Adaptations to Counter Diffusional Constraints in Muscle of Channichthyid Icefishes

南极鱼类物种在4000万年来在几乎恒定的0摄氏度左右的体温下进化，暴露在长期寒冷中需要适应，以克服细胞过程的热敏感性，并允许保留在较温暖的体温下会致命的特征。这些特征将在这个专注于无血红蛋白冰鱼家族的项目中得到解决。虽然众所周知，这些冰鱼缺乏血红蛋白，细胞内呼吸色素的存在/不存在，肌红蛋白的存在/不存在还没有被认为是一个家族特征。初步证据表明，肌红蛋白仅在单一种类的冰鱼的一个组织中表达。这一结论的有效性将通过免疫学方法进行验证，以确定肌红蛋白是否在通道类物种的氧化肌肉中表达。还将确定肌红蛋白基因蛋白编码序列的点突变是否导致在表达/不表达肌红蛋白的组织中缺乏该蛋白的表达mRNA。本课程将研究细胞内脂肪酸结合蛋白在低温下发挥作用所必需的蛋白质结构特征；这种蛋白质可增强代谢重要脂肪酸的跨细胞运动，并起到细胞保护的作用。对冰鱼糖酵解肌肉的超微结构和生物化学的协调测量将确定在冰鱼组织中发生的适应。这些实验将测试提出的范式，即克服扩散限制的适应是确保低温细胞温度下生命的根本。这些研究将增加对高等脊椎动物肌肉适应反应的洞察，并增加对南极鱼类新陈代谢的了解，南极鱼类是对南大洋营养结构重要的一类。

Antarctic fish species have evolved over 40 million years at nearly constant body temperatures of about 0 C. Exposure to chronic cold has required adaptations to overcome thermal sensitivities of cellular processes and to permit retention of characteristics that would be lethal at warmer body temperatures. Such features will be addressed in this project which focuses on a hemoglobinless icefish family. Although it is well established that these icefishes lack hemoglobin, the presence/absence of the intracellular respiratory pigment, myoglobin has not been resolved as a familial characteristic. Preliminary evidence is presented that suggests myoglobin is expressed exclusively in one tissue of a single icefish species. Validity of this conclusion will be tested using immunological methods to establish definitively whether myoglobin is expressed in oxidative muscles of channichthyid species. It will also be determined whether point mutations in the protein encoding sequence of the myoglobin gene account for lack of the protein's expression mRNA in tissues that do/do not express myoglobin. Characteristics in protein structure that are necessary for function of the intracellular fatty acid binding protein at cold cell temperatures will be examined; this protein enhances transcellular movement of metabolically important fatty acids and serves a cytoprotectant function. Coordinated ultrastructural and biochemical measurements of icefish glycolytic muscle will identify adaptations that have occurred in the tissues of icefish. These experiments will test the proposed paradigm that adaptations to overcome diffusional limitations are fundamental to ensure life at cold cellular temperatures. The studies will add insight into adaptive responses of muscle in higher vertebrates and increase understanding of the metabolism of antarctic fishes, a group important to the trophic structure of the Southern Ocean.