Proper differentiation of photoreceptors and amacrine cells depends on a regulatory loop between NeuroD and Six6
Proper differentiation of photoreceptors and amacrine cells depends on a regulatory loop between NeuroD and Six6
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DOI：
10.1242/dev.045294
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发表时间：
2010-07-15
期刊：
影响因子：
4.6
通讯作者：
Bovolenta, Paola
中科院分区：
文献类型：
--
作者：
Conte, Ivan;Marco-Ferreres, Raquel;Bovolenta, Paola
及时产生不同的神经细胞类型和适当的数量是产生一个功能视网膜的基础。在脊椎动物中，转录因子Six6最初在多能性视网膜祖细胞中表达，然后局限于分化的视网膜神经节细胞和无突细胞。Six6在视网膜中的表达是如何被控制的，以及它的确切功能是什么，目前还不清楚。为了解决这个问题，我们使用生物信息学搜索和转基因方法在medaka鱼（Oryzias latipes）中表征负责Six6表达的高度保守的调控增强子。其中一个增强子驱动分化和成年视网膜中的基因表达。转录因子结合位点的搜索、荧光素酶、ChIP测定和功能获得研究表明，bHLH转录因子NeuroD直接结合该增强子中存在的“E-box”序列，并特异性调节Six6在视网膜中的表达。在medaka胚胎中，neurod诱导的Six6过表达促进了无组织的视网膜祖细胞增殖，最值得注意的是，光感受器分化受损，而其他视网膜细胞类型没有明显变化。相反，Six6的功能获得和功能丧失改变了NeuroD的表达水平，并改变了光感受器分化标志物视紫红质的表达。此外，Six6的敲低会干扰无毛细胞的产生。综上所述，Six6和NeuroD相互调控表达，它们的功能协调了腺分泌细胞的产生和光感受器末端分化。
Timely generation of distinct neural cell types in appropriate numbers is fundamental for the generation of a functional retina. In vertebrates, the transcription factor Six6 is initially expressed in multipotent retina progenitors and then becomes restricted to differentiated retinal ganglion and amacrine cells. How Six6 expression in the retina is controlled and what are its precise functions are still unclear. To address this issue, we used bioinformatic searches and transgenic approaches in medaka fish (Oryzias latipes) to characterise highly conserved regulatory enhancers responsible for Six6 expression. One of the enhancers drove gene expression in the differentiating and adult retina. A search for transcription factor binding sites, together with luciferase, ChIP assays and gain-of-function studies, indicated that NeuroD, a bHLH transcription factor, directly binds an 'E-box' sequence present in this enhancer and specifically regulates Six6 expression in the retina. NeuroD-induced Six6 overexpression in medaka embryos promoted unorganized retinal progenitor proliferation and, most notably, impaired photoreceptor differentiation, with no apparent changes in other retinal cell types. Conversely, Six6 gain-and loss-of-function changed NeuroD expression levels and altered the expression of the photoreceptor differentiation marker Rhodopsin. In addition, knockdown of Six6 interfered with amacrine cell generation. Together, these results indicate that Six6 and NeuroD control the expression of each other and their functions coordinate amacrine cell generation and photoreceptor terminal differentiation.