Low structural variation in the host-defense peptide repertoire of the dwarf clawed frog Hymenochirus boettgeri (Pipidae).
THE skin secretion of many amphibians contains peptides that are able to kill a broad range of microorganisms (antimicrobial peptides: AMPs) and potentially play a role in innate immune defense. Similar to the toxin arsenals of various animals, amphibian AMP repertoires typically show major structural variation, and previous studies have suggested that this may be the result of diversifying selection in adaptation to a diverse spectrum of pathogens. Here we report on transcriptome analyses that indicate a very different pattern in the dwarf clawed frog H. boettgeri. Our analyses reveal a diverse set of transcripts containing two to six tandem repeats, together encoding 14 distinct peptides. Five of these have recently been identified as AMPs, while three more are shown here to potently inhibit the growth of gram-negative bacteria, including multi-drug resistant strains of the medically important Pseudomonas aeruginosa. Although the number of predicted peptides is similar to the numbers of related AMPs in Xenopus and Silurana frog species, they show significantly lower structural variation. Selection analyses confirm that, in contrast to the AMPs of other amphibians, the H. boettgeri peptides did not evolve under diversifying selection. Instead, the low sequence variation among tandem repeats resulted from purifying selection, recent duplication and/or concerted gene evolution. Our study demonstrates that defense peptide repertoires of closely related taxa, after diverging from each other, may evolve under differential selective regimes, leading to contrasting patterns of structural diversity.
Amphibian Evolution Lab, Biology Department, Vrije Universiteit Brussel, Brussels, Belgium.
Severine
S
Matthijs
Department of Bioengineering Sciences, Research Group of Microbiology and Vlaams Instituut voor Biotechnologie, Vrije Universiteit Brussel, Brussels, Belgium.
Lumeng
L
Ye
Unit of Cellular and Molecular Immunology, Vrije Universiteit Brussel, Brussels, Belgium ; Laboratory of Myeloid Cell Immunology, Vlaams Instituut voor Biotechnologie, Brussels, Belgium.
Benoit
B
Stijlemans
Department of Bioengineering Sciences, Research Group of Microbiology and Vlaams Instituut voor Biotechnologie, Vrije Universiteit Brussel, Brussels, Belgium.
Pierre
P
Cornelis
Amphibian Evolution Lab, Biology Department, Vrije Universiteit Brussel, Brussels, Belgium.
Franky
F
Bossuyt
Amphibian Evolution Lab, Biology Department, Vrije Universiteit Brussel, Brussels, Belgium.
Kim
K
Roelants
D000595:Amino Acid Sequence; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D001419:Bacteria / Q000187:drug effects; D016000:Cluster Analysis; D019143:Evolution, Molecular; D014644:Genetic Variation; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010802:Phylogeny; D010884:Pipidae / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D012867:Skin / Q000378:metabolism; D014158:Transcription, Genetic
D023181:Antimicrobial Cationic Peptides