Contribution of gene conversion to the retention of the sequence for M blood group type determinant in glycophorin E gene

A Comprehensive Review of Our Current Understanding of Red Blood Cell (RBC) Glycoproteins

Human red blood cells (RBC), which are the cells most commonly used in the study of biological membranes, have some glycoproteins in their cell membrane. These membrane proteins are band 3 and glycophorins A-D, and some substoichiometric glycoproteins (e.g., CD44, CD47, Lu, Kell, Duffy). The oligosaccharide that band 3 contains has one N-linked oligosaccharide, and glycophorins possess mostly O-linked oligosaccharides. The end of the O-linked oligosaccharide is linked to sialic acid. In humans, this sialic acid is N-acetylneuraminic acid (NeuAc). Another sialic acid, N-glycolylneuraminic acid (NeuGc) is present in red blood cells of non-human origin. While the biological function of band 3 is well known as an anion exchanger, it has been suggested that the oligosaccharide of band 3 does not affect the anion transport function. Although band 3 has been studied in detail, the physiological functions of glycophorins remain unclear. This review mainly describes the sialo-oligosaccharide structures of band 3 and glycophorins, followed by a discussion of the physiological functions that have been reported in the literature to date. Moreover, other glycoproteins in red blood cell membranes of non-human origin are described, and the physiological function of glycophorin in carp red blood cell membranes is discussed with respect to its bacteriostatic activity.

p73 plays a role in erythroid differentiation through GATA1 induction

The TP73 gene gives rise to transactivation domain-p73 isoforms (TAp73) as well as DeltaNp73 variants with a truncated N terminus. Although TAp73alpha and -beta proteins are capable of inducing cell cycle arrest, apoptosis, and differentiation, DeltaNp73 acts in many cell types as a dominant-negative repressor of p53 and TAp73. It has been proposed that p73 is involved in myeloid differentiation, and its altered expression is involved in leukemic degeneration. However, there is little evidence as to which p73 variants (TA or DeltaN) are expressed during differentiation and whether specific p73 isoforms have the capacity to induce, or hinder, this differentiation in leukemia cells. In this study we identify GATA1 as a direct transcriptional target of TAp73alpha. Furthermore, TAp73alpha induces GATA1 activity, and it is required for erythroid differentiation. Additionally, we describe a functional cooperation between TAp73 and DeltaNp73 in the context of erythroid differentiation in human myeloid cells, K562 and UT-7. Moreover, the impaired expression of GATA1 and other erythroid genes in the liver of p73KO embryos, together with the moderated anemia observed in p73KO young mice, suggests a physiological role for TP73 in erythropoiesis.

Molecular evolution of alleles of the glycophorin A gene

Highly-homologous Glycophorin A (GPA), B and E genes are triplicate genes, and involve many subtypes and minor antigens constructing the Miltenberger subsystem. These genes and most of the variants are hypothesized to arise by recombination, because hot spots are located in the gene sequences. By sequencing exons 1-7 and introns 1-3 of standard alleles of GPA gene, M and N alleles were classified into six variations: provisionally called MN*M101, M102, M201, M202, N101 and N102 in our previous study. Here we further investigated the sequences of introns 4-6 using GPA gene-specific primers and by DNA sequencing, and found eight, five and nine new nucleotide substitutions or deletions in introns 4, 5 and 6, respectively. Using the computer program PHYLIP 3.5, the phylogenetic trees were reconstructed. Phylogenetic analysis of the allele sequences revealed that M200s alleles arose from M101 after the separation of M101 and N101 and branched to M201 and M202 via the accumulation of point mutations. M102 and N102 alleles were estimated to generate via recombination between M101 and N101 occurred around the hot spot. The findings also suggested the existence of other GPA variants with normal antigenicity, and are quite useful in the forensic and anthropological fields.

An application of PCR-single strand conformation polymorphism to MN genotyping

A PCR-based genotyping of MN blood group system was investigated for DNA samples taken from a population of 409 northern Japanese. DNA fragment (257bp) including exon 2 of glycophorin A (GPA) gene, in which encodes the determinants of MN antigens, was specifically amplified. On the analysis of PCR-single-strand conformation polymorphism (PCR-SSCP) for M alleles, band patterns of M(G) and M(T) were easily discriminated each other. For N alleles, three band patterns were observed, and we tentatively named these alleles as N(1), N(2) and N(V). The N(1) allele appeared predominantly and N(2) had two base substitutions at 1st (C-->A) and 56th (C-->T) in exon 2 of N(1). The other N(V), which was detected from a pair of a mother and her child, possessed a single base substitution at 23rd (A-->G) in intron 2. The allele frequencies of M(G), M(T), N(1) and N(2) were 0.4450, 0.0978, 0.4303 and 0.0269, respectively. The polymorphism information content and the probability of paternity exclusion by this MN genotyping were estimated to be 0.5252 and 0.3219, respectively.

