1 Institut de Génétique Humaine, UPR 1142 CNRS, 141 rue de la
Cardonille, 34396 Montpellier, Cedex 5, France
2 Centre de Recherche en Biologie Macromoléculaire, CNRS FRE 2593, 1919
Route de Mende, 34293 Montpellier, Cedex 5, France
3 Department of Pathology, Massachusetts General Hospital, Harvard Medical
School, Fruit Street, Boston, MA 02114, USA
Author for correspondence (e-mail:
desanta{at}igh.cnrs.fr)
Accepted 8 May 2004
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SUMMARY |
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Key words: SOX, SOX9, BMP, Gremlin, Stomach, Pyloric sphincter, Differentiation, Chick
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Introduction |
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Several molecular factors involved during GI tract development have been
identified (for reviews, see Roberts,
2000; de Santa Barbara et al., 2002a). We and others have shown
that Hox genes play important and active roles in patterning the gut along AP
axis and controls normal gut epithelial differentiation
(Roberts et al., 1998
;
Zakany and Duboule, 1999
;
Aubin et al., 2002
;
de Santa Barbara and Roberts,
2002
). Morphogenic factors also play key roles during gut
development and differentiation. Endodermal Shh expression was
described to regulate morphogenesis and mesenchymal differentiation through
the induction of Bmp4 in the adjacent mesoderm
(Roberts et al., 1995
;
Sukegawa et al., 2000
).
Ramalho-Santos and colleagues have shown more generally that hedgehog genes
play important roles during GI organogenesis, enteric nervous system (ENS)
development, epithelial proliferation and differentiation
(Ramalho-Santos et al., 2000
).
Bmp4, which is expressed in the gut mesoderm, is involved in
controlling growth and differentiation of the GI musculature
(Roberts et al., 1998
;
Smith et al., 2000a
;
Nielsen et al., 2001
). The
importance of all these factors in gut patterning is highlighted by their
remarkable conservation across vertebrate species
(Smith et al., 2000b
).
SOX genes, which encode high-mobility group (HMG) domain-containing
transcription factors, have been identified as key players in numerous
developmental processes, including sex determination, neurogenesis, muscle
differentiation, chondrogenesis and endoderm specification
(Wegner, 1999). Recently,
Sox17 has been shown to be necessary for the gut endoderm development
(Kanai-Azuma et al., 2002
).
SOX9 was initially identified as the gene responsible for campomelic
dysplasia (CD) syndrome, an autosomic dominant disease characterized by
skeletal malformations associated with sex reversal
(Cameron and Sinclair, 1997
).
Studies on SOX9 mainly focused on its role in skeletal and gonadal
development. However, individuals with CDs often display abnormalities in
visceral organs and brain, suggesting a role for SOX9 in some aspects of the
GI and central nervous system (CNS) development. Dysmorphogenesis have been
described in CD affected individuals in their GI tract, tracheopulmonary
system, urinary tract and heart (Maroteaux
et al., 1971
; Houston et al.,
1983
). Reported GI tract anomalies include megacolon and
intestinal malrotation (Houston et al.,
1983
). Owing to the high mortality, only a few studies have
addressed GI diseases or malformations in individuals with CD
(Piper et al., 2002
).
In this study, we have investigated the expression and function of SOX9 in visceral pattern formation using the chick embryo as a model system. We found that SOX9 was expressed throughout the gut endoderm sparing the gizzard during both avian and human GI development. Mesodermal expression is mainly restricted to the pyloric sphincter mesoderm. We provide evidence that Sox9 expression in the pyloric sphincter structure is under control of the BMP signaling pathway. Ectopic expression of SOX9 through retroviral misexpression technique in the gizzard mesoderm induces the transdifferentiation of the adjacent gizzard epithelium into a pyloric sphincter-like epithelium, whereas SOX9 loss-of-function expression in the pyloric mesoderm affects the differentiation of the pyloric epithelium. Taken together, our results show that SOX9 patterns the stomach/duodenum boundary and is necessary and sufficient to induce the differentiation of the pyloric epithelium.
