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Abstract：
The troglomorphic phenotype shared by diverse cave-dwelling animals is regarded as a classical example of convergent evolution. One unresolved question is whether the characteristic eye loss in diverse cave species is based on interference with the same genetic program. Phreatichthys andruzzii, a Somalian cavefish, has evolved under constant conditions in complete darkness and shows severe troglomorphic characteristics, such as complete loss of eyes, pigments and scales. During early embryonic development, a complete eye is formed but is subsequently lost. In Astyanax mexicanus, another blind cavefish, eye loss has been attributed to interference during eye field patterning. To address whether similar pathways have been targeted by evolution independently, we investigated the retinal development of P. andruzzii, studying the expression of marker genes involved in eye patterning, morphogenesis, differentiation and maintenance. In contrast to Astyanax, patterning of the eye field and evagination of the optic vesicles proceeds without obvious deviation. However, the subsequent differentiation of retinal cell types is arrested during generation of the first-born cell type, retinal ganglion cells, which also fail to project correctly to the optic tectum. Eye degeneration in both species is driven by progressive apoptosis. However, it is retinal apoptosis in Phreatichthys that progresses in a wave-like manner and eliminates progenitor cells that fail to differentiate, in contrast to Astyanax, where lens apoptosis appears to serve as a driving force. Thus, evolution has targeted late retinal differentiation events, indicating that there are several ways to discontinue the development and maintenance of an eye.
摘要：
不同的洞穴动物共有的向后表型被认为是趋同进化的经典例子。一个未解决的问题是，不同洞穴物种的特征性眼球丧失是否基于对相同遗传程序的干扰。Phreatichthysandruzzii,一种索马里洞穴鱼，在完全黑暗的恒定条件下进化，并显示出严重的斜轨特征，比如完全失明，颜料和鳞片。在早期胚胎发育过程中,一个完整的眼睛形成，但随后丢失。在墨西哥Astyanax，另一个盲目的洞穴鱼，眼睛损失已归因于眼场图案化期间的干扰。为了解决类似的途径是否被进化独立地靶向，我们调查了andruzzii的视网膜发育，研究与眼睛模式有关的标记基因的表达，形态发生,区分和维护。与Astyanax相比，眼场的图案化和光学囊泡的逃避没有明显的偏差。然而,视网膜细胞类型的随后分化在第一出生细胞类型的生成过程中被阻止，视网膜神经节细胞,也不能正确地投射到光学构造。两个物种的眼睛退化都是由进行性凋亡驱动的。然而,它是视网膜细胞凋亡在Phreatichthys，以波浪状的方式发展，并消除未能分化的祖细胞，与Astyanax相比，晶状体凋亡似乎是一种驱动力。因此，进化的目标是晚期视网膜分化事件，表明有几种方法可以停止眼睛的开发和维护。
