Evolution of Eye Regression in Cavefish

洞穴鱼眼睛回归的进化

• 批准号: 0110275
• 负责人: William Jeffery
• 金额: $ 39万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-09-01 至 2005-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0110275&HistoricalAwards=false
• 关键词: Evolution; Eye; Regression; Cavefish

0110275JefferyLittle is known about the remarkable evolutionary changes that have occurred in cave animals. This proposal continues Dr. Jeffery's research on the evolution of eye degeneration in Astyanax mexicanus, a teleost consisting of an eyed surface form (surface fish) and numerous conspecific eyeless cave forms (cavefish). Although cavefish lack eyes as adults, they form small eye primordia during embryogenesis, which later arrest in development and degenerate. In concert with eye degeneration, more elaborate feeding and gustatory systems have evolved in cavefish. His previous grant resulted in three new discoveries. First, he showed that eye degeneration has evolved independently in some cavefish populations. Second, he showed that lens apoptosis plays a major role in eye degeneration. Accordingly, the cavefish eye can be restored by transplantation of a surface fish lens primordium into the optic cup of a cavefish embryo. Third, he showed that Pax6, a gene required for eye development, is downregulated at the anterior midline in cavefish embryos. This discovery led to the hypothesis that cavefish exhibit enhanced midline signaling, the major focus of this proposal. He now plan to test this hypothesis and the possibility that degeneration of eyes and elaboration of feeding and gustatory organs have evolved repeatedly in cavefish due to hyperactive midline signaling during embryogenesis. The first objective is to determine whether cavefish embryos show hyperactive (hedgehog and/or nodal/TGFB) signaling at the anterior midline. Preliminary evidence shows that sonic hedgehog (Shh) gene expression is enhanced at the anterior midline in a single cavefish population. The second objective is to determine whether hyperactive midline signaling and Pax6 downregulation also occur in independently evolved cavefish populations. This will indicate whether the same or different developmental mechanisms have been changed during cavefish evolution. The third objective is to determine the effect of perturbing midline signaling on Pax6 expression and eye degeneration. He will test the possibility that surface fish and cavefish eye phenotypes are interchangeable by altering the levels of midline signaling gene expression in surface fish and cavefish embryos. Preliminary results show that changes in the level of Shh expression can phenocopy surface and cavefish. Time permitting, he will also determine whether eye degeneration involves changes in the organizer of cavefish embryos and whether there is a "developmental tradeoff" eye development and enhancement of feeding and gustatory systems, thus explaining evolutionary forces resulting in the cavefish phenotype. He expects the results of this investigation to provide new insights into the mechanisms underlying an evolutionary change in morphology.

0110275Jeffery 对于洞穴动物发生的显着进化变化知之甚少。 这项提议延续了 Jeffery 博士对 Astyanax mexicanus 眼睛退化进化的研究，Astyanax mexicanus 是一种硬骨鱼，由有眼的表面形态（表层鱼）和许多同种的无眼洞穴形态（洞穴鱼）组成。 尽管穴居鱼成年后没有眼睛，但它们在胚胎发生过程中形成小眼原基，随后发育停滞并退化。 与眼睛退化相呼应，洞穴鱼进化出了更复杂的摄食和味觉系统。 他之前的资助带来了三项新发现。 首先，他表明眼睛退化在一些洞穴鱼种群中是独立进化的。 其次，他表明晶状体细胞凋亡在眼睛退化中起着重要作用。 因此，可以通过将表面鱼晶状体原基移植到洞穴鱼胚胎的视杯中来恢复洞穴鱼的眼睛。 第三，他发现 Pax6（一种眼睛发育所需的基因）在洞穴鱼胚胎的前中线处下调。 这一发现引发了这样的假设：洞穴鱼表现出增强的中线信号传导，这是该提案的主要焦点。 他现在计划检验这一假设，以及由于胚胎发生过程中中线信号过度活跃，导致洞穴鱼眼睛退化、进食和味觉器官反复进化的可能性。 第一个目标是确定洞穴鱼胚胎是否在前中线表现出过度活跃的（刺猬和/或节点/TGFB）信号传导。 初步证据表明，在单个洞穴鱼种群中，前中线的音刺猬（Shh）基因表达增强。 第二个目标是确定独立进化的洞穴鱼种群中是否也发生过度活跃的中线信号传导和 Pax6 下调。 这将表明在洞穴鱼进化过程中是否改变了相同或不同的发育机制。 第三个目标是确定扰动中线信号传导对 Pax6 表达和眼睛退化的影响。 他将通过改变表层鱼和洞穴鱼胚胎中线信号基因的表达水平来测试表层鱼和洞穴鱼眼睛表型可互换的可能性。 初步结果表明，Shh表达水平的变化可以反映地表鱼和洞穴鱼的表型。如果时间允许，他还将确定眼睛退化是否涉及洞穴鱼胚胎组织的变化，以及眼睛发育与摄食和味觉系统增强是否存在“发育权衡”，从而解释导致洞穴鱼表型的进化力量。 他预计这项研究的结果将为形态进化变化背后的机制提供新的见解。