, rare individuals exhibiting Apae phenotype carry a dominant active GBGT1 gene and express Forssman antigen on RBCs. Accordingly, FORS system was recognized as the 31st blood group system. Mouse ABO gene encodes a cis-AB transferase capable of producing both A and B antigens. This murine enzyme contains the same GlyGlyAla tripeptide sequence as FSs at the position important for the determination of sugar specificity. We, therefore, transfected the expression construct into appropriate recipient cells and examined whether mouse cis-AB transferase may also exhibit FS activity. The result was positive, confirming the crosstalk between the ABO and FORS systems. Further experiments have revealed that the introduction of this tripeptide sequence to human A transferase conferred some, although weak, FS activity, suggesting that it is also involved in the recognition/binding of acceptor substrates, in addition to donor nucleotide-sugars.

ABO Blood-group Antigens in Oral Cancer

Tumor progression is often associated with altered glycosylation of the cell-surface proteins and lipids. The peripheral part of these cell-surface glycoconjugates often carries carbohydrate structures related to the ABO and Lewis blood-group antigens. The expression of histo-blood-group antigens in normal human tissues is dependent on the type of differentiation of the epithelium. In most human carcinomas, including oral carcinoma, a significant event is decreased expression of histo-blood-group antigens A and B. The mechanisms of aberrant expression of blood-group antigens are not clear in all cases. A relative down-regulation of the glycosyltransferase that is involved in the biosynthesis of A and B antigens is seen in oral carcinomas in association with tumor development. The events leading to loss of A transferase activity are related, in some instances, to loss of heterozygosity (LOH) involving chromosome 9q34, which is the locus for the ABO gene, and in other cases, to a hypermethylation of the ABO gene promoter. The fact that hypermethylation targets the ABO locus, but not surrounding genes, suggests that the hypermethylation is a specific tumor-related event. However, since not all situations with lack of expression of A/B antigens can be explained by LOH or hypermethylation, other regulatory factors outside the ABO promoter may be functional in transcriptional regulation of the ABO gene. Altered blood group antigens in malignant oral tissues may indicate increased cell migration. This hypothesis is supported by studies showing that normal migrating oral epithelial cells like malignant cells show lack of expression of A/B antigens, and by studies that target ABH antigens to key receptors controlling adhesion and motility, such as integrins, cadherins, and CD-44.

Novel UDP-GalNAc Derivative Structures Provide Insight into the Donor Specificity of Human Blood Group Glycosyltransferase

Two closely related glycosyltransferases are responsible for the final step of the biosynthesis of ABO(H) human blood group A and B antigens. The two enzymes differ by only four amino acid residues, which determine whether the enzymes transfer GalNAc from UDP-GalNAc or Gal from UDP-Gal to the H-antigen acceptor. The enzymes belong to the class of GT-A folded enzymes, grouped as GT6 in the CAZy database, and are characterized by a single domain with a metal dependent retaining reaction mechanism. However, the exact role of the four amino acid residues in the specificity of the enzymes is still unresolved. In this study, we report the first structural information of a dual specificity cis-AB blood group glycosyltransferase in complex with a synthetic UDP-GalNAc derivative. Interestingly, the GalNAc moiety adopts an unusual yet catalytically productive conformation in the binding pocket, which is different from the "tucked under" conformation previously observed for the UDP-Gal donor. In addition, we show that this UDP-GalNAc derivative in complex with the H-antigen acceptor provokes the same unusual binding pocket closure as seen for the corresponding UDP-Gal derivative. Despite this, the two derivatives show vastly different kinetic properties. Our results provide a important structural insight into the donor substrate specificity and utilization in blood group biosynthesis, which can very likely be exploited for the development of new glycosyltransferase inhibitors and probes.

