Metabolomic insights into system-wide coordination of vertebrate metamorphosis

Abstract

BackgroundAfter completion of embryogenesis, many organisms experience an additional obligatory developmental transition to attain a substantially different juvenile or adult form. During anuran metamorphosis, the aquatic tadpole undergoes drastic morphological changes and remodelling of tissues and organs to become a froglet. Thyroid hormones are required to initiate the process, but the mechanism whereby the many requisite changes are coordinated between organs and tissues is poorly understood. Metabolites are often highly conserved biomolecules between species and are the closest reflection of phenotype. Due to the extensive distribution of blood throughout the organism, examination of the metabolites contained therein provides a system-wide overview of the coordinated changes experienced during metamorphosis. We performed an untargeted metabolomic analysis on serum samples from naturally-metamorphosing Rana catesbeiana from tadpoles to froglets using ultraperformance liquid chromatography coupled to a mass spectrometer. Total and aqueous metabolite extracts were obtained from each serum sample to select for nonpolar and polar metabolites, respectively, and selected metabolites were validated by running authentic compounds.ResultsThe majority of the detected metabolites (74%) showed statistically significant abundance changes (padj < 0.001) between metamorphic stages. We observed extensive remodelling of five core metabolic pathways: arginine and purine/pyrimidine, cysteine/methionine, sphingolipid, and eicosanoid metabolism and the urea cycle, and found evidence for a major role for lipids during this postembryonic process. Metabolites traditionally linked to human disease states were found to have biological linkages to the system-wide changes occuring during the events leading up to overt morphological change.ConclusionsTo our knowledge, this is the first wide-scale metabolomic study of vertebrate metamorphosis identifying fundamental pathways involved in the coordination of this important developmental process and paves the way for metabolomic studies on other metamorphic systems including fish and insects.

Chytridiomycosis causes catastrophic organism-wide metabolic dysregulation including profound failure of cellular energy pathways

“…Pantothenate (otherwise known as vitamin B 5 ) is an essential water-soluble vitamin for the synthesis of coenzyme-A (CoA) which is principally involved in energy (tricarboxylic acid cycle) and fatty acid metabolism. This metabolite is also essential for the growth of pathogenic organisms, including fungi 83 , and has been previously measured in developing frogs 84 . Analogues of pantothenate have even shown antimicrobial capabilities, as they prevent the uptake of the naturally occurring endogenous and essential metabolites 85 , 86 .…”

Cross‐Taxa Distinctions in Mechanisms of Developmental Effects for Aquatic Species Exposed to Trifluralin

“…Accelerated metamorphosis in response to the environmental stressor of pond drying is associated with oxidative stress and increased antioxidant enzymes (Gomez Mestre et al 2013). Significant changes in metabolite abundance during metamorphosis in Rana catesbeiana identified the importance of lipids during this process (Ichu et al 2014). The stage during which tadpoles were sampled in that study is typically associated with decreased glutathione, increasing lipid peroxide, and increased ascorbic acid in X. laevis as remodeling of organs is nearing completion and tail resorption is imminent (Menon and Rozman 2007).…”

Biomarker analysis of American toad (Anaxyrus americanus) and grey tree frog (Hyla versicolor) tadpoles following exposure to atrazine

“… Ichu et al (2014) described how metabolic profiles changed during amphibian larval development. Many of the altered metabolites that changed in tadpoles exposed to high levels of atrazine were also identified as dynamic based on larval stage.…”

“…The highest overlap was in the urea cycle, arginine, and purine/pyrimidine metabolism pathway. Metabolites involved in purine metabolism, urea cycle, and arginine and pyrimidine metabolism have demonstrated significant abundance fluxes as frogs undergo metamorphosis ( Ichu et al, 2014 ); the aforementioned pathways have many metabolites in common (Fig. 7).…”

“… Zaya et al (2011a , b) examined changes in gene expression to link atrazine exposure to changes in pathways converting lipids and proteins into energy and carbohydrate metabolism, fat storage, and protein synthesis in Xenopus laevis . Metabolomics was used to explore how the metabolome changes in early larval amphibian development and across all stages of frog development ( Vastag et al, 2011 ; Ichu et al, 2014 ). Both studies found statistically significant changes in metabolite abundance corresponding to developmental stage.…”