Alunni Alessandro, Menuet Arnaud, Candal Eva, Pénigault Jean-Baptiste, Jeffery William R, Rétaux Sylvie
MSNC INRA Group, Institut de Neurobiologie Alfred Fessard, Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette, France.
J Comp Neurol. 2007 Nov 10;505(2):221-33. doi: 10.1002/cne.21488.
The sighted surface-dwelling (surface fish, SF) and the blind cave-living (cavefish, CF) forms of Astyanax mexicanus offer a unique opportunity to study the evolutionary changes in developmental mechanisms that lead to retinal degeneration. Previous data have shown the role of increased midline Sonic Hedgehog (Shh) signalling in cavefish eye degeneration (Yamamoto et al. [2004] Nature 431:844-847). Here, we have compared the major steps of eye development in SF and CF between 14 hours and 5 days of development. We have analyzed cell proliferation through PCNA and phospho-histone H3 staining and apoptosis through TUNEL and live LysoTracker analysis. We have assessed the expression of the major eye development signalling factors Shh and Fgf8, and the eye patterning genes Pax6, Lhx2, Lhx9, and Vax1, together with the differentiation marker GAD65. We show that eye development is retarded in CF and that cell proliferation in CF retina is proportionately similar to SF during early development, yet the retina degenerates after massive apoptosis in the lens and widespread cell death throughout the neuroretina. Moreover, and surprisingly, the signalling, patterning, and differentiation processes leading to the establishment of retinal layers and cell types happen almost normally in CF, although some signs of disorganization, slight heterochronies, and a lack of expression gradients are observable. Our data demonstrate that the evolutionary process of eye degeneration in the blind CF does not occur because of patterning defects of the retina and are consistent with the proposed scenario in which the trigger for eye degeneration in CF is lens apoptosis.
墨西哥丽脂鲤的有视力的表层栖息型（表层鱼，SF）和盲眼的洞穴栖息型（洞穴鱼，CF）为研究导致视网膜退化的发育机制的进化变化提供了独特的机会。先前的数据表明，中线音猬因子（Shh）信号增强在洞穴鱼眼睛退化中起作用（山本等人，[2004]《自然》431:844 - 847）。在这里，我们比较了发育14小时至5天期间SF和CF眼睛发育的主要步骤。我们通过增殖细胞核抗原（PCNA）和磷酸化组蛋白H3染色分析细胞增殖，通过末端脱氧核苷酸转移酶介导的缺口末端标记（TUNEL）和活细胞溶酶体追踪分析（LysoTracker）分析细胞凋亡。我们评估了主要的眼睛发育信号因子Shh和Fgf8、眼睛模式形成基因Pax6、Lhx2、Lhx9和Vax1的表达，以及分化标志物谷氨酸脱羧酶65（GAD65）的表达。我们发现CF的眼睛发育迟缓，并且CF视网膜中的细胞增殖在早期发育阶段与SF成比例地相似，但在晶状体大量凋亡和整个神经视网膜广泛细胞死亡后，视网膜发生退化。此外，令人惊讶的是，尽管可以观察到一些组织紊乱、轻微异时性和缺乏表达梯度的迹象，但导致视网膜层和细胞类型建立的信号传导、模式形成和分化过程在CF中几乎正常发生。我们的数据表明，盲眼CF中眼睛退化的进化过程并非由于视网膜模式形成缺陷导致，并且与所提出的CF眼睛退化触发因素是晶状体凋亡的设想一致。
