1 Division of Developmental Biology, Department of Cell and Molecular Biology,
and Center for Bioenvironmental Research, Tulane University, New Orleans, LA
70118, USA
2 College of Bioengineering, Fujian Normal University, Fuzhou, Fujian 350007, PR
China
Author for correspondence (e-mail:
ychen{at}tulane.edu)
Accepted 28 July 2005
![]() |
SUMMARY |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: Mouse, Cleft palate, Shox2, Epithelial-mesenchymal interaction
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The homeobox genes encode a class of transcription factors that control
many developmental processes during embryonic development in organisms as
diverse as humans and flies. Mutations in homeobox genes have been described
in a number of human genetic diseases
(Boncinelli, 1997), such as
PAX3 in Waardenburg syndrome
(Baldwin et al., 1992
),
PAX6 in aniridia (Glaser et al.,
1992
), PITX2 in Rieger syndrome
(Semina et al., 1996
), and
MSX1 in familial tooth agenesis and cleft palate
(Vastardis et al., 1996
;
Van den Boogaard et al.,
2000
). The SHOX gene (short stature homeobox gene) was
initially identified to be associated with idiopathic growth retardation and
Turner syndrome and Leri-Weill dyschondrosteosis in humans
(Ellison et al., 1997
;
Rao et al., 1997
;
Belin et al., 1998
;
Shears et al., 1998
).
SHOX has a closely related human homolog SHOX2
(SHOT or OG12X) (Blaschke
et al., 1998
; Semina et al.,
1998
). They share 83% homology at the amino acid level and have an
identical homeodomain. The expression of SHOX2 has been detected in
the limb bud, branchial arches, nasal processes, heart, central nervous system
and genital tubercle of human embryos
(Clement-Jones et al., 2000
).
However, SHOX2 has not yet been linked to any known syndromes so far.
A zooblot analysis of SHOX and SHOX2 revealed an absence of
both genes in all the invertebrates studied but their presence in all
vertebrates studied suggests that these two genes have a central role in the
development of the internal skeleton and its related structures
(Clement-Jones et al., 2000
).
An SHOX ortholog does not exist in mice, but the true mouse
Shox2 ortholog has been identified
(Rovescalli et al., 1996
;
Clement-Jones et al., 2000
).
The mouse Shox2 shares 99% identity at the amino acid level with its human
counterpart (Blaschke et al.,
1998
; Semina et al.,
1998
). The expression pattern of Shox2 in developing
mouse embryo is very similar to that of human SHOX2
(Blaschke et al., 1998
;
Semina et al., 1998
;
Clement-Jones et al., 2000
).
In humans, SHOX and SHOX2 exhibit an overlapping while
sometimes complementary expression pattern in a number of developing organs or
tissues, including the first and second branchial arch and their derivatives,
and the developing limb, suggesting a functional redundancy between them
(Clement-Jones et al., 2000
).
The lack of an SHOX ortholog in mice implicates that mouse
Shox2 may play a broader function than human SHOX2 in
embryogenesis.
In this study, we identified a restricted expression pattern of Shox2 in the anterior palatal shelves of both mouse and human embryos. We demonstrate that the initially restricted expression of Shox2 in the mouse palatal mesenchyme is induced by signals derived from the anterior palatal epithelium, among which BMP activity is indispensable. We further generated Shox2 mutant mice by gene targeting. Defective palatal growth and altered gene expression are found to be confined to the anterior palate where Shox2 is expressed, leading to an incomplete cleft within the anterior region. Our results demonstrate a crucially intrinsic role for Shox2 in mammalian palatogenesis.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
RT-PCR
E13.5 mouse embryos were used to isolate mRNA using an RNAqueous-4PCR kit
(Ambion). The first-strand cDNA synthesis was carried out using a SuperScript
kit (Invitrogen). A set of primers (upstream,
5'-CTGCCCCATTGATGTGTTATT-3'; downstream,
5'-CCTCCTCCTCCAGCACCT-3') that amplified a 368 bp sequence of exon
1 and exon 2, and a pair of primers (upstream,
5'-ACCAGCAAGAACTCCAGCAT-3'; downstream,
5'-GCCACACTCCTTTGTCCAGT-3') that amplified a 371 bp sequence
covering exon 4 to exon 6 of Shox2 were used for RT-PCR detection of
partial transcripts in the Shox2 mutants. The primers (upstream,
5'-TTCCGCAAGTTCACCTACC-3'; downstream,
5'-CGGGCCGGCCATGCTTTACG-3') that amplify a 361 bp cDNA product of
S15 RNA were included as the positive control for RT-PCT.
