Irachi Shotaro, Hall Daniel J, Fleming Mitchell S, Maugars Gersende, Björnsson Björn Thrandur, Dufour Sylvie, Uchida Katsuhisa, McCormick Stephen D
U.S. Geological Survey, Leetown Science Center, Conte Anadromous Fish Research Laboratory, Turners Falls, MA, USA; Graduate School of Agriculture, University of Miyazaki, 1-1 Gakuen-kibanadai Nishi, Miyazaki, 889-2192, Japan.
U.S. Geological Survey, Leetown Science Center, Conte Anadromous Fish Research Laboratory, Turners Falls, MA, USA.
Mol Cell Endocrinol. 2021 Jan 1;519:111056. doi: 10.1016/j.mce.2020.111056. Epub 2020 Oct 15.
Seasonal timing is important for many critical life history events of vertebrates, and photoperiod is often used as a reliable seasonal cue. In mammals and birds, it has been established that a photoperiod-driven seasonal clock resides in the brain and pituitary, and is driven by increased levels of pituitary thyroid stimulating hormone (TSH) and brain type 2 iodothyronine deiodinase (DIO2), which leads to local increases in triiodothyronine (T). In order to determine if a similar mechanism occurs in fish, we conducted photoperiod manipulations in anadromous (migratory) Atlantic salmon (Salmo salar) that use photoperiod to time the preparatory development of salinity tolerance which accompanies downstream migration in spring. Changing daylength from short days (light:dark (LD) 10:14) to long days (LD 16:8) for 20 days increased gill Na/K-ATPase (NKA) activity, gill NKAα1b abundance and plasma growth hormone (GH) levels that normally accompany increased salinity tolerance of salmon in spring. Long-day exposure resulted in five-fold increases in pituitary tshβb mRNA levels after 10 days and were sustained for at least 20 days. tshβb mRNA levels in the saccus vasculosus were low and not influenced by photoperiod. Increased daylength resulted in significant increases in dio2b mRNA levels in the hypothalamus and midbrain/optic tectum regions of the brain. The results are consistent with the presence of a photoperiod-driven seasonal clock in fish which involves pituitary TSH, brain DIO2 and the subsequent production of T, supporting the hypothesis that this is a common feature of photoperiodic regulation of seasonality in vertebrates.
季节性定时对脊椎动物许多关键的生活史事件都很重要，光周期常被用作可靠的季节性线索。在哺乳动物和鸟类中，已经确定光周期驱动的季节性时钟存在于大脑和垂体中，并且由垂体促甲状腺激素（TSH）和脑型2碘甲状腺原氨酸脱碘酶（DIO2）水平的升高驱动，这会导致局部三碘甲状腺原氨酸（T）水平升高。为了确定鱼类是否存在类似机制，我们对溯河洄游（洄游性）的大西洋鲑（Salmo salar）进行了光周期操作，这种鱼利用光周期来确定耐盐性的准备性发育时间，而耐盐性的发育与春季下游洄游相伴。将日照长度从短日照（光照：黑暗（LD）10:14）改为长日照（LD 16:8）持续20天，会增加鳃Na/K-ATP酶（NKA）活性、鳃NKAα1b丰度以及血浆生长激素（GH）水平，而这些通常伴随着春季鲑鱼耐盐性的提高。长日照暴露10天后，垂体tshβb mRNA水平增加了五倍，并至少持续20天。血管囊中的tshβb mRNA水平较低，且不受光周期影响。日照长度增加导致大脑下丘脑和中脑/视顶盖区域的dio2b mRNA水平显著增加。这些结果与鱼类中存在光周期驱动的季节性时钟一致，该时钟涉及垂体TSH、脑DIO2以及随后T的产生，支持了这是脊椎动物季节性光周期调节的一个共同特征这一假设。
