Rethinking the neural crest - a novel dynamic hypothesis of neural crest fate restriction

体内所有类型的细胞都来自干细胞或其他前体细胞。这些前体是多能的，可以灵活地发育成多种类型的工作细胞(例如神经元、血液或皮肤细胞)中的任何一种。发育生物学中的一个主要问题是了解这些灵活的前体是如何对要采用的细胞类型进行具体选择的。一个事实说明了问题的严重性：对于一个关键的样本--神经脊干细胞，即使在研究了40年后，这个过程如何仍然存在不确定性--完全多能的细胞是直接跳到特定的选择命运上，还是经历一系列步骤，选择越来越有限，直到最终选择一种单一的细胞类型？这两种模型--直接命运限制(DFR)和渐进命运限制(PFR)--都得到了不同研究的支持，但相互冲突。虽然PFR现在是教科书上关于神经脊发育的观点，但一篇研究小鼠神经脊的著名论文最近以DFR解释得出了坚定的结论。作为BBSRC正在进行的一项研究斑马鱼胚胎中神经脊干细胞的工作的结果，我们提出了一种革命性的新观点，我们相信这一观点调和了这些冲突。我们一直在观察神经脊的色素细胞类型的形成，作为神经脊发育的一般模型。具体地说，我们一直在研究黑色素细胞(黑色色素细胞，因其在人类皮肤和头发颜色中的作用而闻名，并导致黑色素瘤)，以及虹膜载体，这是一种闪亮的银色细胞类型，在大多数鱼类中都很突出。我们只看到了一些非常广泛的多能前体的证据，这导致我们提出了我们的新的周期性命运限制模型。我们认为神经脊前体是可变的，因为它们是高度动态的，不断变化的。这一观点与实地相互矛盾的数据和解释是一致的，也是一致的。人们越来越多地使用数学建模方法来探索干细胞生物学，这种方法经常给出关于干细胞如何发挥作用的关键见解。也许令人惊讶的是，几乎所有这些工作都集中在“二元选择”上，因此忽略了DFR类型过程的可能性。即使对于PFR，建模也没有探索二元选择如何相互关联来产生多种不同的派生。在这个项目中，我们将测试和探索我们的新的周期性命运限制模型，使用实验研究和数学建模来深入了解这一过程可能是如何工作的。一个关键的实验是使用一种互补的技术来观察数千个神经脊细胞中的基因活动，全面观察它们的细胞图谱，以研究神经脊中可识别的前驱状态的范围。然后，我们将使用一种灵敏的技术直接观察胚胎中的这种细胞类型。同时，我们将探索这三个模型的数学基础，开发描述PFR的现有模型，并将新的理论见解应用于干细胞生物学，以研究DFR和我们的新周期模型的合理性。我们将结合这两种方法，通过实验研究与模型相关的生物学特征，包括直接评估前体细胞的变化方向，以及定量研究神经嵴中关键的命运指定信号。这些研究将共同检验神经脊干细胞生物学的革命性观点。了解这些过程的意义远远超出了我们在这里研究的基础生物学。这在医学上尤其重要，因为干细胞在不同细胞类型之间进行选择的过程对于了解健康的身体以及它在衰老和疾病中是如何出错的至关重要。因此，它将阐明先天性疾病和癌症的潜在机制。

All cell types in the body derive from stem or other precursor cells. These precursors are multipotent, having the flexibility to develop into any one of many types of working cells (e.g. neurons, blood or skin cells). A major problem in developmental biology is to understand how these flexible precursors make a specific choice of cell-type to adopt. The scale of the problem is illustrated by the fact that for one key exemplar, neural crest stem cells, there is still uncertainty about how the process works even after four decades of research - do fully multipotent cells 'jump' straight to a specific chosen fate, or do they go through a series of steps in which their options become more and more limited, until eventually they choose a single cell-type? These two models - Direct Fate Restriction (DFR) and Progressive Fate Restriction (PFR) - have each received support from different studies, but are conflicting. Although PFR is now the textbook view of neural crest development, a prominent paper studying mouse neural crest recently concluded firmly with a DFR interpretation. As a result of work done on an ongoing BBSRC grant studying neural crest stem cells in zebrafish embryos, we are proposing a revolutionary new view, which we believe reconciles these conflicts. We have been looking at the formation of pigment cell-types from the neural crest, as a model of neural crest development in general. Specifically, we have been looking at melanocytes (black pigment cells, well-known for their roles in skin and hair colour in humans, and giving rise to melanoma), and iridophores, a shiny silver cell-type that is prominent in most fishes. We see evidence for only some very broadly multipotent precursors, leading us to propose our novel Cyclical Fate Restriction model. We think that neural crest precursors are variable because they are highly dynamic, constantly changing. This view is consistent with, and reconciles, the conflicting data and interpretations in the field. Increasingly, stem cell biology is being explored using a mathematical modelling approach which has often given key insights into how they function. Surprisingly, perhaps, almost all this work has focused on 'binary choices', and so has ignored the possibilities of a DFR-type process. Even for PFR, modelling has not explored how binary choices might be interlinked to generate multiple diverse derivatives.In this project, we will test and explore our new Cyclical Fate Restriction model, using experimental studies and mathematical modelling to gain insight into how the process might work. A key experiment is to use a complementary technique to look at gene activity in thousands of neural crest cells, looking comprehensively at their cell-profiles so as to study the range of identifiable precursor states in the neural crest. We will then use a sensitive technique to look at such cell-types directly in the embryo. In parallel we will explore the mathematical basis for the three models, developing current models to describe PFR, and applying novel theoretical insights to stem cell biology to investigate the plausibility of both DFR and our novel Cyclical model. We will integrate the two approaches, experimentally investigating biological features relevant to the models, including direct assessment of the direction of change of progenitor cells, and quantitative investigation of the key fate specification signals in the neural crest.Together, these studies will test a revolutionary view of neural crest stem cell biology. Understanding these processes has implications well beyond the basic biology we are studying here. In particular, it is important in a medical context, in that this process of stem cells choosing between different cell-types is of fundamental importance to understanding the healthy body and how it goes wrong in ageing and in disease. It thus will shed light on the mechanisms underlying congenital diseases and cancer.