Histology, in situ hybridization and scanning electron microscopy (SEM)
Mouse embryos were dissected in cold PBS and fixed in 4% paraformaldehyde
(PFA) in PBS at 4°C overnight. Surgically and medically terminated human
embryos were collected, staged and fixed in 4% PFA, under the ethical
permission of the Ethics Committee of Fujian Normal University. For
histological analysis, samples were embedded in paraffin, sectioned at 8 µm
and stained with Hematoxylin and Eosin. Samples used for section in situ
hybridization were paraffin embedded and sectioned at 10 µm. At least two
identical samples of mutant and wild type were used for in situ hybridization
for each probe. Samples used for whole-mount in situ hybridization were
bleached with 6% H2O2 after fixation, and dehydrated
through a graded methanol series. Whole-mount and section in situ
hybridization were performed as previously reported
(Zhang et al., 1999). SEM was
carried out as described before (Zhang et
al., 2002
).
Tissue recombination and bead implantation
The secondary palatal shelves from E11.5 to E13.5 embryos were
microdissected in PBS. To separate the palatal epithelium from the mesenchyme,
isolated palatal shelves were incubated for 20 minutes in solution containing
0.5% trypsin and 2.5% pancreatin on ice, and then were transferred to
-MEM medium plus 20% fetal bovine serum on ice for an additional 10
minutes. Tissues were microsurgically separated. Tissue recombination and bead
implantation were carried out according to procedures described previously
(Chen et al., 1996
;
Zhang et al., 2002
). Briefly,
isolated palatal mesenchyme or intact palatal tissue (containing both the
epithelium and mesenchyme) was placed on filter in the Trowell type organ
cultures. For tissue recombination, donor palatal epithelia were placed on the
top of mesenchymal tissues in organ culture. For bead implantations,
protein-soaked beads (Affi-Gel blue agarose bead, 100-200 mesh, 75-150 µm
diameter, from Bio-RAD, Hercules, CA) were implanted into the palatal tissues
on the filter. Samples were harvested for whole-mount in situ hybridization
analysis after 24 hours in culture in
-MEM media with 3500 mg/l
glucose, 0.55 mM glycine, 0.056 mM ascorbic acid and 14% knockout serum
replacement. The following proteins (with the concentration at which they were
used) were obtained from R&D System (Minneapolis, MN) and used for bead
implantation: activin (200 ng/µl), Bmp2 (200 ng/µl), Bmp4 (200
ng/µl), Bmp5 (200 ng/µl), Bmp7 (200 ng/µl), Fgf2 (500 ng/µl), Fgf4
(500 ng/µl), Fgf8 (200 ng/µl), Fgf10 (500 ng/µl), noggin (200
ng/µl) and Shh (1 µg/µl). Anti-Shh antibodies (5E1), obtained from
the Developmental Studies Hybridoma Bank, University of Iowa, Iowa City, IA,
were used at 400 ng/µl.
|
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Shox2 homozygous mutants exhibit impaired palatal development
To investigate the role of Shox2 in palatal development, we
inactivated Shox2 by deleting exon 3 which encodes the homeodomain of
the Shox2 protein (Fig. 2A).
The targeted locus in ES cells and germline transmission were confirmed by
Southern blot analysis (Fig.
2B). Heterozygous and homozygous mice were maintained on the
C57Bl/6 background and were genotyped by PCR
(Fig. 2C). To confirm an
absence of Shox2 expression in Shox2-deficient mice, RT-PCT
was performed with primers that amplify sequences spanning exon 1 to exon 2
and exon 4 to exon 6 of the Shox2 gene, respectively. No partial
Shox2 transcripts were detected in Shox2 mutant embryos
(Fig. 2D). Mice heterozygous
for the Shox2 mutation appeared normal and fertile. No Shox2
homozygous mutant mice were identified at birth. Examination of staged embryos
revealed that death of homozygous mutants occurred at mid-gestation stage. Of
187 homozygous mutant embryos recorded that present in a Mendelian ratio, 63%
of mutant embryos died between E11.5 and E12.5, while the rest survived up to
E17.5. Cardiac and vascular defects appeared to contribute to the embryonic
lethality in Shox2 homozygotes (R. Espinoza, L.Y. and Y.P.C.,
unpublished). Strikingly, the mutant embryos manifested an incomplete clefting
in the anterior region of the palate (Fig.