High Resolution Structures of the Human ABO(H) Blood Group Enzymes in Complex with Donor Analogs Reveal That the Enzymes Utilize Multiple Donor Conformations to Bind Substrates in a Stepwise Manner

Homologous glycosyltransferases α-(1→3)-N-acetylgalactosaminyltransferase (GTA) and α-(1→3)-galactosyltransferase (GTB) catalyze the final step in ABO(H) blood group A and B antigen synthesis through sugar transfer from activated donor to the H antigen acceptor. These enzymes have a GT-A fold type with characteristic mobile polypeptide loops that cover the active site upon substrate binding and, despite intense investigation, many aspects of substrate specificity and catalysis remain unclear. The structures of GTA, GTB, and their chimeras have been determined to between 1.55 and 1.39 Å resolution in complex with natural donors UDP-Gal, UDP-Glc and, in an attempt to overcome one of the common problems associated with three-dimensional studies, the non-hydrolyzable donor analog UDP-phosphono-galactose (UDP-C-Gal). Whereas the uracil moieties of the donors are observed to maintain a constant location, the sugar moieties lie in four distinct conformations, varying from extended to the "tucked under" conformation associated with catalysis, each stabilized by different hydrogen bonding partners with the enzyme. Further, several structures show clear evidence that the donor sugar is disordered over two of the observed conformations and so provide evidence for stepwise insertion into the active site. Although the natural donors can both assume the tucked under conformation in complex with enzyme, UDP-C-Gal cannot. Whereas UDP-C-Gal was designed to be "isosteric" with natural donor, the small differences in structure imposed by changing the epimeric oxygen atom to carbon appear to render the enzyme incapable of binding the analog in the active conformation and so preclude its use as a substrate mimic in GTA and GTB.

Strategies to overcome the ABO barrier in kidney transplantation

Kidney transplantation across the ABO blood group barrier was long considered a contraindication for transplantation, but in an effort to increase donor pools, specific regimens for ABO-incompatible (ABOi) transplantation have been developed. These regimens are now widely used as an integral part of the available treatment options. Various desensitization protocols, commonly based on transient depletion of preformed anti-A and/or anti-B antibodies and modulation of B-cell immunity, enable excellent transplant outcomes, even in the long-term. Nevertheless, the molecular mechanisms behind transplant acceptance facilitated by a short course of anti-humoral treatment are still incompletely understood. With the evolution of efficient clinical programmes, tailoring of recipient preconditioning based on individual donor-recipient blood type combinations and the levels of pretransplant anti-A/B antibodies has become possible. In the context of low antibody titres and/or donor A2 phenotype, immunomodulation and/or apheresis might be dispensable. A concern still exists, however, that ABOi kidney transplantation is associated with an increased risk of surgical and infectious complications, partly owing to the effects of extracorporeal treatment and intensified immunosuppression. Nevertheless, a continuous improvement in desensitization strategies, with the aim of minimizing the immunosuppressive burden, might pave the way to clinical outcomes that are comparable to those achieved in ABO-compatible transplantation.

No evidence for a direct effect of von Willebrand factor's ABH blood group antigens on von Willebrand factor clearance

BACKGROUND

One of the major determinants of von Willebrand factor (VWF) plasma levels is ABO blood group status, and individuals with blood group O have ~ 25% lower plasma levels. The exact mechanism behind this relationship remains unknown, although effects on clearance have been postulated.

OBJECTIVES

To determine whether clearance of VWF is directly dependent on the presence of ABH antigens on VWF.

METHODS

Three type 3 von Willebrand disease (VWD) patients were infused with Haemate-P, and the relative loading of VWF with ABH antigens at different time points was measured. VWF-deficient mice were injected with purified plasma-derived human VWF obtained from donors with either blood group A, blood group B, or blood group O.

RESULTS

In mice, we found no difference in clearance rate between plasma-derived blood group A, blood group B and blood group O VWF. Faster clearance of the blood group O VWF present in Haemate-P infused in type 3 VWD patients would have resulted in a relative increase in the loading of VWF with A and B antigens over time. However, we observed a two-fold decrease in the loading with A and B antigens in two out of three patients, and stable loading in the third patient.

CONCLUSION

There is no direct effect of ABH antigens on VWF in VWF clearance. We demonstrate that, in a direct comparison within one individual, blood group O VWF is not cleared faster than blood group A or blood group B VWF. Clearance differences between blood group O and non-blood group O individuals may therefore be related to the blood group status of the individual rather than the ABH antigen loading on VWF itself.

