The Metamorphosis of Amphibian Toxicogenomics

Abstract

Amphibians are important vertebrates in toxicology often representing both aquatic and terrestrial forms within the life history of the same species. Of the thousands of species, only two have substantial genomics resources: the recently published genome of the Pipid, Xenopus (Silurana) tropicalis, and transcript information (and ongoing genome sequencing project) of Xenopus laevis. However, many more species representative of regional ecological niches and life strategies are used in toxicology worldwide. Since Xenopus species diverged from the most populous frog family, the Ranidae, ~200 million years ago, there are notable differences between them and the even more distant Caudates (salamanders) and Caecilians. These differences include genome size, gene composition, and extent of polyploidization. Application of toxicogenomics to amphibians requires the mobilization of resources and expertise to develop de novo sequence assemblies and analysis strategies for a broader range of amphibian species. The present mini-review will present the advances in toxicogenomics as pertains to amphibians with particular emphasis upon the development and use of genomic techniques (inclusive of transcriptomics, proteomics, and metabolomics) and the challenges inherent therein.

The plasticizer bisphenol A affects somatic and sexual development, but differently in pipid, hylid and bufonid anurans

“…Not surprisingly, these complex differences appear to cause susceptibility differences to endocrine disruption (cf. Helbing, 2012). From our results, it seems obvious that these toxicological differences will translate into species differences of adverse effects.…”

“…No species can be easily called more or less vulnerable, as responses to BPA differ strikingly. More than 200 Million years of divergence between Pipidae, Bufonidae and Hylidae, and about 100 My between the latter two anuran families (www.timetree.org), have led to the evolution of profound differences in genome size and composition with ecotoxicological relevance (Helbing, 2012), various life history and ecologies including larval feeding (Avila and Frye, 1978;Degani, 1986;Schneider and Grosse, 2009;St€ ock et al, 2009), as well as physiology (Wilbur, 1980) and sex determination pathways (e.g. Berset-Br€ andli et al, 2006;St€ ock et al, 2011aSt€ ock et al, , 2011bTamschick et al, 2015;Yoshimoto et al, 2008).…”

“…The Pipidae diverged from the Neobatrachia, including Bufonidae and Hylidae, more than 206 million years ago (www.timetree.org), and there are notable differences in their ecotoxicologically relevant genome composition (e.g. Helbing, 2012), feeding behavior and ecology (Avila and Frye, 1978;Degani, 1986;Wilbur, 1980;Schneider and Grosse, 2009;St€ ock et al, 2009;www.amphibiaweb. org).…”

Phenotypic plasticity in the hepatic transcriptome of the European common frog (Rana temporaria): the interplay between environmental induction and geographical lineage on developmental response

“…As expected (Helbing et al . ; Helbing ), transcript levels for thrb and cps1 were significantly higher in the Gosner stage 37 tadpoles compared with those in day 14 (Gosner stage 31–35) (Fig. ).…”

“…This includes changes in the expression status of genes important in induction of the metamorphic programme such as the thyroid hormone receptors, thra and thrb , and the activation of urea cycle genes in preparation for the animal's transition from life in water to land (Helbing et al . , ; Helbing ; Searcy et al . ).…”