3). At E15.0, when the secondary palate closes in the wild type, a
clefting, from the anterior extremity of the secondary palate to the first
molar level, could be seen in the mutant
(Fig. 3). The AP length of the
cleft appeared shortened at E17.5, probably owing to partial fusion of the
palate at the posterior domain in the mutants
(Fig. 3). Furthermore, it
appears that the secondary palate failed to fuse with the primary palate and
the nasal septum.
|
|
|
To test whether the ectopic Fgf10 expression in the anterior palatal mesenchyme of Shox2 mutant accounts for the defective cell proliferation, we carried out in vitro bead implantation experiment using the anterior and posterior region of E13.5 wild-type palatal shelves. Beads soaked with BSA (1 mg/ml), Fgf10 (500 ng/µl) or Fgf2 (500 ng/µl) were implanted onto the tissue explants. Explants were cultured for 20 hours and were pulsed for BrdU for 45 minutes prior to fixation. A significant lower level of BrdU-labeled cells was observed in the anterior palatal tissues (16/20) implanted with Fgf10-soaked beads (Fig. 7B), when compared with controls implanted with BSA beads (Fig. 7A). Fgf10-soaked beads, however, did not alter cell proliferation in the posterior palatal tissue (11/11) (Fig. 7D,E), further demonstrating differential responses of palatal tissue along the AP axis to Fgf10 induction. By contrast, Fgf2, which binds to all four Fgf receptors, stimulate cell proliferation in both anterior (12/12) (Fig. 7C) and posterior palatal tissues (8/8) (Fig. 7F). Thus, ectopically applied Fgf10 appears to inhibit cell proliferation in the anterior palate. Different Fgfs apparently act differently on cell proliferation in the developing palate.
|
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Diffusible growth factors play a pivotal role in mediating tissue
interactions, often leading to activation of gene expression in the adjacent
tissue (Thesleff et al., 1995;
Chen and Maas, 1998
). A number
of growth factors are expressed in developing palate or are implicated in
normal palate development, such as Bmp2, Bmp4 and Shh, that
are all expressed in the anterior palatal epithelium
(Zhang et al., 2002
), making
them potential inducers of Shox2. However, none of the growth factors
that were tested in this study was able to induce Shox2 expression in
the posterior palatal mesenchyme. By contrast, blocking of Bmp activity in the
anterior palatal epithelium by the Bmp antagonist Noggin led to a
downregulation of Shox2 expression in the anterior palatal
mesenchyme. These results demonstrate a necessary but not sufficient role for
Bmp in the induction of Shox2 expression. Shox2 induction
apparently requires participation of multiple factors.
Shox2 encodes an intrinsic regulator of the anterior palatal growth
Altered levels of cell proliferation and/or apoptosis in developing palate
often cause abnormal palatal growth, leading to cleft palate formation
(Zhang et al., 2002;
Ito et al., 2003
;
Lan et al., 2004
;
Rice et al., 2004
;
Alappat et al., 2005
). The
anterior region of the Shox2-/- palatal shelves appears
shorter and smaller, indicating an impaired palatal growth. The mutant
anterior palatal shelves are obviously too small to make contact after
elevation. This retarded growth in the anterior palate may also contribute to
the lack of fusion of the secondary palate with the primary palate and the
nasal septum. TUNEL analyses of the palatal shelves of
Shox2-/- embryos at E12.5 reveal an unaltered level of
cell apoptosis. However, a high level of apoptosis in the anterior palatal
epithelium at E13.5 was detected when Shox2 expression expands from
the palatal mesenchyme to the epithelium, suggesting a likely cell-autonomous
regulation of Shox2 on apoptosis. Deficient cell proliferation in the
anterior palatal mesenchyme was also identified. Thus, both altered apoptosis
and cell proliferation, confined to the region where Shox2 is
expressed, contribute to the retarded palatal growth in the Shox2
mutants. Gene expression analyses demonstrate that an unaltered expression of
a number of genes known to be crucial for normal palatogenesis, including
Msx1 and its downstream gene Bmp4, Pax9, Lhx8, Osr2, Jag2
and Tgfb3, in the Shox2-/- palatal shelves,
suggesting that these genes do not reside downstream of Shox2 in
palatogenesis. However, Fgf10 and its receptor Fgfr2 were
found to be ectopically expressed in the anterior palatal mesenchyme of the
mutants. It has been demonstrated that Fgf10/Fgfr2 signaling is required for
normal cell proliferation and survival in developing palate, and application
of exogenous Fgf10 can stimulate cell proliferation in the palatal epithelium
(Rice et al., 2004
). In
contrast to these observations, Fgf10 and Fgfr2c were
ectopically activated in the anterior palate of Shox2 mutants, where
defective cell proliferation and apoptosis were also found. In vitro
application of Fgf10 protein to the anterior palate could actually inhibit
cell proliferation. The opposite results observed in the current study and the
studies by Rice et al. (Rice et al.,
2004
) could be attributed to the different concentrations of Fgf10
protein that was used, or different regions along the AP axis of the palatal
shelves to which the protein was applied. It is true that a molecule may have
opposite functions at different concentrations or in different developing
organs. This can be exemplified by the fact that Bmp4 stimulates cell
proliferation in palatal mesenchyme and mandibular mesenchyme but exerts an
inhibitory effect on cell proliferation in developing lung
(Bellusci et al., 1996
;
Barlow and Francis-West, 1997
;
Zhang et al., 2002
).
