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Fig. 1. Sequential generation of different classes of neurons and glia in
different domains of the ventral spinal cord. (A) Progenitor
domains in the ventral part of the mouse embryonic spinal cord. The vertical
axis represents the dorsoventral axis of the spinal cord, the horizontal axis
represents developmental time. (B) A cross-section of a mouse embryonic
spinal cord (dorsal, top), indicating the position of the progenitor domains
shown in A. Progenitor domains shown in A and B are: p0-p2, which generate
sequentially V0-V2 interneurons, oligodendrocytes and astrocytes; pMN, which
generates sequentially motor neurons (MNs), oligodendrocytes and astrocytes;
p3, which generates V3 interneurons, oligodendrocytes and astrocytes. In the
ventral spinal cord, oligodendrocyte progenitors (orange) are generated from
the pMN and p3 domains and also from the p0 and p1 domains
(Fogarty et al., 2005).
Patterning proteins (see Box
2), including the homeodomain (HD) proteins Pax6 and Nkx2.2, and
the basic helix-loop-helix (bHLH) protein Olig2, which establish the
progenitor domains, are initially coexpressed with the inhibitory HLH proteins
Id and Hes in uncommitted progenitor cells (grey). The induction of the
proneural proteins Ngn2 and Mash1 in progenitors promotes neurogenesis (blue),
whereas the induction of Mash1, the maintenance of Olig2 and Nkx2.2 and the
downregulation of Pax6 promote oligodendrogenesis (orange), and the
downregulation of patterning proteins and the maintenance of inhibitory HLH
proteins promote astrogenesis (pink). pD, progenitor domain for dorsal
neurons. See text and Sugimori et al.
(Sugimori et al., 2007) for
further details.
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