Am J Stem Cells 2013;2(2):74-94

Review Article
On becoming neural: what the embryo can tell us about differentiating neural stem

Sally A Moody, Steven L Klein, Beverley A Karpinski, Thomas M Maynard, Anthony-Samuel LaMantia

Department of Anatomy and Regenerative Biology, Department of Pharmacology and Physiology, Institute for Neuroscience, The George
Washington University, School of Medicine and Health Sciences, 2300 I (eye) Street, N.W., Washington, D.C. 20037, USA

Received March 22, 2013; Accepted May 17, 2013; Epub June 30, 2013; Published July 15, 2013

Abstract: The earliest steps of embryonic neural development are orchestrated by sets of transcription factors that control at least three
processes: 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. (AJSC1303003).

Keywords: Neural plate stem cells, neural gene regulatory network, FoxD5, FoxD4L1.1, FoxD4, neural induction, neural fate stabilization,
neural ectodermal precursors, neural progenitors, embryoid bodies, retinoic acid induction

Address correspondence to: Dr. Sally A Moody, Department of Anatomy and Regenerative Biology and Institute for Neuroscience, The
George Washington University, School of Medicine and Health Sciences, 2300 I (eye) Street, N.W., Washington, D.C. 20037, USA. Phone:
1-202-994-2878; Fax: 1-202-994-8885; E-mail:
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