Furthermore, Bmp4 was found to activate at a lower concentration but to
repress at a higher concentration the expression of Shh in the
developing tooth germ (Zhang et al.,
2000
). Several signaling pathways operate and form a signaling
network in the regulation of palatogenesis. Ectopic expression Fgf10
and Fgfr2c in the palatal mesenchyme of Shox2 mutants may
disrupt a precisely tuned balance in the signaling network that regulate cell
proliferation and survival in the anterior palate, leading to abnormal cell
division and apoptosis. As Fgf10 does not signal through Fgfr2c, the
ectopically expressed Fgfr2c might mediate signaling from other Fgfs that are
expressed in the developing palate. In normal palatogenesis, Shox2
appears to repress, although not necessarily directly, Fgf10 and
Fgfr2c expression in the anterior palatal mesenchyme.
Shox2-/- mice exhibit an unusual type of cleft secondary palate
Genes that are harbored within the human genomic region 3q22-26 were
thought to be responsible for blepharophimosis, Cornelia de Lange syndromes
and 3q duplication syndrome (Ireland et
al., 1991; Aqua et al.,
1995
; Fryns, 1995
;
Small et al., 1995
;
Allanson et al., 1997
;
Semina et al., 1998
). The
human SHOX2 gene is located at this precise site of the human genome,
and its mouse orthologue is mapped within the region syntenic to human 3q25-26
(Blaschke et al., 1998
;
Semina et al., 1998
). Because
of its chromosomal localization and the consistency of its expression pattern
in developing human and mouse embryos with the congenital defects of these
syndromes (Blaschke et al.,
1998
; Semina et al.,
1998
; Clement-Jones etal.,
2000
), SHOX2 was initially thought to be a potential
candidate gene for these syndromes. However, recent studies have linked NIPBL
to Cornelia de Lange syndrome and FOXL2 to blepharophimosis
(Crisponi et al., 2001
;
Gillis et al., 2004
;
Krantz et al., 2004
;
Tonkin et al., 2004
). Thus
far, SHOX2 has not yet been linked to any known syndrome in humans.
The lack of an SHOX ortholog in mice implies that mouse
Shox2 may play a broader function than human SHOX2 in
embryogenesis. Indeed, Shox2-/- mice die prenatally,
probably owing to cardiac failure, exhibiting a cleft palate phenotype (this
study) and other defects including shortened limbs as is characteristic of the
short stature syndromes (L.Y. and Y.P.C., unpublished).
Consistent with the confined Shox2 expression in the anterior
palatal shelves, Shox2-deficient mice show an incomplete anterior
clefting. Thus, the cleft is limited within the future hard palate, while the
future soft palate is unaffected. The unique anterior clefting phenotype in
Shox2-/- mice is clearly different from those seen in mice
carrying a genetically engineered or naturally occurring mutant gene reported
previously. It is generally considered that the clefts of the hard palate
invariably include soft-palate clefts
(Sperber, 2001). In humans
cleft hard palate with intact soft-palate is extremely unusual
(Schupbach, 1983
). This type
of cleft was even not classified in the Veau classification system, the
earliest widely accepted system that divided cleft anomalies of individuals
into four subgroups (Shprintzen,
2002
).
Human and rodents share great similarity in palate closure that begins at
the earliest point of contact and proceeds in the anterior and posterior
directions (Schupbach, 1983).
