Biology of Aquatic Organisms and Ecosystems (BOREA), Muséum National d'Histoire Naturelle, CNRS, IRD, Sorbonne Université, Université de Caen Normandie, Université des Antilles, 75231, Paris, Cedex 05, France.
Conservatoire National du Saumon Sauvage, 43300, Chanteuges, France.
Sci Rep. 2019 Mar 14;9(1):4561. doi: 10.1038/s41598-019-40019-5.
Smoltification is a metamorphic event in salmon life history, which initiates downstream migration and pre-adapts juvenile salmon for seawater entry. While a number of reports concern thyroid hormones and smoltification, few and inconclusive studies have addressed the potential role of thyrotropin (TSH). TSH is composed of a α-subunit common to gonadotropins, and a β-subunit conferring hormone specificity. We report the presence and functional divergence of duplicated TSH β-subunit paralogs (tshβa and tshβb) in Atlantic salmon. Phylogeny and synteny analyses allowed us to infer that they originated from teleost-specific whole genome duplication. Expression profiles of both paralogs in the pituitary were measured by qPCR throughout smoltification in Atlantic salmon from the endangered Loire-Allier population raised in a conservation hatchery. This revealed a striking peak of tshβb expression in April, concomitant with downstream migration initiation, while tshβa expression remained relatively constant. In situ hybridization showed two distinct pituitary cell populations, tshβa cells in the anterior adenohypophysis, and tshβb cells near to the pituitary stalk, a location comparable to the pars tuberalis TSH cells involved in seasonal physiology and behaviour in birds and mammals. Functional divergence of tshβ paralogs in Atlantic salmon supports a specific role of tshβb in smoltification.
性成熟是鲑鱼生命周期中的一种变态事件，它启动了鲑鱼的下游洄游，并使幼鲑适应了进入海水的环境。虽然有许多关于甲状腺激素和性成熟的报告，但很少有研究涉及促甲状腺激素（TSH）的潜在作用。TSH 由促性腺激素的α亚单位和赋予激素特异性的β亚单位组成。我们报告了大西洋鲑鱼中存在和功能分化的重复 TSH β亚单位基因（tshβa 和 tshβb）。通过对来自濒危的卢瓦尔-阿利埃种群的大西洋鲑鱼在性成熟过程中的垂体进行 qPCR 表达谱分析，我们推断它们起源于硬骨鱼特异性的全基因组复制。这揭示了 tshβb 表达的显著峰值出现在 4 月，与下游洄游的开始同时发生，而 tshβa 表达则相对稳定。原位杂交显示了两种不同的垂体细胞群，tshβa 细胞位于前腺垂体，而 tshβb 细胞位于垂体柄附近，这一位置与鸟类和哺乳动物中参与季节性生理和行为的脑垂体柄 TSH 细胞相似。大西洋鲑鱼中 tshβ 基因的功能分化支持 tshβb 在性成熟中的特定作用。
