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.
Department of Clinical Immunology and Transfusion Medicine, University and Regional Laboratories, Lund, Sweden.
Britt
B
Thuresson
Julia S
JS
Westman
Martin L
ML
Olsson
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