Michael J. Tyler

Host-defence peptides of Australian anurans: structure, mechanism of action and evolutionary significance.

Host-defence peptides secreted from the skin glands of Australian frogs and toads, are, with a few notable exceptions, different from those produced by anurans elsewhere. This review summarizes the current knowledge of the following classes of peptide isolated and characterized from Australian anurans: neuropeptides (including smooth muscle active peptides, and peptides that inhibit the production of nitric oxide from neuronal nitric oxide synthase), antimicrobial and anticancer active peptides, antifungal peptides and antimalarial peptides. Other topics covered include sex pheromones of anurans, and the application of peptide profiling to (i). recognize particular populations of anurans of the same species and to differentiate between species, and (ii). investigate evolutionary aspects of peptide formation.

Population trends associated with skin peptide defenses against chytridiomycosis in Australian frogs

Many species of amphibians in the wet tropics of Australia have experienced population declines linked with the emergence of a skin-invasive chytrid fungus, Batrachochytrium dendrobatidis. An innate defense, antimicrobial peptides produced by granular glands in the skin, may protect some species from disease. Here we present evidence that supports this hypothesis. We tested ten synthesized peptides produced by Australian species, and natural peptide mixtures from five Queensland rainforest species. Natural mixtures and most peptides tested in isolation inhibited growth of B. dendrobatidis in vitro. The three most active peptides (caerin 1.9, maculatin 1.1, and caerin 1.1) were found in the secretions of non-declining species (Litoria chloris, L. caerulea, and L. genimaculata). Although the possession of a potent isolated antimicrobial peptide does not guarantee protection from infection, non-declining species (L. lesueuri and L. genimaculata) inhabiting the rainforest of Queensland possess mixtures of peptides that may be more protective than those of the species occurring in the same habitat that have recently experienced population declines associated with chytridiomycosis (L. nannotis, L. rheocola, and Nyctimystes dayi). This study demonstrates that in vitro effectiveness of skin peptides correlates with the degree of decline in the face of an emerging pathogen. Further research is needed to assess whether this non-specific immune defense may be useful in predicting disease susceptibility in other species.

Aquatic sex pheromone from a male tree frog.

Many creatures use chemical signals (pheromones) as sources of information about the world around them. For example, a sex pheromone produced by one sex (usually the female) of a particular species induces an immediate behavioural response in the opposite sex of the same species. However, very little is known about amphibian pheromones. We have now discovered and characterized an aquatic, female-attracting pheromone from the parotoid and rostral glands of a male frog, the magnificent tree frog, Litoria splendida. To our knowledge, this pheromone, which we have named splendipherin, is the first pheromone from an anuran (frog or toad) to be identified.

Antimicrobial Peptides from Amphibian Skin Potently Inhibit Human Immunodeficiency Virus Infection and Transfer of Virus from Dendritic Cells to T Cells

ABSTRACT Topical antimicrobicides hold great promise in reducing human immunodeficiency virus (HIV) transmission. Amphibian skin provides a rich source of broad-spectrum antimicrobial peptides including some that have antiviral activity. We tested 14 peptides derived from diverse amphibian species for the capacity to inhibit HIV infection. Three peptides (caerin 1.1, caerin 1.9, and maculatin 1.1) completely inhibited HIV infection of T cells within minutes of exposure to virus at concentrations that were not toxic to target cells. These peptides also suppressed infection by murine leukemia virus but not by reovirus, a structurally unrelated nonenveloped virus. Preincubation with peptides prevented viral fusion to target cells and disrupted the HIV envelope. Remarkably, these amphibian peptides also were highly effective in inhibiting the transfer of HIV by dendritic cells (DCs) to T cells, even when DCs were transiently exposed to peptides 8 h after virus capture. These data suggest that amphibian-derived peptides can access DC-sequestered HIV and destroy the virus before it can be transferred to T cells. Thus, amphibian-derived antimicrobial peptides show promise as topical inhibitors of mucosal HIV transmission and provide novel tools to understand the complex biology of HIV capture by DCs.

The Maculatin peptides from the skin glands of the tree frog Litoria genimaculata: a comparison of the structures and antibacterial activities of Maculatin 1.1 and Caerin 1.1

Six peptides have been isolated and characterized from the dorsal glands of the tree frog Litoria genimaculata. One of these is the known hypotensive peptide caerulein; the others have been named maculatins. The amino acid sequences of the maculatin peptides have been determined using a combination of fast atom bombardment mass spectrometry and automated Edman sequencing. Four of the maculatin peptides show antibiotic activity, with maculatin 1.1 [GLFGVLAKVAAHVVPAIAEHF(NH2;)] showing the most pronounced activity, particularly against Gram‐positive organisms. Maculatin 1.1 resembles the known caerin 1 antibiotic peptides, except that four of the central amino acid residues (of the caerin 1 system) are missing in maculatin 1.1. A comparison of the antibiotic activity of maculatin 1.1 with those of caerin 1.1 is reported. ©1998 European Peptide Society and John Wiley & Sons, Ltd.