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Materials and methods |
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Immunohistochemistry and in situ hybridization on gastrointestinal system
Immunohistochemical staining was performed on cryostat sections as
previously described (de Santa Barbara and
Roberts, 2002) using standard techniques and the Vectastain ABC
detection system (Vector Laboratories, CA) following the manufacturer's
directions. Used anti-SOX9 (
SOX9) antibodies were raised against the
transactivation domain of human SOX9 protein and used for immunohistochemistry
analyses diluted 1:100 in TBST (de Santa
Barbara et al., 1998
; de Santa
Barbara et al., 2000
). A full characterization in chick both by
western-blot and immunohistochemistry is available in Figs S1 and S2 at
http://dev.biologists.org/supplemental.
Anti-avian retroviral GAG protein (
3C2) antibodies were used as
previously described (de Santa Barbara and
Roberts, 2002
). Anti-HNK1 (
HNK1) antibodies were purchased
from NeoMarkers and used diluted 1:400. These antibodies recognize neural
crest-derived cells.
Antisense RNA probes were previously described for chick Bmp4
(Nielsen et al., 2001), chick
Gremlin (Capdevila et al.,
1999
), chick Nkx2.5, chick Shh
(Smith et al., 2000a
), chick
Sox8 (Bell et al., 2000
), chick
Sox9 (Healy et al., 1999
),
chick Sox10 (Cheng et al.,
2000
), chick Wnt11 (Theodosiou
and Tabin, 2003
), chick Pdx1 and chick Sox2
(Grapin-Botton et al., 2001
).
DIG labeled riboprobes were made following manufacturer's instructions
(Roche). Whole-mount in situ hybridization experiments were performed using a
standard protocol (Roberts et al.,
1998
). Cryosections (10 µm) were collected onto Superfrost Plus
slides (Fisher Scientific), air dried for 4-18 hours and kept at -20°C
until used. Fixed and stained embryos were embedded in paraffin wax and
sectioned at 8 µm for histological analysis. Haematoxylin and Eosin
staining was performed using standard techniques. In situ hybridization and
immunohistochemistry on paraffin wax-embedded sections were performed as
previously described (de Santa Barbara and
Roberts, 2002
).
Constructs and viral infection in the chick gastrointestinal tract
The viral constructs that we used were previously described, including
vectors transducing Bmp4 (Roberts
et al., 1998), Noggin
(Smith and Tabin, 1999
),
Nkx2.5 (Smith et al.,
2000a
), Gremlin
(Capdevila et al., 1999
) and
GFP (de Santa Barbara and
Roberts, 2002
).
New constructs were produced and characterized in this study (see Figs S1
and S2 at
http://dev.biologists.org/supplemental).
The full-length and C-terminal deleted (Cter) human SOX9 cDNAs
were cloned into the shuttle vector Slax13 and then subcloned into RCAS(A)
vector. Full-length and
Cter SOX9 RCAS vectors were
transfected into chick embryonic fibroblasts, and virus harvested and titered
using standard techniques (Morgan and
Fekete, 1996
). To target the presumptive stomach mesoderm,
misexpression experiments were performed on stage 10 embryos according to the
published fate map (Matsushita, 1995). Approximately 1-5 µl of freshly
thawed virus, dyed with 1% fast green, were injected per embryo. Eggs were
then placed at 38°C until harvested.
Photography
Images were collected in whole-mount under Nikon SMZ1000 scope and in
section under Zeiss Axiophot microscope, both using Nikon DXM1200 camera.
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Results |
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The function of SOX9 was recently shown to be dependent and regulated by
its nuclear-cytoplasmic translocation in the developing gonad
(de Santa Barbara et al.,
2000; Gasca et al.,
2002
). Only nuclear staining of SOX9 protein was observed in the
developing GI tract (Fig.
