Mechanisms for evolving hypervariability: the case of conopeptides

Area of Science:

• Evolutionary Biology
• Molecular Evolution
• Genomics

Background:

• Hypervariability is common in gene families mediating organism interactions, like venom toxins.
• Marine Conus snails possess diverse venom conopeptides, making them ideal for studying hypervariability mechanisms.

Purpose of the Study:

• To investigate the evolutionary mechanisms driving hypervariability in Conus snail venom conopeptides.
• To identify specific genetic processes contributing to the rapid evolution of these sequences.

Main Methods:

• Analysis of 170 distinct conopeptide sequences from five Conus species using EST data.
• Alignment of conopeptide precursors to identify patterns in nucleotide substitution and codon usage.
• Gene tree contingency tests to assess the role of selection.

Main Results:

• Identified accelerated nucleotide substitution rates, a transversion bias, conserved cysteine codons, and a high ratio of nonsynonymous to synonymous substitutions in mature peptide domains.
• Observed significant differences in conopeptide expression levels, with a few transcripts dominating.
• Gene trees suggest recent diversifying selection, particularly on highly expressed conopeptide transcripts.

Conclusions:

• A targeted mutator mechanism, possibly involving DNA polymerase V, generates high variability in conopeptide mature domains.
• Diversifying selection acts on highly expressed variants, driving the evolution of unique sequences and explaining conopeptide hypervariability.
• This dual mechanism of mutation and selection shapes the rapid evolution of venom components in Conus snails.