Adaptive evolution at mRNA editing sites in soft-bodied cephalopods

Area of Science:

• Molecular Biology
• Evolutionary Biology
• Genomics

Background:

• Genetic variation primarily arises from DNA mutations, but post-transcriptional modifications like RNA editing also contribute to mRNA sequence diversity.
• Adenine-to-inosine (A-to-I) RNA editing is prevalent in cephalopods, frequently altering nonsynonymous sites and thus protein sequences.
• While not directly inherited, RNA editing processes are encoded in the genome, allowing them to be influenced by evolutionary selection.

Purpose of the Study:

• Investigate selection pressures on coleoid A-to-I RNA editing sites.
• Quantify the occurrence of positive selection at these editing sites.
• Analyze the relationship between RNA editing levels and the surrounding sequence context.

Main Methods:

• Studied selection regimes at coleoid A-to-I RNA editing sites.
• Estimated the prevalence of positive selection acting on these sites.
• Analyzed interdependencies between editing levels and contextual characteristics.

Main Results:

• Observed that evolutionary substitutions near edited sites mimic the effects of editing.
• Found that edited adenines are more often substituted with guanine (an inosine analog) than unedited ones.
• Demonstrated positive selection favors these guanine substitutions at heavily edited sites, indicating RNA editing promotes adaptation.

Conclusions:

• Coleoid RNA editing sites can facilitate adaptive evolution.
• RNA editing plays a general role in the molecular evolution of metazoans, as suggested by findings in cephalopods, Drosophila, and humans.