1B1-F1), whereas we observed SOX9 cytoplasmic expression in the
developing chick gonad before sexual differentiation, suggesting that SOX9
regulation might be context dependent (data not shown).
At E9 (stage 35), Sox9 expression was strongly detected in GI
derivate organs (such as lung, pancreas and liver), in the hindgut and in the
midgut (Fig. 2A). At this
stage, SOX9 expression in the esophageal epithelium is high at the base of the
villi and lower in the apex (Fig.
2B1). Strong nuclear expression of SOX9 protein was detected in
the midgut and caeca epithelia (Fig.
2D1,E1), as well as in the hindgut and the cloaca epithelia
(Fig. 2F1,G1) and the Fabricius
bursa epithelium (data not shown). Mesodermal expression of SOX9 was observed
at the caecal tips (Fig. 2E1).
In chick, the stomach consists of two regions, the proventriculus (avian
glandular stomach) and the gizzard (avian muscular stomach), which are
distinct both morphologically and physiologically
(Romanoff, 1960). The
connection between the gizzard and the duodenum is demarcated by the pyloric
sphincter. This structure is a mesodermal sphincter that allows for
maintaining food in the stomach and controls the gastric content flow into the
duodenum. Sox9 expression was also detected in the distal stomach in
a ring form corresponding to the pyloric sphincter
(Fig. 2A). SOX9 protein is
detected in the mesoderm of the pyloric sphincter
(Fig. 2C1). No colocalization
between SOX9- and HNK1-positive cells was observed (compare
Fig. 2C1 with C2).
|
|
E subgroup Sox gene expression in the chick stomach
SOX proteins constitute a large family of transcription factors
characterized by the presence of a HMG domain. Sequence homology outside of
HMG domains allowed distinguishing eight different groups
(Schepers et al., 2002).
Sox9 belongs to the E subgroup and shares strong homology with
Sox8 and Sox10, the other members of this subgroup. In
addition, overlapping functions and expressions of these E subgroup genes have
been previously described (Montero et al.,
2002
; Schmidt et al.,
2003
).
In order to determine whether SOX9 expression in the pyloric sphincter mesoderm is a common feature of all E subgroup Sox members or whether this expression pattern is specific to SOX9, we performed in situ hybridization experiments with Sox8, Sox9 and Sox10 riboprobes on chick E7 stomach. Expression of all three genes was detected in the stomach with specific expression patterns (Fig. 4A-C). Sox8 expression was detected in the pancreas and weak expression was also observed in ENS cells (Fig. 4B). Sox10 expression was restricted to ENS cells (Fig. 4C) and Sox9 expression was exclusively observed in the pyloric sphincter mesoderm (Fig. 4A). Together, our results demonstrate that SOX9 is the only E subgroup SOX member expressed in the pyloric sphincter mesoderm in vertebrates.
|
Overlapping expression patterns in the stomach suggest a potential
connection between BMP signaling pathway and SOX9. We, thus, investigated
whether BMP pathway could regulate Sox9 expression. We used the avian
retroviral technique to specifically misexpress Bmp4, Nkx2.5 and the
BMP-antagonist Noggin in the stomach mesoderm
(Roberts et al., 1998;
Nielsen et al., 2001
) and
monitored Sox9 expression by in situ hybridization experiments
(Fig. 5). GFP
misexpression was used as a control. Infection of mesoderm in the analyzed
stomach was confirmed by immunohistochemistry using antibodies directed
against the avian retroviral GAG protein (
3C2) (data not shown). As
previously reported, Bmp4 misexpression in the stomach induced a
gross phenotype characterized by a small gizzard with thin musculature
(Roberts et al., 1998
),
whereas the morphology of the pyloric sphincter was normal
(Fig. 5B). However, the domain
of Sox9 expression was extended anteriorly from the pyloric sphincter
to the right part of the gizzard (double red arrows,
Fig. 5B). This suggested that
activation of BMP signaling pathway in the stomach mesoderm upregulates
Sox9 expression. Examination of cryostat sections also indicated that
not all infected mesodermal cells express SOX9 in response to Bmp4
misexpression, suggesting that only few competent cells are able to respond to
BMP4 activation (red arrowheads, Fig.
