The molecular genetic background leading to the formation of the human erythroid-specific Xga/CD99 blood groups

Abstract

The Xg and CD99 antigens of the human Xg blood group system show a unique and sex-specific phenotypic relationship. The phenotypic relationship is believed to result from transcriptional coregulation of the and genes, which span the pseudoautosomal boundary of the X and Y chromosomes. However, the molecular genetic background responsible for these blood groups has remained undetermined. During the present investigation, we initially conducted a pilot study aimed at individuals with different Xg/CD99 phenotypes; this used targeted next-generation sequencing of the genomic areas relevant to and This was followed by a large-scale association study that demonstrated a definite association between a single nucleotide polymorphism (SNP) rs311103 and the Xg/CD99 blood groups. The G and C genotypes of SNP rs311103 were associated with the Xg(a+)/CD99H and Xg(a-)/CD99L phenotypes, respectively. The rs311103 genomic region with the G genotype was found to have stronger transcription-enhancing activity by reporter assay, and this occurred specifically with erythroid-lineage cells. Such activity was absent when the same region with the C genotype was investigated. In silico analysis of the polymorphic rs311103 genomic regions revealed that a binding motif for members of the GATA transcription factor family was present in the rs311103[G] region. Follow-up investigations showed that the erythroid GATA1 factor is able to bind specifically to the rs311103[G] region and markedly stimulates the transcriptional activity of the rs311103[G] segment. The present findings identify the genetic basis of the erythroid-specific Xg/CD99 blood group phenotypes and reveal the molecular background of their formation.

A whole genome approach for discovering the genetic basis of blood group antigens: independent confirmation for P1 and Xga

“…As a proof of principle, we used WGS data and limited paired serologic typing to identify NT changes correlated with P1 and Xg a expression. This analysis was done prior to the recent publications detailing the role of RUNX1 GATA‐1 and transcription factor binding in expression of these antigens, and is independent confirmation of those reports. Importantly, since the entire genomic sequence was available for analysis, we could rule out the possibility of other common NT changes controlling P1 and Xg a expression in the A4GALT and XG genes and upstream promoter regions.…”

“…The combined frequency and serologic approach was successful in determining the molecular basis of Xg a expression as it identified just one potential NT change, rs311103. This is the same change recently reported to contain a GATA‐1 transcription factor–binding region controlling Xg a expression . We determined that genotyping of Xg a from males will prove difficult due to the homologous PAR1 region shared by chromosomes X and Y.…”

“…However, this gap is quickly closing as bioinformatics technologies are applied. For example, recent work has provided evidence for the role of the transcription factors RUNX1 in the expression of P1 antigen and of GATA‐1 in the expression of Xg a …”

“…In 1994, it was shown that Xg a was expressed on the protein product of PBDX (renamed XG ) in a manner that suggested that antigen expression was controlled by the presence or absence of Xg protein, but the mechanism remained unknown. Recently, Moller et al and Yeh et al showed that the SNP rs311103 (NT G > C) is located in a GATA‐1 transcription factor binding region in intron 1 of XG , and controls the expression of the protein and the Xg a antigen with genomic coordinate chrX:26,66,384G associated with Xg(a+) and chrX:26,66,384C associated with a Xg(a–) phenotype.…”

A large deletion spanning XG and GYG2 constitutes a genetic basis of the Xgnull phenotype, underlying anti‐Xga production

“…Furthermore, no antithetical antigen has been reported. Recently, Xg glycoprotein expression on RBCs was demonstrated to be regulated by GATA1 binding to a control element 3.7 kb upstream of XG and the rs311103C single nucleotide polymorphism abolishes expression, resolving this fundamental question more than 5 decades after the antigen was discovered. However, despite the relatively high frequencies of Xg(a−) individuals, producers of anti‐Xg a are rare, and more than 85% of those reported have been men .…”