As the initial closure point is located within the anterior third of the
shelf, it is generally accepted that palatal closure occurs in an
anterior-to-posterior sequence until fusion is complete
(Schupbach, 1983
;
Kaufman and Bard, 1999
;
Sperber, 2001
;
Zhang et al., 2002
).
Clinically, the mildest form of cleft palate is bifid uvula or clefting of
posterior soft palate. Increasingly, severe clefts always have posterior
involvement and the clefting advances anteriorly in an opposite direction to
that of normal palatal fusion (Sperber,
2001
). Cleft hard palate with an intact soft-palate was seen in
humans but was thought to be caused by a postfusion rupture mechanism
(Fara, 1971
;
Mitts et al., 1981
;
Schupbach, 1983
). The
restricted SHOX2 expression in the human palate makes it a potential
candidate gene for this rare type of cleft. In a genetic study using
Msx1 mutant mice, Msx1 was found to be expressed in the very
anterior region of the secondary palatal shelves and controls cell
proliferation in the anterior palatal mesenchyme via regulating Bmp4
expression (Zhang et al.,
2002
). The Msx1 mutant palatal shelves elevate to the
dorsum of the tongue, but the anterior region of the palatal shelves appears
too small to make contact at the midline, leading to complete cleft of
secondary palate. Similar complete clefts resulted from a defect in the
anterior palate growth were also observed in Fgf10 mutants
(Rice et al., 2004
;
Alappat et al., 2005
). These
studies support the anterior-to-posterior closure model and suggest a
zipper-like mechanism for palatal closure
(Zhang et al., 2002
). However,
in the present study, we showed that mice lacking Shox2 have an
incomplete clefting within the anterior palate, while the posterior palate,
including the soft palate, closes and fuses normally. These results
demonstrate that the posterior palate can fuse independently of anterior
palate fusion, and call for a revision of the prevailing model on the palatal
closure sequence. However, we certainly cannot rule out the possibility that
in this particular Shox2 mutant model increased Fgf10
expression in the anterior palatal mesenchyme could signal to the posterior
palate and lead to posterior fusion. Nevertheless,
Shox2-/- mice represent a unique model for studying
pathogenesis of cleft hard palate.
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
Footnotes |
---|
Present address: Shanghai Research Center for Biomodel Organism, 88 Cailun
Road, Pudong, Shanghai, China 201203
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Alappat, S. R., Zhang, Z., Suzuki, K., Zhang, X., Liu, H., Jiang, R., Yamada, G. and Chen, Y. P. (2005). The cellular and molecular etiology of the cleft secondary palate in Fgf10 mutant mice. Dev. Biol. 277,102 -113.[CrossRef][Medline]
Allanson, J. E., Hennekam, R. C. and Ireland, M. (1997). De Lange syndrome: subjective and objective comparison of the classical and mild phenotypes. J. Med. Genet. 34,645 -650.[Abstract]
Aqua, M. S., Rizzu, P., Lindsay, E. A., Shaffer, L. G., Zackai, E. H., Overhauser, J. and Baldini, A. (1995). Duplication 3q syndrome: molecular delineation of the critical region. Am. J. Med. Genet. 55,33 -37.[CrossRef][Medline]
Baldwin, C. T., Hoth, C. F., Amos, J. A., da-Silva, E. O. and Milunsky, A. (1992). An exonic mutation in the HuP2 paired domain gene causes Waardenburg's syndrome. Nature 355,637 -638.[CrossRef][Medline]
Barlow, A. J. and Francis-West, P. H. (1997).
Ectopic application of BMP-2 and BMP-4 can change patterning of developing
chick facial primordia. Development
124,391
-398.
Belin, V., Cusin, V., Viot, G., Girlich, D., Toutain, A., Moncla, A., Vekemans, M., Le Merrer, M., Munnich, A. and Cormier-Daire, V. (1998). SHOX mutations in dyschondrosteosis (Lòei-Weill syndrome). Nat. Genet. 19, 67-69.[Medline]
Bellusci, S., Henderson, R., Winnier, G., Oikawa, T. and Hogan,
B. L. M. (1996). Evidence from normal expression and targeted
misexpression that Bone Morphogenetic Protein-4 (Bmp-4)
plays a role in mouse embryonic lung morphogenesis.
Development 122,1693
-1702.
Blaschke, R. J., Monaghan, A. P., Schiller, S., Schechinger, B.,
Rao, E., Padilla-Nash, H., Ried, T. and Rappold, G. A.