5F). In similar experiments, Smith and Tabin
(Smith and Tabin, 1999
)
reported an extension of the expression domain of Nkx2.5 in the
stomach in response to Bmp4 misexpression. As previously described
(Smith et al., 2000a
), we
observed that Nkx2.5 misexpression in the stomach region did not
affect the morphology of the stomach and whole-mount in situ hybridization
analyses revealed that Sox9 expression pattern was not affected in
Nkx2.5-misexpressing stomach (Fig.
5C). Misexpression of Noggin, a specific secreted
antagonist of the BMP signaling pathway, in the stomach induced the predicted
phenotype of muscular hypertrophy (compare Fig.
5D,E with
5B). E8
Noggin-misexpressing stomachs develop a range of phenotypes from
moderate to severe (Fig. 5D,E).
Moderate phenotype was associated with a mild stomach/duodenum boundary
perturbation associated with downregulation of Sox9 expression
(compare Fig. 5D with
5A). Severe phenotype was
marked by a gross pyloric defect and correlated with the inhibition of
Sox9 expression in the malformed pyloric structure (compare Fig.
5E with
5A).
|
SOX9 is necessary and sufficient to specify the pyloric sphincter epithelium
In order to investigate more directly the role of SOX9 in pyloric sphincter
development, we used the avian retroviral system to specifically misexpress
full-length SOX9. Anterior misexpression of SOX9 into the
gizzard mesoderm did not lead to morphological change, but histological
analyses demonstrated an effect of SOX9 on gizzard epithelium
(Fig. 6C). In addition to
morphological and mesodermal differences, the gizzard and the pyloric
sphincter have epithelial morphologic differences. The gizzard epithelial
cells have a keratin layer and long cilia allowing resistance to the abrasive
grinding (Fig. 6A). The pyloric
sphincter epithelial cells have bulbous cilia without the keratin layer seen
in the gizzard (Fig. 6B).
SOX9 misexpression in the mesoderm of the gizzard modified the
gizzard epithelium to a pyloric sphincter-like epithelium with bleb-like cilia
(compare Fig. 6C with
6A). This epithelial
transformation was not due to the expression of ectopic SOX9 in the
gizzard epithelium as 3C2 and
SOX9 detections demonstrated that
retroviral infection was restricted to the gizzard mesoderm
(Fig. 6C inset, see Figs S1 and
S2 at
http://dev.biologists.org/supplemental).
In order to characterize the epithelial transformation observed upon
SOX9 misexpression, we analyzed by in situ hybridization the
expression of different endodermal markers (such as Shh, Sox2, Gata4
and Pdx1). Shh is a general marker of the gut endoderm
(Roberts et al., 1995
),
Sox2 and Gata4 are expressed in the stomach endoderm
(Ishii et al., 1998
)
(P.d.S.B., unpublished). Pdx1 is a marker of the duodenum, pancreas
and pyloric epithelia, but Pdx1 expression is not present in the
stomach epithelium (Grapin-Botton et al.,
2001
) (Fig. 6E).
Abnormal PDX1 expression in stomach has been described associated with the
pathologic presence of pseudopyloric glands in humans
(Sakai et al., 2004
).
SOX9 misexpression in the gizzard did not modify the expression of
Shh, Sox2 and Gata4 markers (data not shown). However, in
SOX9-misexpressing gizzards, we observed an ectopic expression of
Pdx1 in the gizzard epithelium, indicating that the transformed
gizzard epithelium exhibited characteristics of pyloric epithelium (red
arrowheads, Fig. 6F).
|
Together, our data show that the transcription factor SOX9 is necessary and sufficient to specify the pyloric sphincter epithelium through mesenchymal-epithelial signals.
