A novel role for Mc1r in the parallel evolution of depigmentation in independent populations of the cavefish Astyanax mexicanus.
A novel role for Mc1r in the parallel evolution of depigmentation in independent populations of the cavefish Astyanax mexicanus.
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DOI：
10.1371/journal.pgen.1000326
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发表时间：
2009-01
期刊：
影响因子：
4.5
通讯作者：
Tabin CJ
中科院分区：
文献类型：
--
作者：
Gross JB;Borowsky R;Tabin CJ
简并特征的演变仍然是一个人们知之甚少的现象。直到最近才通过使用遗传分析来识别退化表型的突变。专注于墨西哥洞穴四Astyanax mexicanus，我们描述，在这里，分析的棕色突变，这是第一次在文献中描述了近40年前。这种表型导致黑色素含量减少，黑色素细胞数量减少，并在收敛洞穴型的A。墨西哥人杂交证明来自两个独立洞穴种群的F2个体中棕色表型的非互补性：Pachón和链接的Yerbaniz和Japonés洞穴，表明相同的基因座是这些鱼色素沉着减少的原因。虽然棕色突变表型在Pachón洞穴个体的白化病固定之前出现，但尚不清楚棕色突变是在Yerbaniz/Japonés洞穴的白化病固定之前还是之后出现的。使用QTL的方法结合序列和功能分析，我们发现，两个不同的基因的编码序列中的基因Mc 1 r的遗传改变导致减少色素沉着与棕色突变体表型在这些洞穴。我们的分析确定了一个新的作用，Mc 1 r的退化表型在盲目的墨西哥洞穴鱼的演变。此外，棕色表型在地理上独立的洞穴中独立出现，通过同一基因的不同突变介导。这个平行的例子表明，在洞穴适应物种的退化表型的重复进化中，某些基因是突变的频繁目标。在《物种起源》出版150周年之际，理解进化变化背后的遗传结构仍然是一个重要的挑战。当一个生物体进入一个全新的环境或生态位时，某些特征不再是生存所必需的，而其他新的特征则成为维持适应性的关键。洞穴动物就是这种转变的一个例子。许多不同的分类群（例如，甲壳类动物、蝾螈、鱼类）已经在洞穴中定居，可能是为了逃避捕食或将种群扩大到未开发的生态位。引人注目的是，尽管这些生物体之间存在显着的系统发育距离，但相似的特征却趋同进化。洞穴提供了一个独特的环境，包括没有光，很少的捕食者，很少的食物来源等，在这些条件下，一个观察到惊人的形态变化，包括减少眼睛，扩大非视觉感官系统，以及一套代谢和行为的变化。为了了解这些变化的遗传基础，我们建立了一种盲的墨西哥洞穴四头脂鲤A。墨西哥作为一个遗传系统在本文中，我们使用这个系统来研究这些动物的一个经典形态学特征，脱色。我们确定基因Mc 1 r负责减少多个洞穴中的黑色素含量。
The evolution of degenerate characteristics remains a poorly understood phenomenon. Only recently has the identification of mutations underlying regressive phenotypes become accessible through the use of genetic analyses. Focusing on the Mexican cave tetra Astyanax mexicanus, we describe, here, an analysis of the brown mutation, which was first described in the literature nearly 40 years ago. This phenotype causes reduced melanin content, decreased melanophore number, and brownish eyes in convergent cave forms of A. mexicanus. Crosses demonstrate non-complementation of the brown phenotype in F2 individuals derived from two independent cave populations: Pachón and the linked Yerbaniz and Japonés caves, indicating the same locus is responsible for reduced pigmentation in these fish. While the brown mutant phenotype arose prior to the fixation of albinism in Pachón cave individuals, it is unclear whether the brown mutation arose before or after the fixation of albinism in the linked Yerbaniz/Japonés caves. Using a QTL approach combined with sequence and functional analyses, we have discovered that two distinct genetic alterations in the coding sequence of the gene Mc1r cause reduced pigmentation associated with the brown mutant phenotype in these caves. Our analysis identifies a novel role for Mc1r in the evolution of degenerative phenotypes in blind Mexican cavefish. Further, the brown phenotype has arisen independently in geographically separate caves, mediated through different mutations of the same gene. This example of parallelism indicates that certain genes are frequent targets of mutation in the repeated evolution of regressive phenotypes in cave-adapted species. As we approach the 150th year since publication of On the Origin of Species, understanding the genetic architecture underlying evolutionary change remains an important challenge. When an organism enters a completely new environment or ecological niche, certain traits are no longer necessary for survival, while other new traits become critical for maintaining fitness. An example of such a transition is provided by cave animals. Many disparate taxa (e.g., crustaceans, salamanders, fish) have colonized caves, presumably to escape predation or expand populations into an unexploited niche. Strikingly, similar traits evolve convergently despite significant phylogenetic distance between these organisms. Caves provide a unique environment including the absence of light, few predators, few sources of food, etc. Under these conditions, one observes striking changes in morphology including reduction in eyes, expansion of non-visual sensory systems, and a suite of metabolic and behavioral changes. To understand the genetic underpinnings of these shifts, we have established the blind Mexican cave tetra, A. mexicanus, as a genetic system. In this paper, we use this system to investigate a classic morphological feature in these animals, depigmentation. We identify the gene Mc1r as being responsible for reduction in melanin content in multiple caves.
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