The Pacific bluefin tuna (Thunnus orientalis) is a regionally endothermic fish that maintains temperatures in their swimming musculature, eyes, brain and viscera above that of the ambient water. Within their skeletal muscle, a thermal gradient exists, with deep muscles, close to the backbone, operating at elevated temperatures compared to superficial muscles near the skin. Their heart, by contrast, operates at ambient temperature, which in bluefin tunas can range widely. Cardiac function in tunas reduces in cold waters, yet the heart must continue to supply blood for metabolically demanding endothermic tissues. Physiological studies indicate Pacific bluefin tuna have an elevated cardiac capacity and increased cold-tolerance compared to warm-water tuna species, primarily enabled by increased capacity for sarcoplasmic reticulum calcium cycling within the cardiac muscles. Here, we compare tissue-specific gene-expression profiles of different cardiac and skeletal muscle tissues in Pacific bluefin tuna. There was little difference in the overall expression of calcium-cycling and cardiac contraction pathways between atrium and ventricle. However, expression of a key sarcoplasmic reticulum calcium-cycling gene, SERCA2b, which plays a key role maintaining intracellular calcium stores, was higher in atrium than ventricle. Expression of genes involved in aerobic metabolism and cardiac contraction were higher in the ventricle than atrium. The two morphologically distinct tissues that derive the ventricle, spongy and compact myocardium, had near-identical levels of gene expression. More genes had higher expression in the cool, superficial muscle than in the warm, deep muscle in both the aerobic red muscle (slow-twitch) and anaerobic white muscle (fast-twitch), suggesting thermal compensation. We find evidence of widespread transcriptomic differences between the Pacific tuna ventricle and atrium, with potentially higher rates of calcium cycling in the atrium associated with the higher expression of SERCA2b compared to the ventricle. We find no evidence that genes associated with thermogenesis are upregulated in the deep, warm muscle compared to superficial, cool muscle. Heat generation may be enabled by by the high aerobic capacity of bluefin tuna red muscle.

中文翻译：

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区域吸热鱼，太平洋蓝鳍金枪鱼，东方金枪鱼的骨骼肌和心脏转录组学。

太平洋蓝鳍金枪鱼（Thunnus Orientalis）是一种区域吸热性鱼类，其游泳肌肉，眼睛，大脑和内脏的温度保持在高于周围水温的水平。与邻近皮肤的浅层肌肉相比，在其骨骼肌内存在着一个热梯度，靠近骨骼的深层肌肉在高温下运行。相比之下，他们的心脏在室温下工作，在蓝鳍金枪鱼中，温度范围很广。在冷水中，金枪鱼的心脏功能会降低，但是心脏必须继续为需要代谢的吸热组织供应血液。生理研究表明，与温水金枪鱼品种相比，太平洋蓝鳍金枪鱼具有更高的心脏容量和更高的耐寒性，主要是由于心肌内肌浆网钙循环能力增强所致。在这里，我们比较太平洋蓝鳍金枪鱼中不同心脏和骨骼肌组织的组织特异性基因表达谱。心房和心室之间的钙循环和心脏收缩途径的总体表达几乎没有差异。然而，在维持细胞内钙存储中起关键作用的关键肌浆网钙循环基因SERCA2b的表达在心房中高于心室。涉及有氧代谢和心脏收缩的基因的表达在心室中高于心房。衍生出心室，海绵状和致密心肌的两种形态上截然不同的组织的基因表达水平几乎相同。有氧红色肌肉（慢肌）和厌氧白色肌肉（快肌）中，在凉爽的浅层肌肉中比在温暖的深层肌肉中表达更多的基因，这表明存在热补偿。我们发现，太平洋金枪鱼心室和心房之间存在广泛的转录组差异，与心室相比，SERCA2b的较高表达可能导致心房中钙循环的速率更高。我们发现没有证据表明与深层热肌肉相比，深层热肌肉中与生热相关的基因被上调。蓝鳍金枪鱼红色肌肉的高有氧能力可以促进热量的产生。建议进行热补偿。我们发现，太平洋金枪鱼心室和心房之间存在广泛的转录组差异，与心室相比，SERCA2b的较高表达可能导致心房中钙循环的速率更高。我们发现没有证据表明，与深层热肌肉相比，深层热肌肉中与生热相关的基因被上调。蓝鳍金枪鱼红色肌肉的高有氧能力可能会产生热量。建议进行热补偿。我们发现，太平洋金枪鱼心室和心房之间存在广泛的转录组差异，与心室相比，SERCA2b的较高表达可能导致心房中钙循环的速率更高。我们发现没有证据表明，与深层热肌肉相比，深层热肌肉中与生热相关的基因被上调。蓝鳍金枪鱼红色肌肉的高有氧能力可以促进热量的产生。温暖的肌肉相比肤浅的肌肉。蓝鳍金枪鱼红色肌肉的高有氧能力可能会产生热量。温暖的肌肉相比肤浅的肌肉。蓝鳍金枪鱼红色肌肉的高有氧能力可能会产生热量。