Stochastic Regulation of her1/7 Gene Expression Is the Source of Noise in the Zebrafish Somite Clock Counteracted by Notch Signalling.
Stochastic Regulation of her1/7 Gene Expression Is the Source of Noise in the Zebrafish Somite Clock Counteracted by Notch Signalling.
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DOI：
10.1371/journal.pcbi.1004459
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发表时间：
2015-11
影响因子：
4.3
通讯作者：
Lewis J
中科院分区：
文献类型：
--
作者：
Jenkins RP;Hanisch A;Soza-Ried C;Sahai E;Lewis J
体节分割时钟是一个强大的振荡器，用于在早期脊椎动物胚胎发生过程中产生规则大小的片段。有人提出，相邻细胞的时钟通过细胞间Notch信号同步，以克服噪声基因表达的影响。当细胞之间的Notch依赖性通信失败时，单个细胞的时钟不稳定地运行，并且在大约5到8个分段时钟周期（在斑马鱼中为2-3小时）的时间段内失去同步。在这里，我们定量研究随机性对细胞同步的影响，使用数学建模，调查这种噪音的可能来源。我们发现，在转录，翻译和降解速率的关键Notch信号调节的变化并不能解释在体内动力学的去磷酸化。相反，该分析预测，时钟去激活，在Notch信号的情况下，是由于随机解离的Her 1/7阻遏蛋白从振荡her 1/7自动阻遏的靶基因。使用原位杂交来可视化HER 1活性转录位点，我们测量到细胞中两个HER 1等位基因激活时间之间平均延迟约三分钟。我们的模型表明，这样的延迟足以解释Notch途径突变胚胎中的时钟去同步化的体内速率，并且Notch介导的同步足以克服这种随机变化。这表明阻遏物/DNA解离的随机性是分段时钟中噪声的主要来源。复杂生物体的解剖学依赖于发育过程中基因表达空间模式的可靠形成。许多因素必须协调来调节基因表达，这些事件的随机性可能会破坏模式的形成。模式形成的一个充分研究的例子是体节的连续形成，脊椎动物身体的胚胎部分。在该系统中，通过基因表达振荡器沿着身体的移动来产生空间图案。有效的模式形成需要相邻的细胞彼此同步振荡。遗传实验已经确定Notch信号是同步所需的，从而提出了Notch信号可以抵消该系统中的噪音的建议。然而，噪音的来源从未得到证实。通过数学建模，我们探索了不同的噪声源。我们发现，这种噪声的可能来源是关键振荡基因her 1/7的随机性。实验测量使我们能够测量每个细胞中两个her 1基因拷贝激活时间的延迟。这种延迟使我们能够估计her 1/7基因调控的随机性。该延迟解释了在没有Notch信令的情况下相邻小区去同步的速率。
The somite segmentation clock is a robust oscillator used to generate regularly-sized segments during early vertebrate embryogenesis. It has been proposed that the clocks of neighbouring cells are synchronised via inter-cellular Notch signalling, in order to overcome the effects of noisy gene expression. When Notch-dependent communication between cells fails, the clocks of individual cells operate erratically and lose synchrony over a period of about 5 to 8 segmentation clock cycles (2–3 hours in the zebrafish). Here, we quantitatively investigate the effects of stochasticity on cell synchrony, using mathematical modelling, to investigate the likely source of such noise. We find that variations in the transcription, translation and degradation rate of key Notch signalling regulators do not explain the in vivo kinetics of desynchronisation. Rather, the analysis predicts that clock desynchronisation, in the absence of Notch signalling, is due to the stochastic dissociation of Her1/7 repressor proteins from the oscillating her1/7 autorepressed target genes. Using in situ hybridisation to visualise sites of active her1 transcription, we measure an average delay of approximately three minutes between the times of activation of the two her1 alleles in a cell. Our model shows that such a delay is sufficient to explain the in vivo rate of clock desynchronisation in Notch pathway mutant embryos and also that Notch-mediated synchronisation is sufficient to overcome this stochastic variation. This suggests that the stochastic nature of repressor/DNA dissociation is the major source of noise in the segmentation clock. The anatomy of complex organisms depends on the reliable formation of spatial patterns of gene expression during development. Many factors have to be coordinated to regulate gene expression and stochasticity in these events could undermine pattern formation. One well-studied example of pattern formation is the sequential formation of somites, embryonic segments of the vertebrate body. In this system, a spatial pattern is generated by the movement of a gene expression oscillator along the body. Effective pattern formation requires that neighbouring cells oscillate in synchrony with one another. Genetic experiments have determined that Notch signalling is required for synchrony, leading to the proposal that Notch signalling counteracts noise in this system. However, the source of noise has never been demonstrated. Via mathematical modelling, we explore different sources of noise. We show that the likely source of this noise is the randomness of switching on of key oscillator genes, her1/7. Experimental measurements enable us to measure the delay in the timing of activation of the two her1 gene copies in each cell. This delay allows us to estimate the stochasticity in her1/7 gene regulation. This delay explains the rate of neighbouring cell desynchronisation in the absence of Notch signalling.