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A
B
C
Mes
Otx2
Wnt1
Met
E8.0-8.5
E9.5
Otx2
Wnt1
T
Gbx2
Otx2
E7.5
Fgf8
r2-4
Gbx2
Gbx2
Fgf8
Anterior
Posterior
mes
met
mes met
Gbx2
Otx2
Gbx2
Otx2
Wnt1
Fgf8
Gbx2
Otx2
Wnt1
Fgf8
FIGURE 2.16 The model of how the midbrain-hindbrain signaling center arises. A. The initial distinction
between the anterior and posterior of the embryonic nervous system is reflected in expression of otx2 and
gbx2 . C. At the boundary between these two factors, the mes-met boundary forms, and wnt1, en1, and FGF8
are all expressed in this region and act in a regulatory network to maintain their expression and this bound-
ary. (Modified from Joyner et al., 2000)
butions to the mature brain of particular regions of
the neural tube. One particularly useful interspecific
transplantation paradigm that was developed by
Nicole LeDouarin is to transplant tissues between
chick embryos and quail embryos, as described in the
previous section. Since these species are similar
enough at early stages of development, the trans-
planted cells integrate with the host and continue
developing along with them (Figure 2.17). The chick
and quail cells can be later distinguished since the
quail cells contain a more prominent nucleolus, which
can be identified following histological sectioning and
processing of the chimeric tissue. More recently, anti-
bodies specific for quail cells have been generated, and
these are also useful for identifying the transplanted
cells. The combination of vital dyes, cell injections,
and chick-quail transplant studies have produced a
description or “fate map” of the ultimate fates of the
various cells of the embryo. Figure 2.18 shows the fate
maps for amphibian (Eagleson and Harris, 1990),
avian, and mammalian neural tubes, for the basic
forebrain regions that have been derived from these
fate-mapping studies. The basic pattern has been
elaborated upon to generate the wide diversity of
brains that are found in vertebrates.
Although fate-mapping studies provide informa-
tion about the fate of the different neural tube regions,
embryologists have also investigated whether the fate
of the cells is fixed or can be changed. The goal of these
experiments, in general, is to provide a timetable for
Chick host
Quail donor
FIGURE 2.17 The interspecific transplantation paradigm was
developed by Nicole LeDouarin using chick embryos and quail
embryos. Tissue is dissected from quail embryos and then placed
into specific regions of live chick embryos. In this case, the dorsal
ridge of the neural tube, the region that will give rise to neural crest,
is transplanted to a similar region in the chick. The chick and quail
are similar enough to allow the quail to contribute to the chick
embryo, and the quail cells can be specifically identified with an
antibody raised against quail cells (bottom). (Modified from Le
Douarin et al., 2004)
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