PNAS：穴居鱼如何在食物稀缺的情况下生存

摘要 : 美国哈佛大学医学院遗传学系一项研究识别出了穴居鱼的遗传变化，这些遗传变化可能是穴居鱼发展出适应其缺乏营养物质的栖息地的代谢适应的基础。

美国哈佛大学医学院遗传学系一项研究识别出了穴居鱼的遗传变化，这些遗传变化可能是穴居鱼发展出适应其缺乏营养物质的栖息地的代谢适应的基础。生活在光合作用几乎不存在的相对昏暗的洞穴中的动物依靠腐败的动物物质、来自季节性洪水的漂浮物以及偶尔的蝙蝠粪便获得营养，它们表现出了高效的代谢，对饥饿的耐受，以及当可以获得食物的时候身体脂肪的大量储存。为了研究这种适应的遗传基础，Cliff Tabin及其同事比较了在表面生活和穴居的墨西哥丽脂鲤(Astyanax mexicanus)，结果发现穴居鱼在正常觅食的情况下比在表面生活的鱼有更大的食欲，有更多的甘油三酸酯脂肪，而且在两个月的禁食之后失去的体重最多是表面生活的鱼的体重的一半。对已知独立进化的表面生活的鱼和穴居鱼群的基因组序列的分析发现了穴居鱼的MC4R蛋白质的3个变化，这是一种与厌食症有联系的信号传导受体，这提示这种受体可能与过度进食有关。其中一个变化是该受体的甘氨酸被丝氨酸取代，而这种突变的人类对应型与肥胖有关联。基于细胞的分析揭示出了穴居鱼的MC4R的信号传导效率比含有甘氨酸的受体更低。遗传分析提示了穴居鱼的其他食欲调控基因的一个作用。这组作者说，尽管一个与MC4R有联系的临近基因可能是这些观察到的效应的基础，但该研究识别出的这个受体是穴居鱼自然选择的一个有优势的候选者。

原文链接：

Melanocortin 4 receptor mutations contribute to the adaptation of cavefish to nutrient-poor conditions

原文摘要：

Despite recent advances in the understanding of morphological evolution, the genetic underpinnings of behavioral and physiological evolution remain largely unknown. Here, we study the metabolic changes that evolved in independently derived populations of the Mexican cavefish, Astyanax mexicanus. A hallmark of cave environments is scarcity of food. Cavefish populations rely almost entirely on sporadic food input from outside of the caves. To survive under these conditions, cavefish have evolved a range of adaptations, including starvation resistance and binge eating when food becomes available. The use of these adaptive strategies differs among independently derived cave populations. Although all cavefish populations tested lose weight more slowly than their surface conspecifics during restricted rations, only a subset of cavefish populations consume more food than their surface counterparts. A candidate gene-based screen led to the identification of coding mutations in conserved residues of the melanocortin 4 receptor (MC4R) gene, contributing to the insatiable appetite found in some populations of cavefish. Intriguingly, one of the mutated residues has been shown to be linked to obesity in humans. We demonstrate that the allele results in both reduced maximal response and reduced basal activity of the receptor in vitro. We further validate in vivo that the mutated allele contributes to elevated appetite, growth, and starvation resistance. The allele appears to be fixed in cave populations in which the overeating phenotype is present. The presence of the same allele in multiple caves appears to be due to selection from standing genetic variation present in surface populations.

doi: 10.1073/PNAS.1510802112

作者：Ariel C Aspiras

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