Identification of a novel A4GALT exon reveals the genetic basis of the P1/P2 histo-blood groups.
The A4GALT locus encodes a glycosyltransferase that synthesizes the terminal Galα1-4Gal of the P(k) (Gb3/CD77) glycosphingolipid, important in transfusion medicine, obstetrics, and pathogen susceptibility. Critical nucleotide changes in A4GALT not only abolish P(k) formation but also another Galα1-4Gal-defined antigen, P1, which belongs to the only blood group system for which the responsible locus remains undefined. Since known A4GALT polymorphisms do not explain the P1-P(k)+ phenotype, P(2), we set out to elucidate the genetic basis of P(1)/P(2). Despite marked differences (P(1) > P(2)) in A4GALT transcript levels in blood, luciferase experiments showed no difference between P(1)/P(2)-related promoter sequences. Investigation of A4GALT mRNA in cultured human bone marrow cells revealed novel transcripts containing only the noncoding exon 1 and a sequence (here termed exon 2a) from intron 1. These 5'-capped transcripts include poly-A tails and 3 polymorphic sites, one of which was P(1)/P(2)-specific among > 200 donors and opens a short reading frame in P(2) alleles. We exploited these data to devise the first genotyping assays to predict P1 status. P(1)/P(2) genotypes correlated with both transcript levels and P1/P(k) expression on red cells. Thus, P(1) zygosity partially explains the well-known interindividual variation in P1 strength. Future investigations need to focus on regulatory mechanisms underlying P1 synthesis.
Thuresson
Britt
B
Department of Clinical Immunology and Transfusion Medicine, University and Regional Laboratories, Lund, Sweden.
Westman
Julia S
JS
Olsson
Martin L
ML
D017398:Alternative Splicing; D001854:Bone Marrow Cells; D002469:Cell Separation; D005091:Exons / Q000235:genetics*; D005434:Flow Cytometry; D005838:Genotype; D005915:Globosides / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D010127:P Blood-Group System / Q000235:genetics*; D010641:Phenotype; D012150:Polymorphism, Restriction Fragment Length; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D005915:Globosides; D010127:P Blood-Group System; D020033:Protein Isoforms; D012333:RNA, Messenger; C480041:galactopyranosyl-1-4-paragloboside