Evolutionary Conservation of Thyroid Hormone Receptor and Deiodinase Expression Dynamics in ovo in a Direct-Developing Frog, Eleutherodactylus coqui
Evolutionary Conservation of Thyroid Hormone Receptor and Deiodinase Expression Dynamics in ovo in a Direct-Developing Frog, Eleutherodactylus coqui
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DOI：
10.3389/fendo.2019.00307
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发表时间：
2019-05-24
影响因子：
5.2
通讯作者：
Hanken, James
中科院分区：
文献类型：
--
作者：
Laslo, Mara;Denver, Robert J.;Hanken, James
直接发育是两栖动物的一种生殖模式，至少在十几个无脊椎动物谱系中，它独立于祖先的双相生活史进化而来。大多数直接发育的青蛙，包括波多黎各coqui， Eleutherodactylus coqui，没有自由生活的水生幼虫，而是从陆地上的卵孵化成小型的成年青蛙。它们的胚胎发育包括许多幼虫特异性特征的短暂形成和成年特异性特征的形成，这些特征通常在间接发育的青蛙的胚胎后-在变态过程中形成。我们发现，相对于间接发育的蛙类在变形过程中所观察到的，coqui肢和尾的甲状腺激素受体α (thra)和β (thrb)以及去碘酶II （dio2）和III (dio3) mrna在孵化前的发育模式是保守的。此外，thra， thrb和dio2 mrna在胚胎甲状腺形成前在肢体中表达。液相色谱质谱分析显示，母体衍生的甲状腺激素存在于胚胎发生的早期，包括胚胎产生甲状腺激素增加之前的手指形成阶段。与热带棘猴蝌蚪相比，棘猴胚胎从环境中吸收的3,5,3′-三碘甲状腺原氨酸（T-3）要少得多。然而，E. coqui组织外植体对外源T-3有强大而直接的基因表达反应，类似于在变态物种中看到的。肢体中甲状腺轴的关键成分的存在以及肢体组织对T-3的反应能力表明，甲状腺激素介导的肢体发育可能在甲状腺形成之前就开始了。在间接发育的无尾动物中，依赖甲状腺激素的肢体发育和尾巴吸收特征在进化上是保守的，但它们在卵中发生。
Direct development is a reproductive mode in amphibians that has evolved independently from the ancestral biphasic life history in at least a dozen anuran lineages. Most direct-developing frogs, including the Puerto Rican coqui, Eleutherodactylus coqui, lack a free-living aquatic larva and instead hatch from terrestrial eggs as miniature adults. Their embryonic development includes the transient formation of many larval-specific features and the formation of adult-specific features that typically form postembryonically-during metamorphosis-in indirect-developing frogs. We found that pre-hatching developmental patterns of thyroid hormone receptors alpha (thra) and beta (thrb) and deiodinases type II (dio2) and type III (dio3) mRNAs in E. coqui limb and tail are conserved relative to those seen during metamorphosis in indirect-developing frogs. Additionally, thra, thrb, and dio2 mRNAs are expressed in the limb before formation of the embryonic thyroid gland. Liquid-chromatography mass-spectrometry revealed that maternally derived thyroid hormone is present throughout early embryogenesis, including stages of digit formation that occur prior to the increase in embryonically produced thyroid hormone. Eleutherodactylus coqui embryos take up much less 3,5,3'-triiodothyronine (T-3) from the environment compared with X. tropicalis tadpoles. However, E. coqui tissue explants mount robust and direct gene expression responses to exogenous T-3 similar to those seen in metamorphosing species. The presence of key components of the thyroid axis in the limb and the ability of limb tissue to respond to T-3 suggest that thyroid hormone-mediated limb development may begin prior to thyroid gland formation. Thyroid hormone-dependent limb development and tail resorption characteristic of metamorphosis in indirect-developing anurans are evolutionarily conserved, but they occur instead in ovo in E. coqui.