Moody Sally A, Klein Steven L, Karpinski Beverley A, Maynard Thomas M, Lamantia Anthony-Samuel
Department of Anatomy and Regenerative Biology, The George Washington University, School of Medicine and Health Sciences 2300 I (eye) Street, N.W., Washington, D.C. 20037, USA ; Institute for Neuroscience, The George Washington University, School of Medicine and Health Sciences 2300 I (eye) Street, N.W., Washington, D.C. 20037, USA.
Am J Stem Cells. 2013 Jun 30;2(2):74-94. Print 2013.
the maintenance of proliferative, pluripotent precursors that expand the neural ectoderm; their transition to neurally committed stem cells comprising the neural plate; and the onset of differentiation of neural progenitors. The transition from one step to the next requires the sequential activation of each gene set and then its down-regulation at the correct developmental times. Herein, we review how these gene sets interact in a transcriptional network to regulate these early steps in neural development. A key gene in this regulatory network is FoxD4L1, a member of the forkhead box (Fox) family of transcription factors. Knock-down experiments in Xenopus embryos show that FoxD4L1 is required for the expression of the other neural transcription factors, whereas increased FoxD4L1 levels have three different effects on these genes: up-regulation of neural ectoderm precursor genes; transient down-regulation of neural plate stem cell genes; and down-regulation of neural progenitor differentiation genes. These different effects indicate that FoxD4L1 maintains neural ectodermal precursors in an immature, proliferative state, and counteracts premature neural stem cell and neural progenitor differentiation. Because it both up-regulates and down-regulates genes, we characterized the regions of the FoxD4L1 protein that are specifically involved in these transcriptional functions. We identified a transcriptional activation domain in the N-terminus and at least two domains in the C-terminus that are required for transcriptional repression. These functional domains are highly conserved in the mouse and human homologues. Preliminary studies of the related FoxD4 gene in cultured mouse embryonic stem cells indicate that it has a similar role in promoting immature neural ectodermal precursors and delaying neural progenitor differentiation. These studies in Xenopus embryos and mouse embryonic stem cells indicate that FoxD4L1/FoxD4 has the important function of regulating the balance between the genes that expand neural ectodermal precursors and those that promote neural stem/progenitor differentiation. Thus, regulating the level of expression of FoxD4 may be important in stem cell protocols designed to create immature neural cells for therapeutic uses.
胚胎神经发育的最早步骤由一系列转录因子协调，这些转录因子至少控制三个过程：维持增殖性、多能性前体细胞以扩展神经外胚层；它们向构成神经板的神经定向干细胞的转变；以及神经祖细胞分化的开始。从一个步骤到下一个步骤的转变需要每个基因集的顺序激活，然后在正确的发育时间对其进行下调。在此，我们综述了这些基因集如何在转录网络中相互作用以调节神经发育的这些早期步骤。这个调控网络中的一个关键基因是FoxD4L1，它是叉头框（Fox）转录因子家族的成员。非洲爪蟾胚胎中的敲低实验表明，FoxD4L1是其他神经转录因子表达所必需的，而FoxD4L1水平的升高对这些基因有三种不同的影响：神经外胚层前体基因的上调；神经板干细胞基因的短暂下调；以及神经祖细胞分化基因的下调。这些不同的影响表明，FoxD4L1将神经外胚层前体细胞维持在未成熟的增殖状态，并抵消神经干细胞和神经祖细胞的过早分化。由于它既能上调基因也能下调基因，我们对FoxD4L1蛋白中专门参与这些转录功能的区域进行了表征。我们在N端鉴定出一个转录激活结构域，在C端鉴定出至少两个转录抑制所需的结构域。这些功能结构域在小鼠和人类同源物中高度保守。对培养的小鼠胚胎干细胞中相关FoxD4基因的初步研究表明，它在促进未成熟神经外胚层前体细胞和延迟神经祖细胞分化方面具有类似的作用。这些在非洲爪蟾胚胎和小鼠胚胎干细胞中的研究表明，FoxD4L1/FoxD4具有调节扩展神经外胚层前体的基因与促进神经干/祖细胞分化的基因之间平衡的重要功能。因此，调节FoxD4的表达水平在旨在生成用于治疗用途的未成熟神经细胞的干细胞方案中可能很重要。