An integrative evolution theory of histo-blood group ABO and related genes

The ABO system is one of the most important blood group systems in transfusion/transplantation medicine. However, the evolutionary significance of the ABO gene and its polymorphism remained unknown. We took an integrative approach to gain insights into the significance of the evolutionary process of ABO genes, including those related not only phylogenetically but also functionally. We experimentally created a code table correlating amino acid sequence motifs of the ABO gene-encoded glycosyltransferases with GalNAc (A)/galactose (B) specificity, and assigned A/B specificity to individual ABO genes from various species thus going beyond the simple sequence comparison. Together with genome information and phylogenetic analyses, this assignment revealed early appearance of A and B gene sequences in evolution and potentially non-allelic presence of both gene sequences in some animal species. We argue: Evolution may have suppressed the establishment of two independent, functional A and B genes in most vertebrates and promoted A/B conversion through amino acid substitutions and/or recombination; A/B allelism should have existed in common ancestors of primates; and bacterial ABO genes evolved through horizontal and vertical gene transmission into 2 separate groups encoding glycosyltransferases with distinct sugar specificities.

Structures of a human blood group glycosyltransferase in complex with a photo-activatable UDP-Gal derivative reveal two different binding conformations

Glycosyltransferases (GTs) catalyse the sequential addition of monosaccharides to specific acceptor molecules and play major roles in key biological processes. GTs are classified into two main families depending on the inverted or retained stereochemistry of the glycosidic bond formed during the reaction. While the mechanism of inverting enzymes is well characterized, the precise nature of retaining GTs is still a matter of much debate. In an attempt to clarify this issue, studies were initiated to identify reaction-intermediate states by using a crystallographic approach based on caged substrates. In this paper, two distinct structures of AA(Gly)B, a dual-specificity blood group synthase, are described in complex with a UDP-galactose derivative in which the O6'' atom is protected by a 2-nitrobenzyl group. The distinct conformations of the caged substrate in both structures of the enzyme illustrate the highly dynamic nature of its active site. An attempt was also made to photolyse the caged compound at low temperature, which unfortunately is not possible without damaging the uracil group as well. These results pave the way for kinetic crystallography experiments aiming at trapping and characterizing reaction-intermediate states in the mechanism of enzymatic glycosyl transfer.

Complementary innate (anti-A-specific) IgM emerging from ontogenic O-GalNAc-transferase depletion: (Innate IgM complementarity residing in ancestral antigen completeness)

The murine and the human genome have global properties in common. So the murine anti-A-specific complementary IgM and related human innate isoagglutinin represent developmental, 2-mercaptoethanol-sensitive, complement-binding glycoproteins, which do not arise from any measurable environmentally-induced or auto- immune response. The murine anti-A certainly originates from a cell surface- or cell adhesion molecule, which in the course of germ cell development becomes devoid of O-GalNAc-transferase and is released into the circulation. In human sera the enzyme occurs exclusively in those of blood group A- and AB subjects, while in group O(H) an identically encoded protein lets expect an opposite function and appears in conjunction with a complementary anti-A reactive glycoprotein. Since O-glycosylations rule the carbohydrate metabolism in growth and reproduction processes, we propose that the ancestral histo-(blood)-group A molecule arises in the course of O-GalNAc-glycosylations of glycolipids and protein envelops at progenitor cell surfaces. Germ cell development postulates embryonic stem cell fidelity, which is characterised by persistent production of α-linked O-GalNAc-glycans. They are determined by the A-allele within the human, "complete" histo (blood) group AB(O) structure that in early ontogeny is hypothesised to be synthesised independently from the final phenotype. The structure either passes "completely" through the germline, in transferase-secreting mature tissues becoming the "complete" phenotype AB, or disappears in exhaustive glycotransferase depletion from the differentiating cell surfaces and leaves behind the "incomplete" blood group O-phenotype, which has released a transferase- and O-glycan-depleted, complementary glycoprotein (IgM) into the circulation. The process implies, that in humans the different blood phenotypes evolve from a "complete" AB(O) molecular complex in a distinct enzymatic and/or complement cascade suggesting O-glycanase involvements. While the murine and human oocyte zona pellucida express identical O-glycans, the human phenotype O might be explainable by the kinetics of the murine ovarian O-GalNAc glycan synthesis and the complementary anti-A released in parallel. The maturing murine ovary may provide insight into encoding of the physiologically superior α-linked GalNAc ancestral epitope that becomes essential in reproduction as well as in tissue renewal events. According to recent reports, O-GalNAc-transferase-determined blood group A suggests superiority in human female fertility and was called even "protective". So the minor fertility of blood-group-O females may reside in a critical timing in developmental shifting of enzyme functions affecting the formation of GalNAc-determined hormone receptors on the way to maturation. Experiments that had inserted an oocyte genome into a somatic one to generate pluripotent stem cells, might elucidate a developmental dilemma by testing oocytes from different blood group AB donors donors. Perhaps they will unmask the molecular basis of an evolutionary trend, while stem cell generation itself capitalises on the enzymatically-advantaged, lineage-maintaining (histo) blood group A-allele, which guaranties ancestral functional completeness.

