Genome duplication and T cell immunity

Area of Science:

• Evolutionary immunology
• Comparative genomics
• Vertebrate origins of immunity

Background:

• The adaptive immune system (AIS) in jawed vertebrates, involving T cells and B cells, is ancient and highly conserved.
• Two whole-genome duplication events are hypothesized to have facilitated the evolution of the jawed vertebrate AIS.
• Jawless vertebrates possess a distinct AIS with surprising similarities to that of jawed vertebrates.

Purpose of the Study:

• To investigate the evolutionary origins of the adaptive immune system (AIS) in vertebrates.
• To explore the role of gene duplication in the emergence of T cell and B cell immunity.
• To compare the AIS of jawed and jawless vertebrates to infer ancestral immune mechanisms.

Main Methods:

• Comparative analysis of immune system components across vertebrate lineages.
• Genomic analysis to identify ohnologs (paralogous genes) involved in immune function.
• Examination of antigen receptor diversity and lymphocyte lineages in jawed and jawless vertebrates.

Main Results:

• The jawed vertebrate AIS, mediated by T cells and B cells, arose approximately 450 million years ago.
• Gene ohnologs resulting from genome duplications played crucial roles in developing key AIS components like antigen presentation and lymphocyte signaling.
• Jawless vertebrates exhibit an AIS with unique receptors but shared functional similarities, suggesting an ancestral vertebrate immune system.

Conclusions:

• The adaptive immune system (AIS) in jawed vertebrates evolved from an ancestral system present in the common ancestor of all vertebrates.
• Whole-genome duplications were pivotal in providing the genetic toolkit for the sophisticated AIS observed in jawed vertebrates.
• Evidence points towards the existence of T-lymphoid and B-lymphoid lineages in the earliest vertebrate ancestors, predating the divergence of jawed and jawless vertebrates.