Characterization of the mouse Rh blood group gene

Generation of mice with inactivated Rh or Rhag genes

Mice carrying inactivated Rh and Rhag genes were generated by insertional targeting. KO animals exhibited normal growth, development and fertility and both types were indistinguishable at a gross phenotypic level from their wild type littermates. Preliminary analysis revealed that red cells from Rh-/- mice lack Rh protein and have a moderate decrease of Rhag protein, whereas those from Rhag-/- mice have a total absence of Rhag and Rh proteins. Studies are in progress to delineate the antigenic, biochemical and functional abnormalities of red cells from these animals as well as the impact on hematological parameters and erythropoiesis.

Entire sequence of a mouse chromosomal segment containing the gene Rhced and a comparative analysis of the homologous human sequence

The mouse genomic sequence of the region containing the gene Rhced, the orthologue to the human gene RH30, was determined to elucidate the structure of Rhced and its flanking regions and to compare these with the corresponding human genomic region. Two genes, Smp1 and AK003528 (an orthologue of FLJ10747), flank Rhced. Neither sequences homologous to the characteristic nucleotide elements flanking the RHD gene in humans (rhesus boxes) nor an additional Rh gene were found within the mouse region sequenced. This result and that of a previous report demonstrate that this chromosomal region of the mouse comprises five genes (FLJ10747-RHCE-SMP1-NPD014-P29) that exhibit syntenic homology with the corresponding human region, which suggests that the RHD gene and rhesus boxes were inserted later. Evaluations of tissue distribution and subcellular localization of these genes indicate that the SMP1 orthologue has a ubiquitous tissue distribution and cytoplasmic localization, whereas AK003528 is expressed slightly higher in testis with a strong subcellular localization in the nucleus. Despite the steady improvements in the draft sequence of the human genome, this study demonstrates the continuing benefits of comparative genetic analyses in increasing our understanding of human genomic structure.

The evolution and formation of RH genes

The Rh system clinically is one of the important blood groups. The major Rh antigens, which are constituted by over 40 types, are RhD, RhC/c, and RhE/e. Furthermore, Rh blood group system is characterized by the existence of many variants. It was considered that Rh blood group system was encoded on two genes termed the RHCE and RHD, which are composed of ten exons, respectively. It is inferred that the RHD gene encodes the RhD antigen and that the RHCE gene encodes the Rh C/c and RhE/e antigens. There are RHce, RHCe, RHcE and RHCE alleles as polymorphisms of RHCE gene. In 2000, the entire nucleotide sequences in all introns of both the RHD and RHCE genes were determined. Due to the new findings on RH genes, it is thought that multiple recombination (and/or gene conversion), nucleotide substitutions, small nucleotide gaps, replication slippage of microsatellite, large nucleotide gaps (due to Alu sequence) and the high level of the homology (%) between both RH genes are the important factors in the formation and evolution of both RH genes and Rh variants. Based on the advance of human genome project, the new interpretations on the evolution and formation of RH genes and Rh variants will be performed. Human Rh family (superfamily) and its counterparts in primates, mammals, fish, amphibians, bacteria, lower eukaryotes, archaea and plants have been identified. A lot of findings have been accumulated in their evolution and function. As gene conversions or recombination events confuse the phylogenetic tree of human RH genes and their counterparts, careful attention is necessary for researchers to calculate the time of gene duplication and to discuss the evolution of Rh family and its counterparts.Rh genotyping methods will never be perfect and both the clinicians and researchers have to recognize the limitation of Rh genotyping, especially RhD genotyping, because new Rh variants must have formed continually. In applying the Rh genotyping to clinical medicine, especially transfusion medicine, it is necessary to compare and examine the serological (phenotypic) data in Rh blood group system with caution.

The analysis of nucleotide substitutions, gaps, and recombination events between RHD and RHCE genes through complete sequencing

We determined the entire nucleotide sequences of all introns within the RHD and RHCE genes by amplifying genomic DNA using long PCR methods. The RHD and RHCE genes were 57,295 and 57,831 bp in length, respectively. Aligning both genes revealed 138 gaps (insertions and deletions) below 100 bp, 1116 substitutions in all introns and all exons (coding region), and 5 gaps of over 100 bp. Homologies (%) between the RH genes were 93.8% over all introns and coding exons and 91.7% over all exons and introns. Various short tandem repeats (STRs) and many interspersed nuclear elements were identified in both genes. The proportions of Alu sequences in the RHD and RHCE genes were 25.9 and 25.7%, respectively and these Alu sequences were concentrated in several regions. We confirmed multiple recombinations in introns 1 and 2. Such multiple recombination, which probably arose due to the concentrations of Alu sequences and the high level of the homology (%), is one of most important factors in the formation and evolution of RH gene. The variability of the Rh system may be generated because of these features of RH genes. Apparent mutational hotspots and regions with low of K values (the numbers of substitutions per nucleotide site) caused by recombinations as well as true mutational hotspots may be found in human genome. Accordingly, in searching for and identifying single nucleotide polymorphisms (SNPs) especially in noncoding regions, apparent mutational hotspots and areas of low K values by recombination should be noted since the unequal distribution of SNPs will reduce the power of SNPs as genetic maker. Combining the complete sequences' data of both RH genes with serological findings will provide beneficial information with which to elucidate the mechanism of recombination, mutation, polymorphism, and evolution of other genes containing the RH gene as well as to analyze Rh variants and develop new methods of Rh genotyping.

Evidence supporting the requirement for two proline residues for expression of c

BACKGROUND

In humans, c antigen expression is associated with a proline residue at amino acid position 103 in the second extracellular loop of the CE protein. Comparison of nonhuman primate Rh proteins suggested that c reactivity might actually involve two proline residues. It has been shown that the RBCs of New World capuchin monkeys (Cebus apella) react with anti-c. To further define the amino acid residues involved in c expression, Rh cDNA from the capuchin was analyzed.

STUDY DESIGN AND METHODS

Rh transcripts were amplified by reverse transcription PCR from RNA isolated from the reticulocytes of a capuchin monkey and were cloned and sequenced.

RESULTS

Rh transcripts from the capuchin monkey, whose RBCs react with anti-c, were found to encode adjacent proline residues at 102 and 103.

CONCLUSION

Sequencing of Rh transcripts from the capuchin monkey supports the hypothesis that the expression of c requires two adjacent proline residues. Proline causes bends or loops in proteins, which, in this case, might form a unique, stable structure resistant to perturbations induced by changes in upstream or downstream residues. This would explain the scarcity in humans of c variants as compared to the other major Rh antigen variants, and the preservation of c reactivity despite 24-percent divergence between the human and capuchin Rh proteins.