Distinct allelic patterns of nanog expression impart embryonic stem cell population heterogeneity.
Distinct allelic patterns of nanog expression impart embryonic stem cell population heterogeneity.
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DOI：
10.1371/journal.pcbi.1003140
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发表时间：
2013
影响因子：
4.3
通讯作者：
Tzanakakis ES
中科院分区：
文献类型：
--
作者：
Wu J;Tzanakakis ES
Nanog 是一种主要的多能性调节因子，在体内和体外的干细胞群中表现出分散分布。越来越多的证据表明 Nanog 异质性对干细胞命运决定的功能作用。最近在小鼠胚胎干细胞中报道了 Nanog 基因表达的等位基因控制。为了更好地理解这种调节模式如何影响干细胞群体中观察到的 NANOG 异质性，我们组装了一个多尺度随机群体平衡方程框架。除了等位基因控制之外，还考虑了基因表达噪声和细胞分裂时的随机分配。作为等位基因 Nanog 表达的结果，Nanog 的分布表现出三种不同的状态，但当与转录噪声结合时，分布图变成双峰。无论其等位基因表达模式如何，最初均匀的干细胞群在十个细胞周期内产生相同的 Nanog 异质性。在细胞打开至少一个 Nanog 基因拷贝后，细胞中关闭两个基因等位基因时 NANOG 含量的耗尽速度慢于细胞内 NANOG 的积累，这表明 Nanog 状态依赖性动力学。 Nanog 的等位基因转录还引发了有关使用在单个等位基因座中敲除报告基因的干细胞系的问题。事实上，根据半衰期的差异以及报告基因在一个或两个等位基因中的插入情况，报告基因和天然蛋白质谱中观察到显着差异。在 Nanog 表达受限的干细胞群中，等位基因调节有助于维持具有足够 Nanog 含量的自我更新细胞部分，以防止多能性的异常丧失。我们的研究结果强调了 Nanog 表达的等位基因控制作为干细胞群体异质性的主要决定因素的作用，并值得在干细胞规范和细胞重编程的背景下进行进一步研究。 Nanog 是影响干细胞决定保持多能性或分化的关键因素。群体中的每个胚胎干细胞 (ESC) 都会表现出波动的 Nanog 水平，从而导致异质性，从而影响细胞命运规范。 Nanog 的等位基因调控最近得到证实，但其对群体异质性的影响尚不清楚。我们开发了多尺度人口平衡方程（PBE）模型，并将我们的结果与相关实验研究进行了比较。在等位基因控制下，Nanog 的特征具有三个峰或不同的状态。如前所述，转录噪声导致分布变成双峰。当检查等位基因调控位点中携带报告基因转基因的干细胞时，我们观察到内源蛋白和报告蛋白的分布不匹配。这促使我们根据转基因在一个或两个等位基因中的插入以及蛋白质降解动态来研究报告系统的性能。最后，我们的模型被用来解决等位基因调控如何影响单个 Nanog 等位基因缺失的干细胞多能性的维持。这些细胞的一部分仍保持多能性，而单个等位基因的缺失并不仅仅简单地均匀地降低所有 ESC 的 NANOG，而是直接调节 NANOG 异质性。
Nanog is a principal pluripotency regulator exhibiting a disperse distribution within stem cell populations in vivo and in vitro. Increasing evidence points to a functional role of Nanog heterogeneity on stem cell fate decisions. Allelic control of Nanog gene expression was reported recently in mouse embryonic stem cells. To better understand how this mode of regulation influences the observed heterogeneity of NANOG in stem cell populations, we assembled a multiscale stochastic population balance equation framework. In addition to allelic control, gene expression noise and random partitioning at cell division were considered. As a result of allelic Nanog expression, the distribution of Nanog exhibited three distinct states but when combined with transcriptional noise the profile became bimodal. Regardless of their allelic expression pattern, initially uniform populations of stem cells gave rise to the same Nanog heterogeneity within ten cell cycles. Depletion of NANOG content in cells switching off both gene alleles was slower than the accumulation of intracellular NANOG after cells turned on at least one of their Nanog gene copies pointing to Nanog state-dependent dynamics. Allelic transcription of Nanog also raises issues regarding the use of stem cell lines with reporter genes knocked in a single allelic locus. Indeed, significant divergence was observed in the reporter and native protein profiles depending on the difference in their half-lives and insertion of the reporter gene in one or both alleles. In stem cell populations with restricted Nanog expression, allelic regulation facilitates the maintenance of fractions of self-renewing cells with sufficient Nanog content to prevent aberrant loss of pluripotency. Our findings underline the role of allelic control of Nanog expression as a prime determinant of stem cell population heterogeneity and warrant further investigation in the contexts of stem cell specification and cell reprogramming. Nanog is a key factor influencing the decision of a stem cell to remain pluripotent or differentiate. Each embryonic stem cell (ESC) in a population exhibits fluctuating Nanog levels resulting in heterogeneity which affects cell fate specification. The allelic regulation of Nanog was demonstrated recently but its implications on population heterogeneity are unclear. We developed a multiscale population balance equation (PBE) model and compared our results with pertinent experimental studies. Under allelic control the profile of Nanog features three peaks or distinct states. Transcriptional noise causes the distribution to become bimodal as suggested previously. When stem cells carrying a reporter transgene in an allelically regulated locus were examined, we observed non-matching distributions of the endogenous and reporter proteins. This led us to investigate the performance of reporter systems depending on insertion of the transgene in one or both alleles and the protein degradation dynamics. Lastly, our model was employed to address how allelic regulation affects the maintenance of pluripotency in stem cells with a single Nanog allele deletion. A fraction of these cells remains pluripotent while deletion of a single allele does not simply reduce NANOG uniformly for all ESCs but modulates NANOG heterogeneity directly.
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