Ancestry runs deeper than blood: the evolutionary history of ABO points to cryptic variation of functional importance

The ABO histo-blood group, first discovered over a century ago, is found not only in humans but also in many other primate species, with the same genetic variants maintained for at least 20 million years. Polymorphisms in ABO have been associated with susceptibility to a large number of human diseases, from gastric cancers to immune or artery diseases, but the adaptive phenotypes to which the polymorphism contributes remain unclear. We suggest that variation in ABO has been maintained by frequency-dependent or fluctuating selection pressures, potentially arising from co-evolution with gut pathogens. We further hypothesize that the histo-blood group labels A, B, AB, and O do not offer a full description of variants maintained by natural selection, implying that there are unrecognized, functionally important, antigens beyond the ABO group in humans and other primates.

Base-modified donor analogues reveal novel dynamic features of a glycosyltransferase

Glycosyltransferases (GTs) are enzymes that are involved, as Nature's "glycosylation reagents," in many fundamental biological processes including cell adhesion and blood group biosynthesis. Although of similar importance to that of other large enzyme families such as protein kinases and proteases, the undisputed potential of GTs for chemical biology and drug discovery has remained largely unrealized to date. This is due, at least in part, to a relative lack of GT inhibitors and tool compounds for structural, mechanistic, and cellular studies. In this study, we have used a novel class of GT donor analogues to obtain new structural and enzymological information for a representative blood group GT. These analogues interfere with the folding of an internal loop and the C terminus, which are essential for catalysis. Our experiments have led to the discovery of an entirely new active site folding mode for this enzyme family, which can be targeted in inhibitor development, similar to the DFG motif in protein kinases. Taken together, our results provide new insights into substrate binding, dynamics, and utilization in this important enzyme family, which can very likely be harnessed for the rational development of new GT inhibitors and probes.

Allograft outcomes in outbred mice

Inbreeding depression and lack of genetic diversity in inbred mice could mask unappreciated causes of graft failure or remove barriers to tolerance induction. To test these possibilities, we performed heart transplantation between outbred or inbred mice. Unlike untreated inbred mice in which all allografts were rejected acutely (6-16 days posttransplantation), untreated outbred mice had heterogeneous outcomes, with grafts failing early (<4 days posttransplantation), acutely (6-24 days) or undergoing chronic rejection (>75 days). Blocking T cell costimulation induced long-term graft acceptance in both inbred and outbred mice, but did not prevent the early graft failure observed in the latter. Further investigation of this early phenotype established that it is dependent on the donor, and not the recipient, being outbred and that it is characterized by hemorrhagic necrosis and neutrophilic vasculitis in the graft without preformed, high titer antidonor antibodies in the recipient. Complement or neutrophil depletion prevented early failure of outbred grafts, whereas transplanting CD73-deficient inbred hearts, which are highly susceptible to ischemia-reperfusion injury, recapitulated the early phenotype. Therefore, outbred mice could provide broader insight into donor and recipient determinants of allograft outcomes but their hybrid vigor and genetic diversity do not constitute a uniform barrier to tolerance induction.

