Quantity - but not diversity - of secreted peptides and proteins increases with age in the tree frog Pithecopus nordestinus.

Douglas O Mariano,Juliana M Sciani,Katia Conceição,Carlos Jared,Daniel C Pimenta,Marta M Antoniazzi

doi:10.1590/1678-9199-jvatitd-2020-0105

Abstract

Background:Amphibians inhabit the terrestrial environment, a conquest achieved after several evolutionary steps, which were still insufficient to make them completely independent of the aquatic environment. These processes gave rise to many morphological and physiological changes, making their skin (and cutaneous secretion) rich in bioactive molecules. Among the tree frogs, the secretion is composed mainly of peptides; but alkaloids, proteins and steroids can also be found depending on the species. The most known class of biologically active molecules is the antimicrobial peptides (AMPs) that act against bacteria, fungi and protozoans. Although these molecules are well-studied among the hylids, AMPs ontogeny remains unknown. Therefore, we performed peptidomic and proteomic analyses of Pithecopus nordestinus (formerly Phyllomedusa nordestina) in order to evaluate the peptide content in post-metamorphosed juveniles and adult individuals.Methods: Cutaneous secretion of both life stages of individuals was obtained and analyzed by LC-MS/MS after reduction and alkylation of disulfide bonds or reduction, alkylation and hydrolysis by trypsin.Results: Differences in the TIC profile of juveniles and adults in both treatments were observed. Moreover, the proteomic data revealed known proteins and peptides, with slight differences in the composition, according to the life stage and the treatment. AMPs were identified, and bradykinin-potentiating peptides were observed in trypsin-treated samples, which suggests a protein source of such peptide (cryptide).Conclusion: In general, skin secretion contents were similar between juveniles and adults, varying in quantity, indicating that the different stages of life are reflected in the number of molecules and not on their diversity.

Highlights

Amphibians inhabit the terrestrial environment, a conquest achieved after several evolutionary steps, which were still insufficient to make them completely independent of the aquatic environment
The results revealed a higher diversity and quantity of bufadienolides in the eggs, which decreased during the tadpole phase and returned to rise after metamorphosis
The proteomic data for each experimental condition were processed by Peaks Studio V 7.0, using the default parameters

Summary

Introduction

Amphibians inhabit the terrestrial environment, a conquest achieved after several evolutionary steps, which were still insufficient to make them completely independent of the aquatic environment These processes gave rise to many morphological and physiological changes, making their skin (and cutaneous secretion) rich in bioactive molecules. The most known class of biologically active molecules is the antimicrobial peptides (AMPs) that act against bacteria, fungi and protozoans. Most species begin as a free-swimming larva, breathing through gills After undergoing metamorphosis, these animals start to live in the terrestrial environment, where they breathe through lungs and through the skin. These animals start to live in the terrestrial environment, where they breathe through lungs and through the skin These adaptations are insufficient to turn amphibians completely independent of the aquatic environment. Their fragile and gelatinous eggs depend, at least, on some humidity to develop [1, 2]

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