Gremlin mediated SOX9 mesenchymal-epithelial function in the pyloric sphincter
Our results show that SOX9, which is expressed in the mesoderm of the
pyloric sphincter, specifies the adjacent epithelium. As SOX9 is a
transcription factor, we hypothesized that it may regulate the expression of
diffusible ligands, such as Wnts, BMPs or their related inhibitors, which were
described to be essential to establish pyloric epithelium phenotype through
mesenchymal-epithelial interaction
(Theodosiou and Tabin, 2003;
Smith and Tabin, 1999
).
Wnt11 expression, which is restricted to the pyloric sphincter
mesoderm, was not affected in SOX9 and SOX9
Cter-misexpressing
stomach (data not shown). We observed that Gremlin, a modulator of
the BMP pathway, was expressed in the mesoderm of the pyloric sphincter
(Fig. 7A,C). Anterior
misexpression of Gremlin in the gizzard mesoderm induced no gross
morphological phenotype, but, as does SOX9, did induce an epithelial
phenotype characterized by the presence of pyloric bleb like cells in the
gizzard epithelium (compare Fig.
7B with Fig. 6A).
These data suggested that Gremlin might be a potential candidate for
a downstream gene regulated by SOX9 in the pyloric sphincter. To test this
hypothesis, SOX9 and SOX9
Cter were misexpressed in the stomach
and Gremlin expression was monitored by in situ hybridization
(Fig. 7D,E). We observed an
ectopic Gremlin expression in the mesoderm of the gizzard with
full-length SOX9 (red arrowheads,
Fig. 7D). This was not detected
in SOX9
Cter-misexpressing stomach
(Fig. 7E). Nevertheless, we
observed a decrease of mesodermal Gremlin expression in the pyloric
structure upon SOX9
Cter misexpression (black arrowheads,
Fig. 7E). Finally, we found
that Sox9 expression was not affected in
Gremlin-misexpressing gizzard (data not shown).
|
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Discussion |
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|
Relationship between SOX9 and BMP signaling pathway during the specification of the pyloric sphincter epithelium
Establishment and differentiation of the stomach/duodenum boundary involved
a highly molecular regulated process as Bmp4
(Smith and Tabin, 1999) and
Nkx2.5 (Smith et al.,
2000a
). Bmp4 activates Nkx2.5 and alter the
epithelial differentiation to a pyloric sphincter type
(Smith and Tabin, 1999
;
Smith et al., 2000a
). We show
herein that activation and inhibition of BMP signaling pathway by viral
misexpression modulated Sox9 expression in the stomach
(Fig. 5). Gizzard retroviral
misexpression of Nkx2.5 leads to epithelial phenotype similar to
SOX9 misexpression [compare Smith et al., 2000
(Smith et al., 2000a
) with
Fig. 6]. Interestingly,
misexpression of SOX9 and SOX9
Cter in the stomach had no
effect on Bmp4 or Nkx2.5 expression (data not shown),
suggesting that SOX9 does not regulate the expression of these two genes. We
propose the following model in which BMP signaling pathway regulates
Sox9 and Nkx2.5 expression in the pyloric sphincter
(Fig. 8). These two
transcription factors could act independently or interact to specify the
pyloric sphincter epithelium. In support of this, genetic interactions between
SOX and Nkx2 family genes were reported in Drosophila to promote
neuroblast formation (Zhao and Skeath,
2002
).
|
In summary, our work reveal new functions of the transcription factor SOX9
during the GI tract development. SOX9 patterns the pyloric sphincter and
specifies the pyloric sphincter epithelium at least by regulating the
expression of Gremlin, a diffusible factor that modulates BMP
pathway. As we previously commented, molecular controls of GI development
patterning events are remarkably conserved across species. We hypothesize that
the described molecular mechanisms that control pyloric sphincter development
are conserved in human and that alterations of these mechanisms may account
for malformations such as hypertrophic pyloric stenosis
(Ohshiro and Puri, 1998).
