Austin Hammond S, Jackman Kevin W, Partovi Shireen H, Veldhoen Nik, Helbing Caren C
Department of Biochemistry and Microbiology, University of Victoria, P.O. Box 1700, STN CSC, Victoria, BC, V8W 2Y2, Canada.
Department of Biochemistry and Microbiology, University of Victoria, P.O. Box 1700, STN CSC, Victoria, BC, V8W 2Y2, Canada.
Comp Biochem Physiol Part D Genomics Proteomics. 2016 Mar;17:58-65. doi: 10.1016/j.cbd.2016.01.002. Epub 2016 Jan 7.
Environmental temperature modulates thyroid hormone (TH)-dependent metamorphosis in some amphibian species. The North American bullfrog--Rana (Lithobates) catesbeiana - tadpole is naturally adapted to a wide range of temperatures over multiple seasons. Cold temperatures delay while warmer temperatures accelerate metamorphosis. Exogenous TH exposure of premetamorphic tadpoles results in a rapid precocious induction of metamorphosis at warm temperatures (20-25 °C). The same exposure at cold temperatures (4-5 °C) does not elicit an overt metamorphic response. However, a molecular memory of TH exposure is established such that cold, TH-exposed tadpoles returned to permissive warm temperatures will rapidly execute TH-induced genetic programs. Previous mRNA profiling has identified TH-regulated transcription factors encoded by thra, thrb, thibz, klf9, and cebp1 as components of the molecular memory after one week post-exposure. However, a further hierarchy may exist within the initiation phase since many gene transcripts demonstrated tissue-specific patterns. Whether the molecular memory is organ autonomous or requires additional modulating factors is unknown. Herein we examine tail fin and back skin and determine that thibz is the only transcript that is TH-responsive after 2 days post-exposure at low temperature in both tissues in the intact animal. In back skin, cebp1 is also TH-responsive under these conditions. Serum-free tail fin organ culture (C-Fin) reveals that the thibz response is organ autonomous whereas cultured back skin (C-Skin) results suggest that thibz and cebp1 require an additional factor for induction from elsewhere within the intact animal. Subsequent investigations are now possible to identify endogenous factors that modulate the molecular memory in intact animals.
环境温度可调节某些两栖动物物种中甲状腺激素（TH）依赖的变态发育。北美牛蛙——牛蛙属（石蛙属）牛蛙蝌蚪能自然适应多个季节的广泛温度范围。低温会延迟变态发育，而高温则会加速变态发育。对变态前的蝌蚪进行外源性TH暴露，在温暖温度（20 - 25°C）下会导致变态发育迅速早熟诱导。在低温（4 - 5°C）下进行相同的暴露则不会引发明显的变态反应。然而，会建立TH暴露的分子记忆，使得暴露于TH的低温蝌蚪回到适宜的温暖温度时会迅速执行TH诱导的遗传程序。先前的mRNA谱分析已确定，暴露一周后，由thra、thrb、thibz、klf9和cebp1编码的TH调节转录因子是分子记忆的组成部分。然而，在起始阶段可能还存在进一步的层级关系，因为许多基因转录本表现出组织特异性模式。分子记忆是器官自主的还是需要额外的调节因子尚不清楚。在此，我们检查了尾鳍和背部皮肤，确定thibz是完整动物中两种组织在低温暴露2天后唯一对TH有反应的转录本。在背部皮肤中，cebp1在这些条件下也对TH有反应。无血清尾鳍器官培养（C - Fin）表明thibz反应是器官自主的，而培养的背部皮肤（C - Skin）结果表明thibz和cebp1需要来自完整动物其他部位的额外因子才能诱导。现在可以进行后续研究来确定调节完整动物分子记忆的内源性因子。