(1998). SHOT, a SHOX-related homeobox gene, is implicated in
craniofacial, brain, heart, and limb development. Proc. Natl. Acad.
Sci. USA 95,2406
-2411.
Boncinelli, E. (1997). Homeobox genes and disease. Curr. Opin. Genet. Dev. 7, 331-337.[CrossRef][Medline]
Chai, Y., Jiang, X., Ito, Y., Bringas, P., Jr, Han, J., Rowitch,
D., Soriana, P., McMahon, A. and Sucov, H. (2000.). Fate of
the mammalian cranial neural crest during tooth and mandibular morphogenesis.
Development 127,1671
-1679.
Chen, Y. P. and Maas, R. (1998). Signaling loops in the reciprocal epithelial-mesenchymal interactions of mammalian tooth development. In Molecular basis of epithelial appendage morphogenesis (ed. C.-M, Chuong), pp.265 -282. Austin, TX: RG Landes.
Chen, Y. P., Bei, M., Woo, I., Satokata, I. and Maas, R.
(1996). Msx1 controls inductive signaling during
mammalian tooth morphogenesis. Development
122,3035
-3044.
Clement-Jones, M., Schiller, S., Rao, E., Blaschke, R. J.,
Zuniga, A., Zeller, R., Robson, S. C., Binder, G., Glass, I., Strachan, T. et
al. (2000). The short stature homeobox gene SHOX is
involved in skeletal abnormalities in Turner syndrome. Hum. Mol.
Genet. 9,695
-702.
Crisponi, L., Deiana, M., Loi, A., Chiappe, F., Uda, M., Amati, P., Bisceglia, L., Zelante, L., Nagaraja, R., Procu, S. et al. (2001). The putative forkhead transcription factor FOXL2 is mutated in blepharonphimosis/ptosis/epicanthus inversus syndrome. Nat. Genet. 27,132 -134.[CrossRef][Medline]
Cui, X.-M., Shiomi, N., Chen, J., Saito, T., Yamamoto, T., Ito, Y., Bringas, P., Chai, Y. and Shuler, C. F. (2005). Overexpression of Smad2 in Tgf-ß3-null mutant mice rescues cleft palate. Dev. Biol. 278,193 -202.[CrossRef][Medline]
De Moerlooze, L., Spencer-Dene, B., Revest, J., Hajihosseni, M.,
Rosewell, I. and Dickson, C. (2000). An important role for
the IIIb isoform of fibroblast growth factor receptor 2 (FGFR2) in
mesenchymal-epithelial signaling during mouse organogenesis.
Development 127,483
-492.
Ellison, J. W., Wardak, Z., Young, M. F., Robey, P. G.,
Laig-Webster, M. and Chiong, W. (1997). PHOG, a candidate
gene for involvement in the short stature of Turner syndrome. Hum.
Mol. Genet. 6,1341
-1347.
Fara, M. (1971). Congeital defects in the hard palate. Plast. Reconstr. Surg. 48, 44-47.
Ferguson, M. W. J. (1988). Palate development. Development Suppl. 103,41 -60.
Ferguson, M. W. J. and Honig, L. S. (1984). Epithelial-mesenchymal interactions during vertebrate palatogenesis. Curr. Top. Dev. Biol. 19,138 -164.
Fryns, J. P. (1995). The occurrence of the blepharophimosis, ptosis, epicanthus inversus syndrome and Langer type of mesomelic dwarfism in the same patient. Evidence of the location of Langer type of mesomelic dwarfism at 3q22.3-q23? Clin. Genet. 48,111 -112.[Medline]
Gillis, L. A., McCallum, J., Kaur, M., DeScipio, C., Yaeger, D., Mariani, A., Kline, A. D., Li, H. H., Devoto, M. and Jackson, L. G. (2004). NIPBL mutational analysis in 120 individuals with Cornelia de Lange sundrome and evaluation of genotype-phenotype correlations. Am. J. Hum. Genet. 75,610 -623.[CrossRef][Medline]
Glaser, T., Walton, D. S. and Maas, R. L. (1992). Genomic structure, evolutionary conservation and aniridia mutations in the human PAX6 gene. Nat. Genet. 2, 232-239.[CrossRef][Medline]
Greene, R. M. and Pratt, R. M. (1976). Developmental aspects of secondary palate development. J. Embryol. Exp. Morph. 36,225 -245.[Medline]
Herr, A., Meunier, D., Müller, I., Rump, A., Fundele, R., Ropers, H. H. and Nuber, U. A. (2003). Expression of mouse Tbx22 support its role in palatogenesis and glossogenesis. Dev. Dyn. 226,579 -586.[CrossRef][Medline]
Ireland, M., English, C., Cross, I., Houlsby, W. T. and Burn, J. (1991). A de novo translocation t(3;17)(q26.3;q23.1) in a child with Cornelia de Lange syndrome. J. Med. Genet. 28,639 -640.[Abstract]
Ito, Y., Yeo, J. Y., Chytil, A., Han, J., Bringas, P., Jr,
Nakajima, A., Shuler, C., Moses, H. L. and Chai, Y. (2003).
