Molecular analysis of the amphioxus frontal eye unravels the evolutionary origin of the retina and pigment cells of the vertebrate eye
Molecular analysis of the amphioxus frontal eye unravels the evolutionary origin of the retina and pigment cells of the vertebrate eye
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DOI：
10.1073/pnas.1207580109
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发表时间：
2012-09
期刊：
影响因子：
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通讯作者：
Pavel Vopalensky;Jiří Pergner;Michaela Liegertová;Èlia Benito-Gutiérrez;D. Arendt;Z. Kozmík
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文献类型：
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作者：
Pavel Vopalensky;Jiří Pergner;Michaela Liegertová;Èlia Benito-Gutiérrez;D. Arendt;Z. Kozmík
脊椎动物眼睛的起源仍然是个谜。文昌鱼是我们最原始的脊索动物亲戚，其“额眼”长期以来一直被认为是脊椎动物眼睛的候选祖先。然而，文昌鱼的额眼由简单的纤毛细胞组成，这与脊椎动物的视杆细胞和视锥细胞不同，后者显示出更复杂的、表面延伸的纤毛。到目前为止，证明额眼确实可能对光敏感的唯一证据是在暗色素细胞附近存在纤毛假定感觉细胞。我们着手从分子角度表征文昌鱼额眼的细胞类型，以测试它们与脊椎动物眼睛细胞类型的可能相关性。我们发现，额眼细胞特异性地共表达脊椎动物眼光感受器典型的转录因子和视蛋白的组合以及 G 蛋白的抑制性 Gi 型 α 亚基，这表明光转导级联反应不响应。此外，色素细胞在黑色素含量和调节特征上与视网膜色素上皮相匹配。最后，我们揭示了额眼的轴突投影，类似于脊椎动物前脑的基本感光运动回路。这些结果支持文昌鱼额眼和脊椎动物眼睛的同源性，并深入了解它们的进化起源。
The origin of vertebrate eyes is still enigmatic. The “frontal eye” of amphioxus, our most primitive chordate relative, has long been recognized as a candidate precursor to the vertebrate eyes. However, the amphioxus frontal eye is composed of simple ciliated cells, unlike vertebrate rods and cones, which display more elaborate, surface-extended cilia. So far, the only evidence that the frontal eye indeed might be sensitive to light has been the presence of a ciliated putative sensory cell in the close vicinity of dark pigment cells. We set out to characterize the cell types of the amphioxus frontal eye molecularly, to test their possible relatedness to the cell types of vertebrate eyes. We show that the cells of the frontal eye specifically coexpress a combination of transcription factors and opsins typical of the vertebrate eye photoreceptors and an inhibitory Gi-type alpha subunit of the G protein, indicating an off-responding phototransductory cascade. Furthermore, the pigmented cells match the retinal pigmented epithelium in melanin content and regulatory signature. Finally, we reveal axonal projections of the frontal eye that resemble the basic photosensory-motor circuit of the vertebrate forebrain. These results support homology of the amphioxus frontal eye and the vertebrate eyes and yield insights into their evolutionary origin.