Evolution of the ABO blood group gene in Japanese macaque

An integrative evolution theory of histo-blood group ABO and related genes

The ABO system is one of the most important blood group systems in transfusion/transplantation medicine. However, the evolutionary significance of the ABO gene and its polymorphism remained unknown. We took an integrative approach to gain insights into the significance of the evolutionary process of ABO genes, including those related not only phylogenetically but also functionally. We experimentally created a code table correlating amino acid sequence motifs of the ABO gene-encoded glycosyltransferases with GalNAc (A)/galactose (B) specificity, and assigned A/B specificity to individual ABO genes from various species thus going beyond the simple sequence comparison. Together with genome information and phylogenetic analyses, this assignment revealed early appearance of A and B gene sequences in evolution and potentially non-allelic presence of both gene sequences in some animal species. We argue: Evolution may have suppressed the establishment of two independent, functional A and B genes in most vertebrates and promoted A/B conversion through amino acid substitutions and/or recombination; A/B allelism should have existed in common ancestors of primates; and bacterial ABO genes evolved through horizontal and vertical gene transmission into 2 separate groups encoding glycosyltransferases with distinct sugar specificities.

The PNarec method for detection of ancient recombinations through phylogenetic network analysis

Recombinations are known to disrupt bifurcating tree structure of gene genealogies. Although recently occurred recombinations are easily detectable by using conventional methods, recombinations may have occurred at any time. We devised a new method for detecting ancient recombinations through phylogenetic network analysis, and detected five ancient recombinations in gibbon ABO blood group genes [Kitano et al., 2009. Mol. Phylogenet. Evol., 51, 465-471]. We present applications of this method, now named as "PNarec", to various virus sequences as well as HLA genes.

Relic of ancient recombinations in gibbon ABO blood group genes deciphered through phylogenetic network analysis

The primate ABO blood group gene encodes a glycosyl transferase (either A or B type), and is known to have large coalescence times among the allelic lineages in human. We determined nucleotide sequences of ca. 2.2kb of this gene for 23 individuals of three gibbon species (agile gibbon, white-handed gibbon, and siamang), and observed a total of 24 haplotypes. We found relics of five ancient intragenic recombinations, occurred during ca. 2-7 million years ago, through a phylogenetic network analysis. The coalescence time between A and B alleles estimate precede the divergence (ca. 8MYA) of siamang and common gibbon lineages. This establishes the coexistence of divergent allelic lineages of the ABO blood group gene for a long period in the ancestral gibbon species, and strengthens the non-neutral evolution for this gene.