Conditional inactivation of Tgfbr2 in cranial neural crest causes
cleft palate and calvaria defects. Development
130,5269
-5280.
Johnston, M. C. and Bronsky, P. T. (1995).
Prenatal craniofacial development: new insights on normal and abnormal
mechanisms. Crit. Rev. Oral. Biol. Med.
6, 368-422.
Kaufman, M. H. and Bard, J. B. L. (1999). The Anatomical Basis of Mouse Development. Academic Press, San Diego, CA.
Krantz, I. D., McCallum, J., DeScipio, C., Kaur, M., Gillis, L. A., Yaeger, D. Jukofsky, L., Wasserman, N., Bottani, A., Morris, C. A. et al. (2004). Cornelia de Lange syndrome is caused by mutations in NIPBL, the human homolog of Drosophila melanogaster Nipped-B. Nat. Genet. 36,631 -635.[CrossRef][Medline]
Lan, Y., Ovitt, C. E., Cho, E.-S., Maltby, K. M., Wang, Q. and
Jiang, R. (2004). Odd-skipped related 2 (Osr2)
encodes a key intrinsic regulator of secondary palate growth and
morphogenesis. Development
131,3207
-3216.
Lee, S., Crisera, C. A., Erfani, S., Maldonado, T. S., Lee, J. J., Alkasab, S. L. and Longaker, M. T. (2001). Immunolocalization of fibroblast growth factor receptors 1 and 2 in mouse palate. Plast. Reconstr. Surg. 107,1776 -1784.[CrossRef][Medline]
Mitts, T. F., Garrett, W. S. and Hurwitz, D. J. (1981). Cleft of the hard palate with soft palate integrity. Cleft Palate J. 18,204 -206.[Medline]
Peters, H., Neubuser, A., Kratochwil, K. and Balling, R.
(1998). Pax9-deficient mice lack pharyngeal pouch
derivatives and teeth and exhibit craniofacial and limb abnormalities.
Genes Dev. 12,2735
-2747.
Rao, E., Weiss, B., Fukami, M., Rump, A., Niesler, B., Mertz, A., Muroya, K., Binder, G., Kirsch, S., Winkelmann, M. et al. (1997). Pseudoautosomal deletions encompassing a novel homeobox gene cause growth failure in idiopathic short stature and Turner syndrome. Nat. Genet. 16,54 -63.[CrossRef][Medline]
Rice, R., Spencer-Dene, B., Connor, E. C., Gritli-Linde, A.,
McMahon, A. P., Dickson, C., Thesleff, I. and Rice, D. P. C.
(2004). Disruption of Fgf10/Fgfr2b-coordinated
epithelial-mesenchymal interactions causes cleft palate. J. Clin.
Invest. 113,1692
-1700.
Rovescalli, A. C., Asoh, S. and Nirenberg, M.
(1996), Cloning and characterization of four murine homeobox
genes. Proc. Natl. Acad. Sci. USA
93,10691
-10696.
Schupbach, P. M. (1983). Experimental induction of an incomplete hard-palate cleft in the rat. Oral Surg. Oral Med. Oral Pathol. 55,2 -9.[CrossRef][Medline]
Semina, E. V., Reiter, R., Leysens, N. J., Alward, W. L., Small, K. W., Datson, N. A., Siegel-Bartelt, J., Bierke-Nelson, D., Bitoun, P., Zabel, B. U. et al. (1996). Cloning and characterization of a novel bicoid-related homeobox transcription factor gene, RIEG, involved in Rieger syndrome. Nat. Genet. 14,392 -399.[CrossRef][Medline]
Semina, E. V., Reiter, R. S. and Murray, J. C.
(1998). A new human homeobox gene OGI2X is a member of
the most conserved homeobox gene family and is expressed during heart
development in mouse. Hum. Mol. Genet.
