NEW YORK (GenomeWeb) – A transcriptomic and proteomic analysis of the giant red bull ant, Myrmecia gulosa, suggested that the diverse toxins the insect produces can be traced back to a gene superfamily shared with other stinging, or aculeate, insects in a Hymenoptera order that also includes wasps and bees.
"Our results provide the first insights into the evolution of the major toxin gene superfamily of the aculeate Hymenoptera and provide a new paradigm in the functional evolution of toxins from animal venoms," corresponding author Eivind Undheim, a researcher with the University of Queensland's Centre for Advance Imaging, and his colleagues wrote.
As they reported in Science Advances this week, Undheim and his colleagues from the University of Queensland and the University of Sydney used a combination of RNA sequencing and mass spectrometry to assess venom, insect gland, venom reservoir, and/or venom duct samples from adult worker M. gulosa ants from a colony on an island off of Australia's east coast. The search uncovered peptides with glycosylation and other post-translational modifications that corresponded with an aculeatoxin gene superfamily.
"One hypothesis, based on the broad range of natural predators and prey that M. gulosa has, is that different venom peptides may have distinct tissue or cell type selectivity profiles for different membrane compositions," the authors wrote. "Under this scenario, peptides are likely to act synergistically to produce an effect, either systemically or locally on cell membranes, that is stronger than each peptide alone."
They explained that if this hypothesis is true, aculeate Hymenoptera venoms "might represent a vast library of membrane-selective peptides with potential use as research tools or even antimicrobial or anticancer drugs."
Studies going back several decades suggest that some ants, including fire ants, produce relatively simple venoms, the researchers noted. But based on a study of M. gulosa published in Science in the 1960s, along and other research results, they suspected at least some ants have the sort of polypeptide venoms described in wasps and bees.
"[T]here is accumulating evidence that … simple, largely non-peptidic ant venoms are the exception rather than the rule," the authors wrote, noting that "[f]or several species, individual venom peptides have now been isolated and characterized."
For their new analysis, the researchers used liquid chromatography-tandem mass spec to analyze giant red bull ant venom. In parallel, their RNA sequencing analysis, done using Illumina NextSeq 500 RNA instruments, revealed 14,307 gene transcripts expressed in ant venom apparatus tissues and more than 17,500 transcripts expressed in other parts of the ant body.
The RNA sequence set included some transcripts from potential toxin- or venom-associated genes not found in the proteomic analysis, the team noted. But both the transcriptomic and proteomic analyses highlighted half a dozen venom proteins and 13 peptide sequences.
The researchers subsequently looked at the functionality and mechanism of action for at least some of the venom peptides, which pointed to diverse biological activity by venom components, and the presence of multiple pain-producing peptides.
And after digging further into the peptides and their precursors, and comparing them with venom peptides from other hymenoptera insects, the authors concluded that the "venom repertoire of M. gulosa appears to be largely, although not exclusively, dominated by peptides derived from a single gene family."
"Most M. gulosa venom peptides appear to be derived from a single gene superfamily," they wrote. "This gene superfamily includes almost all peptides identified in the venoms of the aculeate Hymenoptera, and hence, we have named it the aculeatoxin superfamily."