Antipredator Mechanisms of Australian Frogs

We examined the antipredator mechanisms of 19 Australian hylid species (two genera) and 23 myobatrachid species (nine genera). Frogs of 39 of the 42 species exhibited one or more defensive mech- anisms (other than escape), including postures, bright coloration, adhesive skin secretions, and/or calls. De- fensive posturing occurred in individuals of 38 species, and varied in relationship to morphology and lo- calization of skin glands. Bright colors, when present, typically were displayed during defensive postures. We documented dramatic geographic variation in the antipredator display of one species, Limnodynastes tasmaniensis. Defensive postures were accompanied by secretions from dorsal skin glands. These secretions were sometimes associated with a distinctive odor. Adhesive skin secretions were present in burrowing frogs of three genera. Defensive calls were emitted by most hylids but none of the myobatrachids. We offer a hypothesis of mimicry to explain the behavior pattern of exposing the bold black and white ventral surface in Pseudophryne and Crinia species.

New caerin antibacterial peptides from the skin glands of the Australian tree frog Litoria xanthomera

The secretion of the skin glands of the ‘orange‐thighed frog’ Litoria xanthomera contains seven peptides. One of these is the known hypotensive peptide caerulein. Two new peptides, caerin 1.6 [GLFSVLGAVAKHVLPHVVPVIAEKL(NH2)], and caerin 1.7 [GLFKVLGSVAKHLLPHVAPVIAEKL(NH2)] show antibacterial properties. Two other peptides lack the first two amino acid residues of caerins 1.6 and 1.7 and show no antibacterial activity. The identification of the peptides in Litoria xanthomera confirms that this species is related to Litoria caerula, Litoria gilleni and Litoria splendida but not as closely as those three species are related to each other.

The antibiotic and anticancer active aurein peptides from the Australian Bell Frogs Litoria aurea and Litoria raniformis. Part 2. Sequence determination using electrospray mass spectrometry.

Sixteen aurein peptides are present in the host defence secretion from the granular dorsal glands of the Green and Golden Bell Frog Litoria aureus and seventeen from those of the related Southern Bell Frog Litoria raniformis. All peptides have been sequenced using a combination of electrospray mass spectrometry and Lys-C digestion, with each sequence confirmed by automated Edman sequencing. The peptides are named in five groups, viz. aureins 1-5. Ten of these peptides are common to both species of frog. Thirteen of the aurein peptides show wide-spectrum antibiotic and anticancer activity. Amongst the more active peptides are aurein 1.2 (GLFDIIKKIAESF-NH2), the smallest peptide from an anuran reported to have both antibiotic and anticancer activity; aurein 2.2 (GLLDIVKKVIGAFGSL-NH2) and aurein 3.1 (GLFDIVKKIAGHIAGSI-NH2). The aurein 4 and 5 peptides, e.g. aurein 4.1 (GLIQTIKEKLKELAGGLVTGIQS-OH) and aurein 5.1 (GLLDIVTGLLGNLIVDVLKPKTPAS-OH), show neither antibacterial nor anticancer activity.

Gastric Brooding: Unique Form of Parental Care in an Australian Frog

The recently described leptodactylid frog Rheobatrachus silus of Queensland, Australia, exhibits a unique form of parental care. The female carries embryos and young in the stomach, propulsively ejecting the juveniles.

Toxicity of herbicide formulations to frogs and the implications for product registration: A case study from Western Australia

Growing concern about the decline of amphibian populations has highlighted the need to assess the potential impact of agricultural chemicals on these animals. Although the relative sensitivity of amphibians to the toxic effects of pesticides and other environmental contaminants has yet to be established, the perceived vulnerability of amphibians to pesticide effects may actually be attributable to their specific habitat requirements. Shallow temporary ponds, essential to the life cycles of many amphibians, are also areas where pollutants may accumulate without substantial dilution. Research in Western Australia has highlighted the potential risk that agricultural chemicals may pose to fauna that inhabit low dilution environments, and indicates that the data currently required for pre-registration assessment of pesticides may be inadequate to effectively protect these environments.