The formation of the Bicoid morphogen gradient requires protein movement from anteriorly localized mRNA.
The formation of the Bicoid morphogen gradient requires protein movement from anteriorly localized mRNA.
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DOI：
10.1371/journal.pbio.1000596
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发表时间：
2011-03
期刊：
影响因子：
9.8
通讯作者：
Gregor T
中科院分区：
文献类型：
--
作者：
Little SC;Tkačik G;Kneeland TB;Wieschaus EF;Gregor T
新的定量数据表明，双聚体形态梯度是由动态局部源产生的，并且蛋白梯度形成需要沿前后轴的蛋白质运动。
双子形态梯度将细胞命运的模式引导沿合成果蝇胚胎的前轴轴，并用作形态学介导的图案的范式。梯度形成的最简单模型依赖于恒定的蛋白质合成和从前局部源的mRNA的扩散，并与均匀的蛋白质降解相结合。但是，当前这些模型无法说明所有已知的梯度特征。最近的工作提出，双子mRNA空间分布足以产生观察到的蛋白质梯度，从而最大程度地减少了蛋白质转运的作用。在这里，我们适应了一种新型的荧光原位杂交方法，以量化双粒mRNA颗粒的全局时空动力学。我们确定在胚胎的前20％之内，所有双双聚体mRNA中的> 90％持续存在。尽管动态mRNA易位从胚胎芯到皮层，但沿着体轴的双聚体mRNA分布几乎保持不变。为了评估mRNA分布对蛋白质梯度动力学的影响，我们在形成蛋白质梯度的过程中提供了详细的定量测量核双子水平。我们发现梯度建立在受精后45分钟开始，梯度需要约50分钟才能达到峰值水平。在梯度形成的数值模拟中，我们发现合并实际的双子mRNA分布与从前极点源的点源建模蛋白质产生相比，观察到的蛋白质动力学的预测更仔细地预测。我们得出的结论是，双子素mRNA的空间分布对蛋白质梯度的形成有助于但无法解释蛋白质梯度的形成，因此，梯度形成是必需的蛋白质运动或被动的。
双子蛋白梯度在确定果蝇胚胎的前体模式中起着至关重要的作用。该梯度是形态学介导的后代模式的经典例子，并作为数学建模的主要主题。梯度的准确建模需要详细说明潜在的双子mRNA分布。经典模型认为，mRNA蛋白梯度是通过蛋白质从局部位于发育卵前的mRNA扩散而产生的。相反，最近的建议表明mRNA梯度会产生蛋白质梯度而无需蛋白质运动。在这项研究中，我们引入了一种新型的果蝇胚胎mRNA定量方法，这使我们能够在整个胚胎中准确地可视化每个单独的mRNA粒子。我们证明，除几个mRNA颗粒以外的所有mRNA颗粒都局限于卵的前部20％，因此必须移动蛋白质才能建立梯度。我们进一步报告，在蛋白质合成时期，mRNA分布是高度动态的。在数值模拟中，我们表明，在整个发育周期中融合各个源mRNA分子的现实空间位置是必要的，以准确地对实验观察到的蛋白梯度动力学进行建模。
New quantitative data show that the Bicoid morphogen gradient is generated from a dynamic localized source and that protein gradient formation requires protein movement along the anterior-posterior axis. The Bicoid morphogen gradient directs the patterning of cell fates along the anterior-posterior axis of the syncytial Drosophila embryo and serves as a paradigm of morphogen-mediated patterning. The simplest models of gradient formation rely on constant protein synthesis and diffusion from anteriorly localized source mRNA, coupled with uniform protein degradation. However, currently such models cannot account for all known gradient characteristics. Recent work has proposed that bicoid mRNA spatial distribution is sufficient to produce the observed protein gradient, minimizing the role of protein transport. Here, we adapt a novel method of fluorescent in situ hybridization to quantify the global spatio-temporal dynamics of bicoid mRNA particles. We determine that >90% of all bicoid mRNA is continuously present within the anterior 20% of the embryo. bicoid mRNA distribution along the body axis remains nearly unchanged despite dynamic mRNA translocation from the embryo core to the cortex. To evaluate the impact of mRNA distribution on protein gradient dynamics, we provide detailed quantitative measurements of nuclear Bicoid levels during the formation of the protein gradient. We find that gradient establishment begins 45 minutes after fertilization and that the gradient requires about 50 minutes to reach peak levels. In numerical simulations of gradient formation, we find that incorporating the actual bicoid mRNA distribution yields a closer prediction of the observed protein dynamics compared to modeling protein production from a point source at the anterior pole. We conclude that the spatial distribution of bicoid mRNA contributes to, but cannot account for, protein gradient formation, and therefore that protein movement, either active or passive, is required for gradient formation. The Bicoid protein gradient plays a crucial role in determining the anterior body pattern of Drosophila embryos. This gradient is the classic example of morphogen-mediated patterning of a developing metazoan and serves as a major topic for mathematical modeling. Accurate modeling of the gradient requires a detailed account of the underlying bicoid mRNA distribution. The classic model holds that mRNA protein gradient arises via protein diffusion from mRNA localized at the anterior of the developing egg. In contrast, recent proposals suggest that an mRNA gradient generates the protein gradient without protein movement. In this study, we introduce a novel mRNA quantification method for Drosophila embryos, which allows us to visualize each individual mRNA particle accurately in whole embryos. We demonstrate that all but a few mRNA particles are confined to the anterior 20% of the egg, and consequently that the protein must move in order to establish a gradient. We further report that the mRNA distribution is highly dynamic during the time of protein synthesis. In numerical simulations, we show that incorporating realistic spatial locations of the individual source mRNA molecules throughout the developmental period is necessary to accurately model the experimentally observed protein gradient dynamics.
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影响因子：
11.4
作者：
Ferrandon, D;Koch, I;NussleinVolhard, C
通讯作者：
NussleinVolhard, C
影响因子：
64.5
作者：
Cha, BJ;Koppetsch, BS;Theurkauf, WE
通讯作者：
Theurkauf, WE
DOI：
10.1073/pnas.0509483102
发表时间：
2005-12-20
影响因子：
11.1
作者：
Gregor, T;Bialek, W;Wieschaus, EF
通讯作者：
Wieschaus, EF
DOI：
10.1073/pnas.0807655106
发表时间：
2009-02-10
影响因子：
11.1
作者：
Hecht, Inbal;Rappel, Wouter-Jan;Levine, Herbert
通讯作者：
Levine, Herbert
影响因子：
2
作者：
Alves, Filipa;Dilao, Rui
通讯作者：
Dilao, Rui