Mechanisms of antigen receptor evolution

Area of Science:

• Evolutionary immunology
• Molecular biology
• Genetics

Background:

• The adaptive immune system, crucial for recognizing pathogens, emerged in jawed vertebrate ancestors ~500 million years ago.
• Key components like immunoglobulins (Igs), T cell receptors (TCRs), and recombination-activating genes (RAGs) are found in jawed vertebrates but not in jawless or invertebrate species.
• The exact nature of the primordial antigen receptor that preceded RAG-mediated recombination remains unknown.

Purpose of the Study:

• To investigate the evolutionary origins and diversification mechanisms of immune receptors.
• To explore RAG-mediated and alternative pathways for generating immune receptor diversity in various species.
• To understand the transition from primordial receptors to the Ig/TCR-like domains found in jawed vertebrates.

Main Methods:

• Genomic analyses of jawless vertebrates, protochordates, and other invertebrate deuterostomes.
• Protein functional analyses in model systems.
• Comparative studies of gene homologs and their distribution across taxa.

Main Results:

• Homologs of key adaptive immune genes (Igs, TCRs, MHC, RAGs) are specific to jawed vertebrates.
• Diverse immune receptor families, including non-diversified and diversified Ig-type variable regions, exist.
• Studies in invertebrates reveal novel mechanisms for generating receptor diversity beyond RAG-mediated recombination.

Conclusions:

• The adaptive immune system's core components evolved in jawed vertebrates.
• Immune receptor diversity is generated through various mechanisms, including RAG-dependent and independent pathways.
• Ongoing research in invertebrate models continues to uncover new insights into immune receptor evolution and function.