ABO blood groups influence macrophage-mediated phagocytosis of Plasmodium falciparum-infected erythrocytes

Erythrocyte polymorphisms associated with a survival advantage to Plasmodium falciparum infection have undergone positive selection. There is a predominance of blood group O in malaria-endemic regions, and several lines of evidence suggest that ABO blood groups may influence the outcome of P. falciparum infection. Based on the hypothesis that enhanced innate clearance of infected polymorphic erythrocytes is associated with protection from severe malaria, we investigated whether P. falciparum-infected O erythrocytes are more efficiently cleared by macrophages than infected A and B erythrocytes. We show that human macrophages in vitro and mouse monocytes in vivo phagocytose P. falciparum-infected O erythrocytes more avidly than infected A and B erythrocytes and that uptake is associated with increased hemichrome deposition and high molecular weight band 3 aggregates in infected O erythrocytes. Using infected A₁, A₂, and O erythrocytes, we demonstrate an inverse association of phagocytic capacity with the amount of A antigen on the surface of infected erythrocytes. Finally, we report that enzymatic conversion of B erythrocytes to type as O before infection significantly enhances their uptake by macrophages to observed level comparable to that with infected O wild-type erythrocytes. These data provide the first evidence that ABO blood group antigens influence macrophage clearance of P. falciparum-infected erythrocytes and suggest an additional mechanism by which blood group O may confer resistance to severe malaria.

Plasmodium falciparum malaria is considered to be one of the strongest forces for evolutionary selection pressure on the human genome. Different red blood cell variants associated with a survival advantage to P. falciparum infection have undergone positive selection. Blood group O is found more frequently in malaria-endemic regions and has been associated with protection against severe malaria and death. However the biological basis of protection remains unclear. In this study, we investigated innate immune clearance of P. falciparum-infected erythrocytes by macrophages as a possible mode of protection. We show that macrophages clear P. falciparum-infected O erythrocytes more avidly than infected A and B erythrocytes. We also report that enzymatic conversion of infected blood group B red cells to type as “O” like erythrocytes significantly enhances their uptake by macrophages to a level comparable to that observed with infected O wild type erythrocytes. These data provide the first evidence that clearance of P. falciparum-infected erythrocytes is influenced by human ABO blood groups and suggest a new mechanism by which blood group O may contribute to protection against severe malaria.

Genetic basis of atherosclerosis: insights from mice and humans

Atherosclerosis is a complex and heritable disease involving multiple cell types and the interactions of many different molecular pathways. The genetic and molecular mechanisms of atherosclerosis have, in part, been elucidated by mouse models; at least 100 different genes have been shown to influence atherosclerosis in mice. Importantly, unbiased genome-wide association studies have recently identified a number of novel loci robustly associated with atherosclerotic coronary artery disease. Here, we review the genetic data elucidated from mouse models of atherosclerosis, as well as significant associations for human coronary artery disease. Furthermore, we discuss in greater detail some of these novel human coronary artery disease loci. The combination of mouse and human genetics has the potential to identify and validate novel genes that influence atherosclerosis, some of which may be candidates for new therapeutic approaches.

ABO research in the modern era of genomics

Research on ABO has advanced significantly in recent years. A database was established to manage the sequence information of an increasing number of novel alleles. Genome sequencings have identified ABO orthologues and paralogues in various organisms and enhanced the knowledge on the evolution of the ABO and related genes. The most prominent advancements include clarification of the association between ABO and different disease processes. For instance, ABO status affects the infectivity of certain strains of Helicobacter pylori and Noroviruses as well as the sequestration and rosetting of red blood cells infected with Plasmodium falciparum. Genome-wide association studies have conclusively linked the ABO locus to pancreatic cancer, venous thromboembolism, and myocardial infarction in the presence of coronary atherosclerosis. These findings suggest ABO's important role in determining an individual's susceptibility to such diseases. Furthermore, our understanding of the structures of A and B transferases and their enzymology has been dramatically improved. ABO has also become a research subject in neurobiology and the preparation of artificial/universal blood and became a topic in the pseudoscience of "blood type diets." With such new progress, it has become evident that ABO is a critical player in the modern era of genomic medicine. This article provides the most up-to-date information regarding ABO genomics.

