Graduate School of Agricultural and Life Sciences, the University of Tokyo, Bunkyo, Tokyo 113-8657, Japan.
Freshwater Fisheries Research Center, Chinese Academy of Fishery Sciences, Wuxi City, Jiangsu Province 214081, China.
Gene. 2021 Jan 30;767:145285. doi: 10.1016/j.gene.2020.145285. Epub 2020 Nov 2.
The genus Takifugu is a group of approximately 20 species of puffer fishes living in a wide range of salinity environments around East Asian countries. This group presents a broad spectrum of evolutionary stages adapted to anadromy as a result of speciation that occurred a short time (2-5 million years) ago on an evolutionary timescale. This group thus can be considered as a model for studying the evolutionary mechanisms of anadromy. We firstly conducted a transfer experiment from seawater to low-salinity waters on five Takifugu species: two anadromous species T. obscurus and T. ocellatus, two euryhaline wanderer marine species T. rubripes and T. niphobles, and a strictly marine species T. snyderi, and confirmed that the capacity for acclimation to hypotonic environments was associated with their life history strategies. Next, transcriptomes of the gill and intestine of these species in hypotonic condition were compared to those under hypertonic condition for each species using RNA-Sequencing so as to determine possible candidate transporters playing an important role on freshwater adaptation. As this analysis suggested that cftr, encoding an important ion transporter for seawater acclimation in the gill, and ncc, encoding a transporter that is suggested to play important osmoregulatory roles in the intestine, are important candidates, their expression was validated by quantitative real-time PCR analysis. Expression of cftr was downregulated in the gills of the four euryhaline species under the hypotonic condition, but no change was detected in the gill of stenohaline T. snyderi, which may be one reason for the poor hypotonic acclimation capacity of T. snyderi. Expression of ncc was clearly upregulated in the intestines of the two anadromous species under the hypotonic condition, but not in other three species. Different ion transporter expression patterns between the five species indicate that the transcriptional regulation of cftr in the gill and ncc in the intestine may be important for the improvement of hypotonic acclimation capacity and evolution of anadromy in the Takifugu species.
箱鲀属是一个约有 20 种的东方鱼类种群，生活在东亚国家周围广泛的盐度环境中。由于在进化时间尺度上，2-500 万年前发生了物种形成，该种群呈现出广泛的适应洄游的进化阶段。因此，该种群可以被视为研究洄游进化机制的模型。我们首先在五个箱鲀物种上进行了从海水到低盐度水域的转移实验：两种洄游物种暗纹东方鲀和红鳍东方鲀，两种广盐性洄游海洋物种红鳍东方鲀和黄鳍东方鲀，以及一种严格的海洋物种红鳍东方鲀。并证实了适应低渗环境的能力与它们的生活史策略有关。接下来，我们使用 RNA 测序比较了这些物种在低渗条件下和高渗条件下的鳃和肠转录组，以确定可能在淡水适应中起重要作用的候选转运蛋白。由于该分析表明，cftr 编码了鳃中适应海水的重要离子转运蛋白，ncc 编码了在肠中可能发挥重要渗透调节作用的转运蛋白，因此它们是重要的候选蛋白，我们通过定量实时 PCR 分析验证了它们的表达。cftr 在四种广盐性物种的低渗条件下的鳃中表达下调，但在狭盐性的红鳍东方鲀的鳃中未检测到变化，这可能是红鳍东方鲀低渗适应能力差的原因之一。ncc 在两种洄游性物种的低渗条件下的肠中表达明显上调，但在其他三种物种中没有上调。这五种箱鲀物种之间不同的离子转运蛋白表达模式表明，cftr 在鳃中的转录调控和 ncc 在肠中的转录调控可能对提高低渗适应能力和箱鲀属物种的洄游进化很重要。
