The evolutionary origin of the HLA-DR3 haplotype

Area of Science:

• Genomics
• Evolutionary Biology
• Immunogenetics

Background:

• The human leukocyte antigen (HLA) complex plays a crucial role in immune response.
• The HLA-DR3 haplotype contains specific gene arrangements, including the HLA-DRB2 pseudogene.
• Understanding the evolutionary origins of HLA haplotypes provides insights into primate genetic diversity.

Purpose of the Study:

• To investigate the evolutionary origin of the human HLA-DR3 haplotype.
• To compare the HLA-DRB2 pseudogene with orthologous genes in gorillas and chimpanzees.

Main Methods:

• Sequencing of the human HLA-DRB2 gene and homologous genes (Gogo-DRB2, Patr-DRB2) from gorilla and chimpanzee.
• Comparative nucleotide sequence analysis of pseudogenes and other known DRB genes.
• Phylogenetic analysis to infer evolutionary relationships.

Main Results:

• The human HLA-DRB2, gorilla Gogo-DRB2, and chimpanzee Patr-DRB2 are all pseudogenes with distinct inactivating mutations.
• HLA-DRB2 and Gogo-DRB2 show a close evolutionary relationship, suggesting orthology.
• These DRB2 pseudogenes, along with other related pseudogenes, likely evolved from a common ancestor predating human-ape lineage separation.

Conclusions:

• The HLA-DRB2 pseudogene has been non-functional for at least six million years.
• The DRB2 and DRB6 pseudogenes appear to have been inactive since before the divergence of humans, gorillas, and chimpanzees.
• The human HLA-DR3 haplotype has likely maintained its current structure for over six million years.