7, 415-422.
Shears, D. J., Vassal, H. J., Goodman, F. R., Palmer, R. W., Reardon, W., Superti-Furga, A., Scamber, P. J. and Winter, R. M. (1998). Mutation and deletion of the pseudoautosomal gene SHOX cause Lòri-Weill dyschondrosteosis. Nat. Genet. 19, 70-73.[CrossRef][Medline]
Shprintzen, R. J. (2002). Terminology and classification of facial clefting. In Understanding Craniofacial Anomalities: The Etiopathogenesis of Craniosynostoses and Facial Clefting (ed. M. P. Mooney and M. I. Siegel), pp.17 -28.New York: Wiley-Liss.
Slavkin, H. C. (1984). Morphogenesis of a complex organ: vertebrate palate development. Curr. Top. Dev. Biol. 19,1 -16.
Small, K. W., Stalvey, M., Fisher, L., Mullen, L., Dickel, C., Beadles, K., Reimer, R., Lessner, A., Lewis, K. and Pericak-Vance, M. A. (1995). Blepharophimosis syndrome is linked to chromosome 3q. Hum. Mol. Genet. 4,443 -448.[Abstract]
Sperber, G. H. (2001). Craniofacial Development. Hamilton. Ontario: BC Decker.
Thesleff, I., Vaahtokari, I. and Partanen, A.-M. (1995). Regulation of organogenesis: Common molecular mechanisms regulating the development of teeth and other organs. Int. J. Dev. Biol. 39,35 -50.[Medline]
Thyagarajan, T., Totey, S., Danton, M. J. and Kulkarni, A.
B. (2003). Genetically altered mouse models: the good, the
bad, and the ugly. Crit. Rev. Oral Biol. Med.
14,154
-174.
Tonkin, E. T., Wang, T. J., Lisgo, S., Bamshad, M. J. and Strachan, T. (2004). NIPBL, encoding a homolog of fungal Scc2-type sister chromatid cohesion protein and fly Nipped-B, is mutated in Cornelia de Lange syndrome. Nat. Genet. 36,636 -641.[CrossRef][Medline]
Van den Boogaard, M.-J. H., Dorland, M., Beemer, F. A. and van Amstel, H. K. P. (2000). MSX1 mutation is associated with orofacial clefting and tooth agenesis in human. Nat. Genet. 24,342 -343.[CrossRef][Medline]
Vastardis, H., Karimbux, N., Guthua, S. W., Seidman, J. G. and Seidman, C. E. (1996). A human MSX1 homeodomain missense mutation causes selective tooth agenesis. Nat. Genet. 13,417 -421.[CrossRef][Medline]
Zhang, Y., Zhao, X., Hu, Y., St Amand, T., Zhang, M., Ramamurthy, R., Qiu, M. and Chen, Y. P. (1999). Msx1 is required for the induction of Patched by Sonic hedgehog in the mammalian tooth germ. Dev. Dyn. 215, 45-53.[CrossRef][Medline]
Zhang, Y., Zhang, Z., Zhao, X., Yu, X., Hu, Y., Geronimo, B.,
Fromm, S. H. and Chen, Y. P. (2000). A new function of BMP4:
dual role for BMP4 in regulation of Sonic hedgehog expression in the
mouse tooth germ. Development
127,1431
-1443.
Zhang, Z., Song, Y., Zhao, X., Zhang, X., Fermin, C. and Chen,
Y. P. (2002). Rescue of cleft palate in
Msx1-deficient mice by transgenic Bmp4 reveals a network of
BMP and Shh signaling in the regulation of mammalian palatogenesis.
Development 129,4135
-4146.
Zhao, X., Zhang, Z., Song, Y., Zhang, X., Zhang, Y., Hu, Y., Fromm, S. H. and Chen, Y. P. (2000). Transgenically ectopic expression of Bmp4 to Msx1 mutant dental mesenchyme restores downstream gene expression but represses Shh and Bmp2 in the enamel knot of wild type tooth germ. Mech. Dev. 99, 29-38.[CrossRef][Medline]
Zhao, Y., Guo, Y. J., Tomac, A. C., Taylor, N. R., Grinberg, A.,
Lee, E. J., Huang, S. and Westphal, H. (1999), Isolated cleft
palate in mice with a targeted mutation of the LIM homeobox gene
Lhx8. Proc. Natl. Acad. Sci. USA
96,15002
-15006.
|