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ACKNOWLEDGMENTS |
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Footnotes |
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* These authors contributed equally to this work
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REFERENCES |
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![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Aubin, J., Dery, U., Lemieux, M., Chailler, P. and Jeannotte,
L. (2002). Stomach regional specification requires
Hoxa5-driven mesenchymal-epithelial signaling.
Development 129,4075
-4087.
Bell, K. M., Western, P. S. and Sinclair, A. H. (2000). SOX8 expression during chick embryogenesis. Mech. Dev. 94,257 -260.[CrossRef][Medline]
Bernard, P., Tang, P., Liu, S., Dewing, P., Harley, V. R. and
Vilain, E. (2003). Dimerization of SOX9 is required for
chondrogenesis, but not for sex determination. Hum. Mol.
Genet. 12,1755
-1765.
Cameron, F. J. and Sinclair, A. H. (1997). Mutations in SRY and SOX9: testis-determining genes. Hum. Mutat. 9,388 -395.[CrossRef][Medline]
Capdevila, J., Tsukui, T., Rodriquez Esteban, C., Zappavigna, V. and Izpisua Belmonte, J. C. (1999). Control of vertebrate limb outgrowth by the proximal factor Meis2 and distal antagonism of BMPs by Gremlin. Mol. Cell 4,839 -849.[Medline]
Cheng, Y., Cheung, M., Abu-Elmagd, M. M., Orme, A. and Scotting, P. J. (2000). Chick sox10, a transcription factor expressed in both early neural crest cells and central nervous system. Brain Res. Dev. Brain Res. 121,233 -241.[Medline]
Chimal-Monroy, J., Rodriguez-Leon, J., Montero, J. A., Ganan, Y., Macias, D., Merino, R. and Hurle, J. M. (2003). Analysis of the molecular cascade responsible for mesodermal limb chondrogenesis: Sox genes and BMP signaling. Dev. Biol. 257,292 -301.[CrossRef][Medline]
Clatworthy, J. P. and Subramanian, V. (2001). Stem cells and the regulation of proliferation, differentiation and patterning in the intestinal epithelium: emerging insights from gene expression patterns, transgenic and gene ablation studies. Mech. Dev. 101, 3-9.[CrossRef][Medline]
Cremazy, F., Berta, P. and Girard, F. (2000). Sox neuro, a new Drosophila Sox gene expressed in the developing central nervous system. Mech. Dev. 93,215 -219.[CrossRef][Medline]
de Santa Barbara, P. and Roberts, D. J. (2002).
Tail gut endoderm and gut/genitourinary/tail development: a new tissue
specific role for Hoxa13. Development
129,551
-561.
de Santa Barbara, P., Bonneaud, N., Boizet, B., Desclozeaux, M.,
Moniot, B., Sudbeck, P., Scherer, G., Poulat, F. and Berta, P.
(1998). Direct interaction of the SRY-related protein SOX9 and
the steroidogenic factor-1 regulates transcription of the human
anti-Müllerian hormone gene. Mol. Cell. Biol.
18,6653
-6665.
de Santa Barbara, P., Moniot, B., Poulat, F. and Berta, P. (2000). Expression and sub-cellular localization of SF-1, SOX9, WT1 and AMH proteins during early human testicular development. Dev. Dyn. 217,293 -298.[CrossRef][Medline]
de Santa Barbara, P., van den Brink, G. R. and Roberts, D. J. (2002). Molecular etiology of gut malformations and diseases. Am. J. Med. Genet. 115,221 -230.[CrossRef][Medline]
de Santa Barbara, P., van den Brink, G. R. and Roberts, D. J. (2003). Development and differentiation of the intestinal epithelium. Cell. Mol. Life Sci. 60,1322 -1332.[CrossRef][Medline]
Gasca, S., Canizares, J., de Santa Barbara, P., Mejean, C.,
Poulat, F., Berta, P. and Boizet-Bonhoure, B. (2002). A
nuclear export signal within the high mobility group domain regulates the
nucleocytoplasmic translocation of SOX9 during sexual determination.
