Euryhaline Mozambique tilapia (Oreochromis mossambicus) are native to estuaries where they encounter tidal fluctuations in environmental salinity. These fluctuations can be dramatic, subjecting individuals to salinities characteristic of fresh water (FW < 0.5‰) and seawater (SW 35‰) within a single tidal cycle. In the current study, we reared tilapia under a tidal regimen that simulated the dynamic conditions of their native habitat. Tilapia were sampled every 3 h over a 24 h period to temporally resolve how prolactin (PRL) signaling is modulated in parallel with genes encoding branchial effectors of osmoregulation. The following parameters were measured: plasma osmolality, plasma PRL177 and PRL188 concentrations, pituitary prl177 and prl188 gene expression, and branchial prl receptor (prlr1 and prlr2), Na+/Cl−-cotransporter (ncc2), Na+/K+/2Cl−-cotransporter (nkcc1a), Na+/K+-ATPase (nkaα1a and nkaα1b), cystic fibrosis transmembrane regulator (cftr), and aquaporin 3 (aqp3) gene expression. Throughout the 24 h sampling period, plasma osmolality reflected whether tilapia were sampled during the FW or SW phases of the tidal cycle, whereas pituitary prl gene expression and plasma PRL levels remained stable. Branchial patterns of ncc2, nkcc1a, nkaα1a, nkaα1b, cftr, and aqp3 gene expression indicated that fish exposed to tidally changing salinities regulate the expression of these gene transcripts in a similar fashion as fish held under static SW conditions. By contrast, branchial prlr1 and prlr2 levels were highly labile throughout the tidal cycle. We conclude that local (branchial) regulation of endocrine signaling underlies the capacity of euryhaline fishes, such as Mozambique tilapia, to thrive under dynamic salinity conditions.

中文翻译：

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潮汐周期中硬骨鱼的全身催乳素信号与组织水平催乳素信号

广盐莫桑比克罗非鱼（Oreochromis mossambicus）原产于河口，在那里它们会遇到环境盐度的潮汐波动。这些波动可能是剧烈的，使个体在单个潮汐周期内遭受淡水（FW < 0.5‰）和海水（SW 35‰）的盐度特征。在目前的研究中，我们在模拟其原生栖息地动态条件的潮汐方案下饲养罗非鱼。在 24 小时内每 3 小时对罗非鱼进行一次采样，以暂时解决催乳素 (PRL) 信号如何与编码渗透调节的鳃效应器的基因平行进行调制。测量了以下参数：血浆渗透压、血浆 PRL177 和 PRL188 浓度、垂体 prl177 和 prl188 基因表达、鳃 prl 受体（prlr1 和 prlr2）、Na+/Cl--协同转运蛋白（ncc2）、Na+/K+/2Cl--协同转运蛋白 (nkcc1a)、Na+/K+-ATP 酶 (nkaα1a 和 nkaα1b)、囊性纤维化跨膜调节因子 (cftr) 和水通道蛋白 3 (aqp3) 基因表达。在整个 24 小时采样期间，血浆渗透压反映了罗非鱼是在潮汐周期的 FW 阶段还是 SW 阶段采样的，而垂体 prl 基因表达和血浆 PRL 水平保持稳定。ncc2、nkcc1a、nkaα1a、nkaα1b、cftr 和 aqp3 基因表达的鳃模式表明，暴露于潮汐变化的盐度的鱼以与静态 SW 条件下的鱼相似的方式调节这些基因转录物的表达。相比之下，鳃 prlr1 和 prlr2 水平在整个潮汐周期中高度不稳定。我们得出结论，内分泌信号的局部（分支）调节是广盐鱼类能力的基础，