"Natural" antibodies and histo-blood groups in biological development with respect to histo-blood group A. A perspective review

The "inappropriate" A-specific ovarian glycosphingolipids discovered in unfertilized C57BL/10J female mice reflect growth processes, which suggest the activity of embryonic stem cells undergoing genetic polymorphism. And the responding anti-GalNAc antibody represents the first classical "natural" antibody, which was unmasked as a highly specific autoantibody. This murine anti-A is subspecifically distinct from the human antibody, discovering by a broader reactivity growth-dependent, xenoreactive A-specific structures also in non-reproductive murine tissues, where an equivalent of the human AB gene family as a cis AB-gene encodes A-and B glycotransferases. Expression of antigen is known to need always more than its encoded enzyme, and the special mechanism which in the C57BL/10J murine ovarian glycospingolipids blocks the expression of "B" still remains still unknown. A herewith arising postulation of a growth-predominating common biological activity may be supported by findings in rats. The number of A-genes here significantly exceeds those of B and in the Wistar rat the A-antigen is only expressed in the wild type, while B-expression requires the transfer of human B. Nevertheless in transgenic rats, the appearance of "A" still remains more pronounced. The observations lead to reports on animals, which do not show AB transferase production or a respective antigen expression in their normal tissues, but inconcistently display A activity in malignant tumors. And respective examples are delivered by phenotype independent neo expressions of "inappropriate" A-specific structures in human cancer. Although in comparison with epitope deletions they are rare, the ubiquitous "natural" (IgM and IgG) anti-A and anti-B levels, against self and not self, irrespective of the blood group in any normal human sera, may reflect invisible "inappropriate" A-specific growth. The role of the associated (auto) anti-B might be different, because B-neo expressions obviously not occur in cancer, and anti-gal-antibodies are supposed to originate primarily from environmental, cross-reactive stimulation, and beyond their functions in defense are otherwise engaged in physiology. In general natural antibody specificities undergo significant phylogenetical changes within the species. However, the in nature wide-spread "natural" anti-A agglutinin specificities survived or even predominated the long-term evolution from the brown trout up to man and still respond to the biological power, i.e. the products of a CAZY glycosyltransferase 6 (ABO) gene family. It is so hypothesized that both, the murine and human "natural" anti-A antibodies represent examples of a still to be analyzed polyclonal response to a provocative, species-independent evolutionary epitope, which arises or escapes by some enzymatic predominance from the genetical polymorphism in a consistent developmental process.

A novel method for ABO genotyping using a DNA chip

ABO genotyping is often performed to identify the blood type of decomposed samples, which is difficult to be determined by a serological test. In this study, we developed a simple method for ABO genotyping using a DNA chip. In this method, polymerase chain reaction-amplified and fluorescent-labeled fragments in the ABO gene and primate-specific D17Z1 were hybridized with DNA probes on a chip designed to detect single nucleotide polymorphisms (SNPs) in the ABO gene and part of the D17Z1 sequence. Using blood samples from 42 volunteers and 10 animal species, we investigated whether the chip could be used to detect SNPs in the ABO gene and the D17Z1 sequence. This method was then applied to various forensic samples, and it was confirmed that this method was suitable for the simultaneous analyses of ABO genotyping and species identification. This method fulfills the recent need for the development of rapid and convenient methods for criminal investigations.

Induction of human blood group a antigen expression on mouse cells, using lentiviral gene transduction

The ABO histo-blood group system is the most important antigen system in transplantation medicine, yet no small animal model of the ABO system exists. To determine the feasibility of developing a murine model, we previously subcloned the human alpha-1,2-fucosyltransferase (H-transferase, EC 2.4.1.69) cDNA and the human alpha-1,3-N-acetylgalactosaminyltransferase (A-transferase, EC 2.4.1.40) cDNA into lentiviral vectors to study their ability to induce human histo-blood group A antigen expression on mouse cells. Herein we investigated the optimal conditions for human A and H antigen expression in murine cells. We determined that transduction of a bicistronic lentiviral vector (LvEF1-AH-trs) resulted in the expression of A antigen in a mouse endothelial cell line. We also studied the in vivo utility of this vector to induce human A antigen expression in mouse liver. After intrahepatic injection of LvEF1-AH-trs, A antigen expression was observed on hepatocytes as detected by immunohistochemistry and real-time RT-PCR. In human group A erythrocyte-sensitized mice, A antigen expression in the liver was associated with tissue damage, and deposition of antibody and complement. These results suggest that this gene transfer strategy can be used to simulate the human ABO blood group system in a murine model. This model will facilitate progress in the development of interventions for ABO-incompatible transplantation and transfusion scenarios, which are difficult to develop in clinical or large animal settings.

