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Reduced effects of thyroid hormone on gene expression and metamorphosis in a paedomorphic plethodontid salamander
Author(s) -
Aran Robert P.,
Steffen Michael A.,
Martin Samuel D.,
Lopez Olivia I.,
Bonett Ronald M.
Publication year - 2014
Publication title -
journal of experimental zoology part b: molecular and developmental evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.823
H-Index - 63
eISSN - 1552-5015
pISSN - 1552-5007
DOI - 10.1002/jez.b.22580
Subject(s) - salamander , neoteny , metamorphosis , thyroid , biology , salamandridae , hormone , gene , expression (computer science) , gene expression , endocrinology , medicine , caudata , zoology , ecology , larva , genetics , computer science , programming language
It has been over a century since Gudernatsch (1912, Wilhelm Roux Arch Entwickl Mech Org 35:457–483) demonstrated that mammalian thyroid gland extracts can stimulate tadpole metamorphosis. Despite the tremendous developmental diversity of amphibians, mechanisms of metamorphosis have mostly been studied in a few model systems. This limits our understanding of the processes that influence the evolution of developmental aberrations. Here we isolated thyroid hormone receptors alpha (TRα) and beta (TRβ) from Oklahoma salamanders ( Eurycea tynerensis ), which exhibit permanently aquatic (paedomorphic) or biphasic (metamorphic) developmental modes in different populations. We found that TRα and TRβ were upregulated by thyroid hormone (T 3 ) in tail tissues of larvae from metamorphic populations, but basal levels of TR expression and T 3 responsiveness were reduced in larvae from paedomorphic populations. Likewise, we found that T 3 treatment resulted in complete loss of larval epibranchials in larvae from metamorphic populations, but little to no epibranchial remodeling occurred in larvae from paedomorphic populations over the same duration. This is the first study to directly demonstrate reduced gene expression and metamorphic responses to T 3 in a paedomorphic plethodontid compared to metamorphic conspecifics, and the first salamander system to show differential expression of thyroid hormone receptors associated with alternative developmental patterns. J. Exp. Zool. (Mol. Dev. Evol.) 322B: 294–303, 2014 . © 2014 Wiley Periodicals, Inc.