Amphibian Evolution Lab, Biology Department, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Elsene, Belgium.
Wildlife Health Ghent, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
Molecules. 2020 Feb 18;25(4):912. doi: 10.3390/molecules25040912.
A wide range of frogs produce skin poisons composed of bioactive peptides for defence against pathogens, parasites and predators. While several frog families have been thoroughly screened for skin-secreted peptides, others, like the Microhylidae, have remained mostly unexplored. Previous studies of microhylids found no evidence of peptide secretion, suggesting that this defence adaptation was evolutionarily lost. We conducted transcriptome analyses of the skins of and two African microhylid species long suspected to be poisonous. Our analyses reveal 17 evolutionary related transcripts that diversified from to those of cytolytic peptides found in other frog families. The 19 peptides predicted to be processed from these transcripts, named phrynomantins, show a striking structural diversity that is distinct from any previously identified frog skin peptide. Functional analyses of five phrynomantins confirm the loss of a cytolytic function and the absence of insecticidal or proinflammatory activity, suggesting that they represent an evolutionary transition to a new, yet unknown function. Our study shows that peptides have been retained in the defence poison of at least one microhylid lineage and encourages research on similarly understudied taxa to further elucidate the diversity and evolution of skin defence molecules.
多种青蛙产生的皮肤毒物由生物活性肽组成，用于防御病原体、寄生虫和捕食者。虽然已经对几种青蛙科进行了彻底的皮肤分泌肽筛选，但其他科，如 Microhylidae，仍大多未被探索。对 Microhylidae 的先前研究没有发现肽分泌的证据，这表明这种防御适应性在进化上已经丧失。我们对两种长期被怀疑有毒的非洲 Microhylidae 物种的皮肤进行了转录组分析。我们的分析揭示了 17 个进化相关的转录本，它们从 分化而来，与其他青蛙科的细胞溶解肽多样化。从这些转录本预测的 19 个肽被命名为 Phrynomantins，表现出惊人的结构多样性，与任何以前鉴定的青蛙皮肤肽都不同。对五种 Phrynomantins 的功能分析证实了细胞溶解功能的丧失以及没有杀虫或促炎活性，这表明它们代表了向一种新的、未知的功能的进化转变。我们的研究表明，至少在 Microhylidae 的一个谱系中，肽已经被保留在防御毒液中，并鼓励对类似研究不足的分类群进行研究，以进一步阐明皮肤防御分子的多样性和进化。
