Investigating the physiological mechanisms that allow the blind cavefish Astyanax mexicanus to thrive in a low nutrient environment

项目总结 为了在独特的环境中生存，动物进化了一系列机制来最大限度地摄取食物， 能源的储存和使用。硬骨鱼Astianax micianus是一个经过验证的模型，可以用来理解 适应的遗传基础，代表了一个特别强大的系统来研究 新陈代谢。它以河流居住形式存在，并以多种独立衍生的盲眼窑洞形式存在 它们在永远的黑暗中茁壮成长，食物供应有限且罕见。河居与窑居 形态是完全相互干扰的，可以很容易地在实验室中培育出许多数量性状基因座 独特的形态、行为和生理特征。鲜为人知的是新陈代谢是如何 在低营养环境中进化，以防止长时间死亡或饥饿。肠神经 系统(ENS)是调节新陈代谢的中心，因为它协调胃肠(GI)的运动、营养 吸收，胃和胰腺分泌。我们发现有证据表明ENS的发育在 在某种程度上可能导致肠道吸收和葡萄糖动态平衡的差异。我们有 在人类ENS发育的关键基因(EDNRB、EDN3)中发现洞鱼特有的突变，以及 观察到，洞鱼大肠中的肠神经元较少，胃部搅动较频繁 收缩，蠕动波收缩频率较低。这些变化可能导致上肠道 吸收：我们发现从食物中获得的抗氧化剂类胡萝卜素在内脏脂肪中积聚。 穴居鱼的组织，但不是河鱼。ENS的功能还与葡萄糖动态平衡和GI有关 疾病常常伴随着糖尿病。有趣的是，我们发现穴居鱼的血糖水平较高 与河鱼相比，葡萄糖的清除速度更慢。为了了解这些生理差异如何可能 为了在低营养环境中提供适应优势，我们提出了以下目标：1)确定 EDNRB和EDN3等位基因对肠神经元数、胃肠动力和肠道转运的贡献，2) 检验类胡萝卜素在穴居鱼内脏脂肪组织中积累是由于 肠道吸收的优势，以及3)研究胰岛素信号在空腹血糖中的作用。 动态平衡。从我们的工作中出现的原则将使我们更好地理解新陈代谢 脊椎动物物种的变异。此外，我们的发现可能与人类健康有关：基因突变 EDNRB和EDN3与人类的无神经节细胞巨结肠有关，但人们对此知之甚少 人类类胡萝卜素生物利用度和葡萄糖动态平衡的变化与ENS功能有关。

PROJECT SUMMARY To survive in unique environments animals have evolved a host of mechanisms to maximize the intake, storage, and use of energy. The teleost fish Astyanax mexicanus is a proven model for understanding the genetic basis of adaptation and represents a particularly strong system to investigate evolutionary changes in metabolism. It exists as a river-dwelling form and multiple independently derived eyeless cave-dwelling forms that thrive in perpetual darkness with a limited and infrequent food supply. The river-dwelling and cave-dwelling forms are completely interfertile and can be easily bred in the lab to identify quantitative trait loci for numerous distinct morphological, behavioral, and physiological traits. There is little known about how metabolism has evolved in low nutrient environments to prevent death during long periods or starvation. The enteric nervous system (ENS) is central to regulating metabolism as it orchestrates gastrointestinal (GI) motility, nutrient absorption, and gastric and pancreatic secretion. We find evidence that ENS development is altered in cavefish in a way that could drive differences in intestinal absorption and glucose homeostasis. We have identified cavefish-specific mutations in genes critical for ENS development in humans (EDNRB, EDN3), and have observed that cavefish have fewer enteric neurons in the large intestine, more frequent stomach churning contractions, and less frequent peristaltic wave contractions. These changes may lead to superior intestinal absorption as we find that anti-oxidant carotenoids obtained from food accumulate in the visceral adipose tissue of cavefish, but not river fish. The function of the ENS is also linked to glucose homeostasis and GI disorders frequently accompany diabetes. Interestingly, we find that cavefish have higher blood glucose levels and slower glucose clearance compared to river fish. To understand how these physiological differences may provide an adaptive advantage in a low nutrient environment, we propose the following aims: 1) Determine the contribution of EDNRB and EDN3 alleles to enteric neuron number, GI motility, and bowel transit, 2) To test the hypothesis that accumulation of carotenoids in cavefish visceral adipose tissue is due to superior intestinal absorption, and 3) Investigate the role of insulin signaling in cavefish glucose homeostasis. The principles that emerge from our work will lead to a better understanding of metabolic variation in vertebrate species. Furthermore, our findings may have relevance to human health: mutations in EDNRB and EDN3 are associated with aganglionic megacolon in humans, and there is little known about how human variation in carotenoid bioavailability and glucose homeostasis are linked to ENS function.