Proc. Natl. Acad. Sci. USA
99,11199
-11204.
Grapin-Botton, A., Majithia, A. R. and Melton, D. A.
(2001). Key events of pancreas formation are triggered in gut
endoderm by ectopic expression of pancreatic regulatory genes.
Genes Dev. 15,444
-454.
Healy, C., Uwanogho, D. and Sharpe, P. T. (1999). Regulation and role of Sox9 in cartilage formation. Dev. Dyn. 215,69 -78.[CrossRef][Medline]
Hamburger, V. and Hamilton, H. L. (1951). A series of normal stages in the development of the chick embryo. J. Morph. 88,49 -92.
Houston, C. S., Opitz, J. M., Spranger, J. W., Macpherson, R. I., Reed, M. H., Gilbert, E. F., Herrmann, J. and Schinzel, A. (1983). The campomelic syndrome: review, report of 17 cases, and follow-up on the currently 17-year-old boy first reported by Maroteaux et al. in 1971. Am. J. Med. Genet. 15, 3-28.[Medline]
Hui Yong Loh, S. and Russell, S. A. (2000). Drosophila group E Sox gene is dynamically expressed in the embryonic alimentary canal. Mech. Dev. 93,185 -188.[CrossRef][Medline]
Ishii, Y., Rex, M., Scotting, P. J. and Yasugi, S. (1998). Region-specific expression of chicken Sox2 in the developing gut and lung epithelium: regulation by epithelial-mesenchymal interactions. Dev. Dyn. 213,464 -475.[CrossRef][Medline]
Kanai-Azuma, M., Kanai, Y., Gad, J. M., Tajima, Y., Taya, C., Kurohmaru, M., Sanai, Y., Yonekawa, H., Yazaki, K., Tam, P. P. et al. (2002). Depletion of definitive gut endoderm in Sox17-null mutant mice. Development 129,2367 -2379.[Medline]
Maroteaux, P., Spranger, J., Opitz, J. M., Kucera, J., Lowry, R. B., Schimke, R. N. and Kagan, S. M. (1971). Le syndrome campomélique. Presse Med. 79,1157 -1162.[Medline]
Matsuhita, S. (1995). Fate mapping study of the splanchnopleural mesoderm of the 1.5-day-old chick embryo. Roux's Arch. Dev. Biol. 204,392 -399.
Montero, J. A., Giron, B., Arrechedera, H., Cheng, Y. C., Scotting, P., Chimal-Monroy, J., Garcia-Porrero, J. A. and Hurle, J. M. (2002). Expression of Sox8, Sox9 and Sox10 in the developing valves and autonomic nerves of the embryonic heart. Mech. Dev. 118,199 -202.[CrossRef][Medline]
Morgan, B. A. and Fekete, D. M. (1996). Manipulating gene expression with replication-competent retroviruses. Methods Cell. Biol. 51,185 -218.[Medline]
Nielsen, C., Murtaugh, L. C., Chyung, J. C., Lassar, A. and Roberts, D. J. (2001). Gizzard formation and the role of Bapx1. Dev. Biol. 231,164 -174.[CrossRef][Medline]
O'Rahilly, R. (1983). The timing and sequence of events in the development of the human reproductive system during the embryonic period proper. Anat. Embryol. 166,247 -261.[Medline]
Ohshiro, K. and Puri, P. (1998). Pathogenesis of infantile hypertrophic pyloric stenosis: recent progress. Pediatr. Surg. Int. 13,243 -252.[CrossRef][Medline]
Piper, K., Ball, S. G., Keeling, J. W., Mansoor, S., Wilson, D. I. and Hanley, N. A. (2002). Novel SOX9 expression during human pancreas development correlates to abnormalities in Campomelic dysplasia. Mech. Dev. 116,223 -226.[CrossRef][Medline]
Ramalho-Santos, M., Melton, D. A. and McMahon, A. P.