A novel St(a) glycophorin produced via gene conversion of pseudoexon III from glycophorin E to glycophorin A gene

Stone (St(a)) is a variant antigen carried on human erythrocyte MNSs glycophorins (GPSt(a)) that are genetically associated with splicing mutations in GPA genes or with hybrid formation between GPA and GPB genes. Here we identify the first and rare gene conversion event in which GPE, the third member of the family, recombined with GPA, giving rise to a GPA-E-A hybrid gene encoding the St(a) antigen. Western blot detected expression in the proband of both GPA and GPSt(a) on the plasma membrane. Southern blot showed a new restriction fragment from the GPSt(a) gene, indicating an altered exon III-intron 3 junction. Sequencing of RT-PCR products identified one full-length and two shortened glycophorin cDNAs. The shortened forms were derived from GPSt(a) lacking one (exon III) and two exons (exon III and IV), respectively. To define the molecular basis for exon skipping, the genomic region spanning exon III of the GPSt(a) gene was amplified and sequenced. This revealed transfer from GPE to GPA of a DNA segment containing the pseudoexon III and its silent donor splice site. Thus, the inactivation of GPA exon III by conversion of a silent GPE donor splice site portrays a new molecular mechanism for St(a) antigen expression in human erythrocytes.

The gene encoding the myeloid-related protein 14 (MRP14), a calcium-binding protein expressed in granulocytes and monocytes, contains a potent enhancer element in the first intron

Myeloid-related proteins 8 and 14 (MRP8 and MRP14) are two Ca2+-binding proteins of the S-100 family highly abundant in myelomonocytic cells. The expression is not only dependent on the developmental status of the cell but also on the inflammatory situation in the tissue. In order to identify regulatory elements responsible for the high expression of MRP14 in myeloid cells, reporter gene constructs have been transfected into HL-60 cells, Mono Mac 6 cells, and L132 cells. We demonstrated that a DNA element in the first intron (positions 153-361) enhances the transcriptional activity of the homologous promoter and of the heterologous herpes simplex virus thymidine kinase promoter up to 37-fold. To further identify the functional site, the region between positions 153 and 192 was analyzed functionally using the thymidine kinase promoter. The region increased the expression in the same magnitude as the complete intron. This enhancer is highly conserved in the human and murine MRP genes, indicative of its involvement in the transcription of MRPs. Protein binding to the region is demonstrated using EMSA, DNA cross-linking, Southwestern blotting, and affinity purification. Affinity purification confirms that four proteins bind to the enhancer element.

PCR-based genotyping of MNSs blood group: subtyping of M allele to MG and MT

PCR-based genotyping of MNSs blood group system was investigated in combination with restriction fragment length polymorphism (RFLP), single-stand conformation polymorphism (SSCP) and allele-specific PCR amplification (ASPA) techniques. M and N alleles are based on three nucleotide substitutions in exon 2 and one base change (G or T) in an intron of glycophorin A locus. The latter single base change was also found among M alleles analyzed in this study, so that M allele appeared to be subdivided into MG and MT. All three alleles, MG, MT and N were identified clearly by RFLP or SSCP analysis following a single amplification. S and s alleles are based on one nucleotide substitution in exon 3 of glycophorin B gene. Genotyping of Ss blood group system was also explored by PCR-SSCP or ASPA analysis, and problems in the methods were discussed.

Detailed physical mapping of the genes encoding glycophorins A, B and E, as revealed by P1 plasmids containing human genomic DNA

Human glycophorins A, B and E (GPA, GPB and GPE) are members of the glycophorin gene family encompassing a 330-kb genomic segment located on chromosome 4, band q31 [Onda et al., J. Biol. Chem., 269 (1994) 13013-13020]. This gene family was apparently generated by two successive duplications of an ancestral gene. One of the progenitor genes, resulting from the first duplication, directly evolved into the GPA gene. The other progenitor gene acquired a unique 3'-region sequence and was then duplicated to yield GPB and GPE. In order to obtain a more detailed understanding of how these different members of the gene family evolved, we isolated several P1 plasmid clones encoding GPA, GPB or GPE. The precise locations of exon 1 and the exon encoding the transmembrane (TM) domain in GPA, GPB and GPE were then determined by hybridization with specific probes after restricted DNA fragments were separated by pulsed-field gel electrophoresis. The results obtained showed that the distances between exon 1 and exon 2 are almost equal for GPA and GPB, whereas this distance is larger in GPE. In contrast, the distance between exon 2 and the exon encoding the TM domain was shown to be the same among GPA, GPB and GPE. These results suggest that the gene divergence, i.e., insertions or deletions, took place after two successive duplications and supports the hypothesis that GPE acquired a portion of the GPA sequence surrounding exon 2 by gene conversion.