Generation of histo-blood group B transferase by replacing the N-acetyl-D-galactosamine recognition domain of human A transferase with the galactose-recognition domain of evolutionarily related murine alpha1,3-galactosyltransferase

BACKGROUND

The alpha1,3-galactosyl epitope (alpha1-3Gal epitope), a major xenotransplant antigen, is synthesized by alpha1,3-galactosyltransferase (alpha1-3Gal transferase), which is evolutionarily related to the histo-blood group A/B transferases.

STUDY DESIGN AND METHODS

We constructed structural chimeras between the human type A and murine alpha1-3Gal transferases and examined their activity and specificity.

RESULTS

In many instances, a total loss of transferase activity was observed. Certain areas could be exchanged, with a potential diminishing of activity. With a few constructs, changes in acceptor substrate specificity were suspected. Unexpectedly, a functional conversion from A to B transferase activity was observed after replacing the short sequence of human A transferase with the corresponding sequence from murine alpha1-3Gal transferase.

CONCLUSION

Because these two paralogous enzymes differ in 16 positions of the 38 amino acid residues in the replaced region, our finding may suggest that despite separate evolution and diversified acceptors, these glycosyltransferases still share the three-dimensional domain structure that is responsible for their sugar specificity, arguing against the functional requirement of a strong purifying selection playing a role in the evolution of the ABO family of genes.

Mosaic genealogy of the Mus musculus genome revealed by 21 nuclear genes from its three subspecies

Patterns of genetic variation provide insight into the evolutionary history of a species. Mouse (Mus musculus) is a good model for this purpose. Here we present the analysis of genealogies of the 21 nuclear loci and one mitochondrial DNA region in M. musculus based on our nucleotide sequences of nine inbred strains from three M. musculus subspecies (musculus, domesticus, and castaneus) and one M. spicilegus strain as an outgroup. The mitochondrial DNA gene genealogy of those strains confirmed the introgression pattern of one musculus strain. When all the nuclear DNA data were concatenated to produce a phylogenetic tree of nine strains, musculus and domesticus strains formed monophyletic clusters with each other, while the two castaneus strains were paraphyletic. When each DNA region was treated independently, the phylogenetic networks revealed an unnegligibly high level of subspecies admixture and the mosaic nature of their genome. Estimation of ancestral and derived population sizes and migration rates suggests the effects of ancestral polymorphism and gene flow on the pattern of genetic variation of the current subspecies. Gene genealogies of Fut4 and Dfy loci also suggested existence of the gene flow between M. musculus and M. spicilegus or other distant species.

Regulation of glycan structures in animal tissues: transcript profiling of glycan-related genes

Glycan structures covalently attached to proteins and lipids play numerous roles in mammalian cells, including protein folding, targeting, recognition, and adhesion at the molecular or cellular level. Regulating the abundance of glycan structures on cellular glycoproteins and glycolipids is a complex process that depends on numerous factors. Most models for glycan regulation hypothesize that transcriptional control of the enzymes involved in glycan synthesis, modification, and catabolism determines glycan abundance and diversity. However, few broad-based studies have examined correlations between glycan structures and transcripts encoding the relevant biosynthetic and catabolic enzymes. Low transcript abundance for many glycan-related genes has hampered broad-based transcript profiling for comparison with glycan structural data. In an effort to facilitate comparison with glycan structural data and to identify the molecular basis of alterations in glycan structures, we have developed a medium-throughput quantitative real time reverse transcriptase-PCR platform for the analysis of transcripts encoding glycan-related enzymes and proteins in mouse tissues and cells. The method employs a comprehensive list of >700 genes, including enzymes involved in sugar-nucleotide biosynthesis, transporters, glycan extension, modification, recognition, catabolism, and numerous glycosylated core proteins. Comparison with parallel microarray analyses indicates a significantly greater sensitivity and dynamic range for our quantitative real time reverse transcriptase-PCR approach, particularly for the numerous low abundance glycan-related enzymes. Mapping of the genes and transcript levels to their respective biosynthetic pathway steps allowed a comparison with glycan structural data and provides support for a model where many, but not all, changes in glycan abundance result from alterations in transcript expression of corresponding biosynthetic enzymes.