(2000). Hedgehog signals regulate multiple aspects of
gastrointestinal development. Development
127,2763
-2772.
Roberts, D. J. (2000). Molecular mechanisms of development of the gastrointestinal tract. Dev. Dyn. 219,109 -120.[CrossRef][Medline]
Roberts, D. J., Johnson, R. L., Burke, A. C., Nelson, C. E.,
Morgan, B. A. and Tabin, C. (1995). Sonic hedgehog is an
endodermal signal inducing Bmp-4 and Hox genes during induction and
regionalization of the chick hindgut. Development
121,3163
-3174.
Roberts, D. J., Smith, D. M., Goff, D. J. and Tabin, C. J.
(1998). Epithelial-mesenchymal signaling during the
regionalization of the chick gut. Development
125,2791
-2801.
Romanoff, A. L. (1960). "The Avian Embryo" New York, NY: Macmillan Company.
Sakai, H., Eishi, Y., Li, X. L., Akiyama, Y., Miyake, S.,
Takizawa, T., Konishi, N., Tatematsu, M., Koike, M. and Yuasa, Y.
(2004). PDX1 homeobox protein expression in pseudopyloric glands
and gastric carcinomas. Gut
53,323
-330.
Schepers, G. E., Teasdale, R. D. and Koopman, P. (2002). Twenty pairs of sox: extent, homology, and nomenclature of the mouse and human sox transcription factor gene families. Dev. Cell 3,167 -170.[Medline]
Schmidt, K., Glaser, G., Wernig, A., Wegner, M. and Rosorius,
O. (2003). Sox8 is a specific marker for muscle satellite
cells and inhibits myogenesis. J. Biol. Chem.
278,29769
-29775.
Smith, D. M. and Tabin, C. J. (1999). BMP signalling specifies the pyloric sphincter. Nature 402,748 -749.[CrossRef][Medline]
Smith, D. M., Nielsen, C., Tabin, C. J. and Roberts, D. J.
(2000a). Roles of BMP signaling and Nkx2.5 in patterning at the
chick midgut-foregut boundary. Development
127,3671
-3681.
Smith, D. M., Grasty, R. C., Theodosiou, N. A., Tabin, C. J. and Nascone-Yoder, N. M. (2000b). Evolutionary relationships between the amphibian, avian, and mammalian stomachs. Evol. Dev. 2,348 -359.[CrossRef][Medline]
Spokony, R. E., Aoki, Y., Saint-Germain, N., Magner-Fink, E. and Saint-Jeannet, J.-P. (2002). The transcription factor Sox9 is required for cranial neural crest development. Devlopment 129,421 -432.
Sudbeck, P., Schmitz, M. L., Baeuerle, P. A. and Scherer, G. (1996). Sex reversal by loss of the C-terminal transactivation domain of human SOX9. Nat. Genet. 13,230 -232.[Medline]
Sukegawa, A., Narita, T., Kameda, T., Saitoh, K., Nohno, T.,
Iba, H., Yasugi, S. and Fukuda, K. (2000). The concentric
structure of the developing gut is regulated by Sonic hedgehog derived from
endodermal epithelium. Development
127,1971
-1980.
Theodosiou, N. A. and Tabin, C. J. (2003). Wnt signaling during development of the gastrointestinal tract. Dev. Biol. 259,258 -271.[CrossRef][Medline]
Wegner, M. (1999). From head to toes: the
multiple facets of Sox proteins. Nucleic Acids Res.
27,1409
-1420.
Zakany, J. and Duboule, D. (1999). Hox genes and the making of sphincters. Nature 401,761 -762.[CrossRef][Medline]
Zhao, G. and Skeath, J. B. (2002). The
Sox-domain containing gene Dichaete/fish-hook acts in concert with vnd and ind
to regulate cell fate in the Drosophila neuroectoderm.
Development 129,1165
-1174.