Characterization of Lamprey BAFF-like Gene: Evolutionary Implications

Area of Science:

• Evolutionary immunology
• Comparative genomics
• Vertebrate immune systems

Background:

• B-cell activating factor (BAFF) and A Proliferation-Inducing Ligand (APRIL) regulate lymphocyte survival in mammals.
• BAFF/APRIL-like molecule (BALM) exists in fish, and a BAFF-like gene is identified in lampreys.

Purpose of the Study:

• To investigate the evolutionary history of BAFF, APRIL, and related immune genes in vertebrates.
• To characterize the lamprey BAFF-like gene and its evolutionary relationship to mammalian BAFF and APRIL.

Main Methods:

• Phylogenetic analysis of BAFF, APRIL, BALM, and TWEAK genes across vertebrate lineages.
• Gene expression analysis of the lamprey BAFF-like gene in immune cells.
• Sequence similarity analysis of the lamprey BAFF-like protein with mammalian BAFF and APRIL.

Main Results:

• An ancestral BAFF and APRIL homolog was present before jawed and jawless vertebrates diverged; TWEAK evolved later in jawed vertebrates.
• The lamprey BAFF-like gene is expressed in T-like, B-like, and innate immune cells, showing higher similarity to mammalian BAFF.
• BAFF orthologs are widespread in jawed vertebrates, but APRIL and BALM are absent in some species (e.g., tetrapods lack BALM, birds lack APRIL and TWEAK).

Conclusions:

• The study elucidates the evolutionary trajectory of key immune regulators, BAFF and APRIL, from early vertebrates to mammals.
• The findings highlight gene loss and fusion events, such as the evolution of TWE-PRIL in mammals, shaping immune system diversity.
• The lamprey BAFF-like gene represents an ancient form, contributing to our understanding of immune system evolution in jawless fish.