Genetic regulation of plasma von Willebrand factor levels: quantitative trait loci analysis in a mouse model

BACKGROUND

The genetic factors responsible for the wide variation in plasma von Willebrand factor (VWF) levels observed among individuals are largely unknown, although these genes are also likely to contribute to variability in the severity of von Willebrand disease (VWD) and other bleeding and thrombotic disorders. We have previously mapped two genes contributing to the regulation of plasma VWF levels in mice (Mvwf1 on chromosome 11 and Mvwf2 on chromosome 6).

OBJECTIVE

To identify additional quantitative trait loci (QTL) contributing to the genetic regulation of murine plasma VWF levels.

METHODS

To map genetic loci contributing to the > 7-fold difference in plasma VWF levels between two mouse strains (A/J and CASA/RkJ), high-density individual genotyping and R/qtl analyses were applied to a previously generated set of approximately 200 F2 mice obtained from an intercross of these two inbred lines.

RESULTS

Genomic loci for two additional candidate VWF modifier genes were identified: Mvwf3 on chromosome 4 and Mvwf4 on chromosome 13. These loci demonstrate primarily epistatic effects when co-inherited with two CASA/RkJ Vwf alleles, although Mvwf4 may also exert a small, independent, additive effect.

CONCLUSIONS

Mvwf3 and Mvwf4, combined with the effect of Mvwf2, explain approximately 45% of the genetic variation in plasma VWF level among the A/J and CASA/RkJ strains. Mvwf3 and Mvwf4 exhibit homology of synteny to three human chromosomal segments (on chromosomes 1, 5 and 6) previously reported by the Genetic Analysis of Idiopathic Thrombophilia (GAIT) study, suggesting that orthologs of Mvwf3 and Mvwf4 may also encode important VWF modifier genes in humans.

Impairment of thymocyte development by dominant-negative Kuzbanian (ADAM-10) is rescued by the Notch ligand, delta-1

Although Notch plays a crucial role in T cell development, regulation of Notch signaling in the thymus is not well understood. Kuzbanian, an ADAM protease, has been implicated in the cleavage of both Notch receptors and the Notch ligand, Delta. In this study we show that the expression of a dominant-negative form of Kuzbanian (dnKuz) leads to reduced TCRbeta expression in double-negative thymocytes and to a partial block between the double-negative to double-positive stages of development. These defects were rescued by overexpression of Delta-1 on thymocytes. Mixed chimeras showed a cell-autonomous block by dnKuz, but non-cell-autonomous rescue by Delta-1. This suggests that dnKuz impairs Notch signaling in receiving cells, and increasing Delta-1 on sending cells overcomes this defect. Interestingly, the expression of an activated form of Notch-1 rescued some, but not all, the defects in dnKuz Tg mice. Our data suggest that multiple Notch-dependent steps in early thymocyte development require Kuzbanian, but differ in the involvement of other Notch signaling components.

Mice are unsuitable for modelling ABO discordance despite strain-specific A cross-reactive natural IgM

ABO blood group antigens are immunodominant cell surface oligosaccharides. The function of the ABO system is clinically important in blood transfusion and solid organ transplantation but there is no small animal model of ABO discordance. The present study demonstrated A glycoconjugate-reactive IgM in the serum of CBA/Ca mice by enzyme-linked immunosorbent assay but showed with sugar blocking that the specificity of this IgM was different from that of human anti-A IgM. Furthermore, immunisation of CBA/Ca mice with the A antigen did not increase reactive IgM titre. In contrast, knock-out mice for the related carbohydrate antigen galactose(alpha1,3)galactose mounted a serum IgM response when immunised with the non-self galactose(alpha1,3)galactose antigen, which was shown to be T cell-dependent using a nude/knock-out animal. Reverse transcription-polymerase chain reaction identified transcripts for the enzyme likely to be responsible for the synthesis of the A antigen in organs from CBA/Ca mice although the A antigen was not detected in the same organs by immunohistochemistry. We conclude that CBA/Ca mice possess natural serum IgM with different characteristics to human anti-A IgM and that CBA/Ca mice may also express the A antigen. As a result, these mice are not suitable for use as a small animal model of ABO discordance.