Accurate long-read sequencing allows assembly of the duplicated RHD and RHCE genes harboring variants relevant to blood transfusion

Next-generation sequencing (NGS) technologies have transformed medical genetics. However, short-read lengths pose a limitation on identification of structural variants, sequencing repetitive regions, phasing of distant nucleotide changes, and distinguishing highly homologous genomic regions. Long-read sequencing technologies may offer improvements in the characterization of genes that are currently difficult to assess. We used a combination of targeted DNA capture, long-read sequencing, and a customized bioinformatics pipeline to fully assemble the RH region, which harbors variation relevant to red cell donor-recipient mismatch, particularly among patients with sickle cell disease. RHD and RHCE are a pair of duplicated genes located within an ∼175 kb region on human chromosome 1 that have high sequence similarity and frequent structural variations. To achieve the assembly, we utilized palindrome repeats in PacBio SMRT reads to obtain consensus sequences of 2.1 to 2.9 kb average length with over 99% accuracy. We used these long consensus sequences to identify 771 assembly markers and to phase the RHD-RHCE region with high confidence. The dataset enabled direct linkage between coding and intronic variants, phasing of distant SNPs to determine RHD-RHCE haplotypes, and identification of known and novel structural variations along with the breakpoints. A limiting factor in phasing is the frequency of heterozygous assembly markers and therefore was most successful in samples from African Black individuals with increased heterogeneity at the RH locus. Overall, this approach allows RH genotyping and de novo assembly in an unbiased and comprehensive manner that is necessary to expand application of NGS technology to high-resolution RH typing.

Preliminary study on the function of TMEM50A and its correlation with the RH genes

OBJECTIVES

The purpose of this study was to investigate the association and impact of TMEM50A on RH genes activity and function.

BACKGROUND

SMP1 is located on chromosome 1p36.11 in the RH gene locus, between the RHD and RHCE gene, where its position may be linked to RH haplotypes and contribute to selective pressures regarding certain RH haplotypes. TMEM50A is encoded by the SMP1 located in the intergenic region of RH, its influence on the function of the RH genes remains unclear.

METHODS

The expression of TMEM50A was regulated by transfection of plasmid and siRNA in K562 cell model. Western blot and real-time PCR were used to detect possible expression changes in the RH. The ammonium transport function of cells was monitored using pH-sensitive dye, while transcriptome sequencing was used to predict the potential function of TMEM50A.

RESULTS

The overexpression of TMEM50A significantly up-regulated RHCE gene activity (63.56%). The inhibition of TMEM50A resulted in significantly decreased RHCE (41.82%) and RHD expression (27.35%). Compared to control group, there was no significant change in the NH₄ ⁺ transport function of cells in the overexpressed TMEM50A group. Transcriptome analysis showed that TMEM50A not only affected the transcription of target gene through splicing activities, but also played a role in the development of embryonic nervous system.

CONCLUSIONS

TMEM50A may regulate the expression of RH gene by affecting the stability of RH mRNA through splicing function. It speculates that TMEM50A may play an important role in the development of embryonic nervous system.