An Ancient Adenosine Receptor Gains Olfactory Function in Bony Vertebrates

Area of Science:

• Evolutionary biology
• Neuroscience
• Genetics

Background:

• Nucleotides are crucial odorants for aquatic vertebrates and have signaling roles in cellular processes.
• An adenosine receptor (adora2 clade) was recently identified as a zebrafish olfactory receptor.

Purpose of the Study:

• To investigate the evolutionary history of the adorb gene and its olfactory function.
• To understand the functional divergence of adorb across vertebrate lineages.

Main Methods:

• Phylogenetic analysis across vertebrates, chordates, and ambulacraria.
• Gene expression pattern analysis in olfactory epithelia of various species (zebrafish, eel, carp, clawed frog, lamprey).
• Double-labeling experiments in lamprey to identify cell types expressing adorb.

Main Results:

• The adorb gene originated as a sister clade to the adora family in the common ancestor of vertebrates, chordates, and ambulacraria.
• adorb is expressed in olfactory epithelia of zebrafish, eel, carp, and clawed frog, suggesting an olfactory receptor function.
• Lamprey adorb expression is in nonneuronal progenitor cells, not the sensory olfactory region, indicating a different role.

Conclusions:

• The adorb gene likely evolved olfactory receptor function in jawed vertebrates.
• A functional switch of adorb from a nonneuronal role to an olfactory receptor role may have occurred during vertebrate evolution.