Department of Biochemistry and Microbiology, University of Victoria, 3800 Finnerty Road, Victoria, British Columbia V8P 5C2, Canada.
Department of Biochemistry and Microbiology, University of Victoria, 3800 Finnerty Road, Victoria, British Columbia V8P 5C2, Canada.
Gen Comp Endocrinol. 2022 Jul 1;323-324:114047. doi: 10.1016/j.ygcen.2022.114047. Epub 2022 Apr 23.
Thyroid hormone (TH) is a critical signalling molecule for all vertebrate organisms, playing a crucial role in postembryonic development. The best-studied mechanism of TH response is through modulating gene expression, however TH's involvement in coordinating the early steps in the TH signal transduction pathway is still poorly understood. The American bullfrog, Rana [Lithobates] catesbeiana, is a useful model to study these early responses as tadpole post-embryonic development in the form of metamorphosis of the tadpole into a frog can be experimentally induced by TH exposure. The rate of TH-induced metamorphosis can be modulated by temperature where sufficiently cold temperatures (5 °C) completely halt precocious metamorphosis. Interestingly, when premetamorphic tadpoles exposed to exogenous THs at 5 °C are shifted to permissive temperatures (24 °C), their metamorphic rate exceeds that of TH-exposed tadpoles at the permissive temperature. This suggests that a molecular memory of TH exposure is retained at 5 °C even after THs are cleared at this low temperature. However, the molecular memory machinery is poorly understood. Herein we use RNA-seq analysis to identify potential components of the molecular memory in cultured tail fin that allows for the recapitulation of the molecular memory phenomenon. Eighty-one gene transcripts were TH-responsive at 5 °C compared to matched controls indicating that the molecular memory is more complex than previously thought. Many of these transcripts encode transcription factors including thyroid hormone-induced B/Zip, thibz, and a novel krüppel-like factor family member, klfX. Actinomycin D and cycloheximide treatment had no effect on their TH induction suggesting that a change in transcription or translation is not required. Rather a change in RNA stability may be a possible mechanism contributing to the molecular memory. The ability to manipulate temperature and TH response in cultured organs provide an exciting opportunity to further elucidate the early TH signalling mechanisms during postembryonic development.
甲状腺激素（TH）是所有脊椎动物的关键信号分子，在胚胎后发育中发挥着至关重要的作用。TH 反应的最佳研究机制是通过调节基因表达，然而，TH 在协调 TH 信号转导途径的早期步骤中的作用仍知之甚少。美洲牛蛙，Rana [Lithobates] catesbeiana，是研究这些早期反应的有用模型，因为通过暴露于 TH 可以实验诱导蝌蚪的胚胎后发育形式的变态。TH 诱导的变态率可以通过温度来调节，足够低的温度（5°C）可以完全阻止早熟的变态。有趣的是，当处于预变态期的蝌蚪在 5°C 下暴露于外源性 THs 时，转移到允许的温度（24°C），它们的变态率超过了在允许温度下暴露于 TH 的蝌蚪。这表明，即使在低温下清除 TH 后，在 5°C 下暴露于 TH 的分子记忆仍被保留。然而，分子记忆机制仍知之甚少。在此，我们使用 RNA-seq 分析来鉴定培养的尾鳍中分子记忆的潜在成分，这些成分允许重现分子记忆现象。与匹配的对照相比，81 个基因转录本在 5°C 时对 TH 有反应，这表明分子记忆比以前想象的更复杂。这些转录本中的许多编码转录因子，包括甲状腺激素诱导的 B/Zip、thibz 和一种新的 Krüppel 样因子家族成员 klfX。放线菌素 D 和环己酰亚胺处理对它们的 TH 诱导没有影响，这表明不需要转录或翻译的变化。相反，RNA 稳定性的变化可能是导致分子记忆的一种可能机制。在培养器官中操纵温度和 TH 反应的能力为进一步阐明胚胎后发育过程中早期 TH 信号机制提供了一个令人兴奋的机会。
