A singular shark bitter taste receptor provides insights into the evolution of bitter taste perception

Area of Science:

• Evolutionary biology
• Sensory systems
• Molecular biology

Background:

• Toxic compounds are detected by taste 2 receptors (T2Rs), which mediate bitter taste.
• T2Rs have been identified in bony vertebrates, but their evolutionary history in other groups remained unclear.
• Cartilaginous fish, like sharks, represent an important lineage for understanding vertebrate evolution.

Purpose of the Study:

• To investigate the evolutionary origin and function of bitter taste receptors (T2Rs) in cartilaginous fish.
• To identify T2Rs in various shark, sawfish, and skate species.
• To compare the ligand repertoire and functional conservation of cartilaginous fish T2Rs with those of bony vertebrates.

Main Methods:

• Genomic analysis of cartilaginous fish to identify T2R genes.
• Ligand screening using two shark species (catshark and bamboo shark).
• Comparative analysis of T2R sequences and ligand responses across different vertebrate groups.

Main Results:

• A single T2R gene was identified in 12 cartilaginous fish species, forming a sister clade to bony fish T2Rs.
• Shark T2Rs responded to bitter compounds like amarogentin and endogenous steroids.
• Functional conservation of ligand recognition was observed between shark and basal bony fish T2Rs over ~500 million years.
• Shark T2Rs exhibit a broader ligand repertoire, including xenobiotics, similar to ancestral receptors.

Conclusions:

• The cartilaginous fish T2R represents an ancestral form, providing insights into the early evolution of bitter taste perception.
• Functional conservation of T2Rs highlights their crucial role in detecting potentially harmful substances throughout vertebrate evolution.
• The findings suggest that the ancestral T2R recognized a wider range of compounds, with subsequent specialization in bony vertebrates.