5 research outputs found
Sox2 regulatory sequences direct expression of a beta-geo transgene to telencephalic neural stem cells and precursors of the mouse embryo, revealing regionalization of gene expression in CNS stem cells
Sox2 is one of the earliest known transcription factors
expressed in the developing neural tube. Although it is
expressed throughout the early neuroepithelium, we show
that its later expression must depend on the activity of more
than one regionally restricted enhancer element. Thus, by
using transgenic assays and by homologous recombinationmediated
deletion, we identify a region upstream of Sox2
(-5.7 to -3.3 kb) which can not only drive expression of a
b-geo transgene to the developing dorsal telencephalon, but
which is required to do so in the context of the endogenous
gene. The critical enhancer can be further delimited to
an 800 bp fragment of DNA surrounding a nuclease
hypersensitive site within this region, as this is sufficient to
confer telencephalic expression to a 3.3 kb fragment
including the Sox2 promoter, which is otherwise inactive in
the CNS.
Expression of the 5.7 kb Sox2 b-geo transgene localizes to
the neural plate and later to the telencephalic ventricular
zone. We show, by in vitro clonogenic assays, that
transgene-expressing (and thus G418-resistant) ventricular
zone cells include cells displaying functional properties of
stem cells, i.e. self-renewal and multipotentiality. We
further show that the majority of telencephalic stem cells
express the transgene, and this expression is largely
maintained over two months in culture (more than 40 cell
divisions) in the absence of G418 selective pressure. In
contrast, stem cells grown in parallel from the spinal cord
never express the transgene, and die in G418. Expression
of endogenous telencephalic genes was similarly observed
in long-term cultures derived from the dorsal
telencephalon, but not in spinal cord-derived cultures.
Thus, neural stem cells of the midgestation embryo are
endowed with region-specific gene expression (at least with
respect to some networks of transcription factors, such
as that driving telencephalic expression of the Sox2
transgene), which can be inherited through multiple
divisions outside the embryonic environment
Temporal and epigenetic regulation of neurodevelopmental plasticity
The anticipated therapeutic uses of neural stem cells depend on their ability to retain a certain level of developmental plasticity. In particular, cells must respond to developmental manipulations designed to specify precise neural fates. Studies in vivo and in vitro have shown that the developmental potential of neural progenitor cells changes and becomes progressively restricted with time. For in vitro cultured neural progenitors, it is those derived from embryonic stem cells that exhibit the greatest developmental potential. It is clear that both extrinsic and intrinsic mechanisms determine the developmental potential of neural progenitors and that epigenetic, or chromatin structural, changes regulate and coordinate hierarchical changes in fate-determining gene expression. Here, we review the temporal changes in developmental plasticity of neural progenitor cells and discuss the epigenetic mechanisms that underpin these changes. We propose that understanding the processes of epigenetic programming within the neural lineage is likely to lead to the development of more rationale strategies for cell reprogramming that may be used to expand the developmental potential of otherwise restricted progenitor populations