5 years ago

Thyroid hormone receptor α- and β-knockout Xenopus tropicalis tadpoles reveal subtype-specific roles during development.

Yoshio Yaoita, Keisuke Nakajima, Ichiro Tazawa
Thyroid hormone (TH) binds TH receptor alpha (TRα) and beta (TRβ) receptors to induce amphibian metamorphosis. Whereas TH signalling has been well studied, functional differences between TRα and TRβ during this process have not been characterized. To understand how each TR contributes to metamorphosis, we generated TRα- and TRβ-knockout tadpoles of Xenopus tropicalis and examined developmental abnormalities, histology of the tail and intestine, and mRNA expression of genes encoding extracellular matrix (ECM)-degrading enzymes. In TRβ-knockout tadpoles, tail regression was delayed significantly and a healthy notochord was observed even 5 days after the initiation of tail shortening (stage 62), whereas in the tails of wild-type and TRα-knockout tadpoles, notochord disappeared after approximately 1 day. The mRNA expression levels of genes encoding ECM-degrading enzymes (MMP2, MMP9TH, MMP13, MMP14, and FAPα) were obviously reduced in the tail tip of TRβ-knockout tadpoles, with the shortening tail. The reduction in olfactory nerve length and head narrowing by gill absorption were also affected. Hind limb growth and intestinal shortening were not compromised in TRβ-knockout tadpoles, whereas tail regression and olfactory nerve shortening appeared to proceed normally in TRα-knockout tadpoles, except for the precocious development of hind limbs. Our results demonstrated the distinct roles of TRα and TRβ in hind limb growth and tail regression, respectively.

Publisher URL: http://doi.org/10.1210/en.2017-00601

DOI: 10.1210/en.2017-00601

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