Cell两篇文章挑战模式形成传统理论
第二篇文章中，Gregor与其同事发现胚胎能够区分Bicoid表达中的非常小的差异。核中，10％的Bicoid浓度差异可以决定下游基因活化与否。而且在不同果蝇的相应区域中，Bicoid的表达几乎是相同的。
然而，有些研究人员认为，Bicoid的表达仍有可能含有许多可变成分。辛辛那提儿童医院Jun Ma（未参与研究）认为，Bicoid的表达在某种程度上仍然比较混乱。“我不能排除有多层正确的修改机制能够基本上确保系统工作完好。”如果控制Bicoid表达的机制如作者所发现的，这会导致另一个问题：“是什么使Bicoid梯度如此精确的？”
还有一个问题是，胚胎在决定各个部位需要活化的基因时，是怎样区分Bicoid浓度间如此之小的差异的。Hanes说，总之，这项发现“引发的问题和其回答的问题一样多。”
原始出处:
Cell, Vol 130, 153-164, 13 July 2007
Article
Probing the Limits to Positional Information
Thomas Gregor,1,2,3,4,
David W. Tank,1,2,3 Eric F. Wieschaus,2,4 and William Bialek1,3
1 Joseph Henry Laboratories of Physics, Princeton University, Princeton, NJ 08544, USA
2 Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
3 Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
4 Howard Hughes Medical Institute, Princeton University, Princeton, NJ 08544, USA
Corresponding author
Thomas Gregor
tg2@princeton.edu
The reproducibility and precision of biological patterning is limited by the accuracy with which concentration profiles of morphogen molecules can be established and read out by their targets. We consider four measures of precision for the Bicoid morphogen in the Drosophila embryo: the concentration differences that distinguish neighboring cells, the limits set by the random arrival of Bicoid molecules at their targets (which depends on absolute concentration), the noise in readout of Bicoid by the activation of Hunchback, and the reproducibility of Bicoid concentration at corresponding positions in multiple embryos. We show, through a combination of different experiments, that all of these quantities are ∼10%. This agreement among different measures of accuracy indicates that the embryo is not faced with noisy input signals and readout mechanisms; rather, the system exerts precise control over absolute concentrations and responds reliably to small concentration differences, approaching the limits set by basic physical principles.
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