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Many of the structures affected by FAS
stem from neural crest cells (NCC), a group of cells derived
from the dorsal neuroectoderm during embryogenesis (Gilbert,
1997). Cartwright and Smith (1995) observed increased
aberrant cell death of NCC after ethanol exposure in chicks.
Sulik et al. (1988) also observed increased cell
death after exposure to ethanol in mammalian models. The
cranial neural crest, which leads to the formation of the
entire facial skeleton, is an especially sensitive target of
ethanol-induced apoptosis (Ahlgren et al., 2002).
These research teams suggest that this increased NCC death
may be responsible for FAS phenotypes.
More recent research has explored the
molecular causes of FAS. Expression of msx2, a
homeobox gene, is an integral factor of the development of
craniofacial structure and the developing brain. Expression
of msx2 was found to decrease in mice exposed to
alcohol (Rifas et al., 1997). The misexpression of
this gene corresponds to the affected FAS phenotypic areas
seen in previous research (Rifas et al., 1997).
Blader and Strähle (1998) found phenotypic disturbances
to be the result of misexpression of several ventral brain
markers, including shh, axl, and
Cell death is observed in the
premigratory and migratory neural crest cells, similar to an
observation made after blocking Sonic hedgehog (Shh)
signaling (Ahlgren et al., 2002). Ahlgren and
colleagues demonstrated that ethanol exposure results in a
loss of Shh and transcripts in the Shh signaling pathway,
and that ethanol-induced cranial NCC apoptosis and
associated growth defects can be salvaged by application of
Teratogens can also have different
effects on the developing embryo depending on the magnitude
and time of dose. Trunk NCC are precursors for the
peripheral nervous system, ganglia, and glial cells. They
are determined relatively late in migration, and thus are
multipotent and can compensate for some cell death. Alcohol
does not seem to affect these cells and their future
structures to the same degree as the cranial NCC (Smith,
1997). It has been found in chick embryos that alcohol
causes apoptosis of craniofacial cells only if treatment was
administered before the emigration of NCC from the
neurectoderm, at approximately 18 to 36 hours of development
(Smith, 1997). Since the fate of these cells are determined
at emigration, compensation for lost cells cannot occur in
the same manner as the trunk NCC and deformities are
observed (Bronner-Fraser and Fraser, 1991; Smith, 1997).
Cell death induced by alcohol may not
occur until 46-48 hours of development (Smith, 1997). To
observe areas of apoptosis, Fallon and Saunders (1968) first
reported the method of using the vital dye Neutral Red, and
this method has been published in recent works to reveal the
extent of cell death in tissues (Garcia-Martinez et
al., 1993; Kim and Mirkes, 2003).
Based on this knowledge, our
experiment investigates the phenotypic responses of FAS at
different treatment doses and times in the chick model.
Apoptosis in response to ethanol treatment is visualized
using Neutral Red staining techniques.
Last Modified: 10 May 2004
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