Previous Article | Next Article 
Molecular and Cellular Biology, July 2001, p. 4391-4398, Vol. 21, No. 13
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.13.4391-4398.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Nkx2.5 and Nkx2.6, Homologs of
Drosophila tinman, Are Required for Development of the
Pharynx
Makoto
Tanaka,
Martina
Schinke,
Hai-Sun
Liao,
Naohito
Yamasaki, and
Seigo
Izumo*
Cardiovascular Division, Beth Israel
Deaconess Medical Center, and Department of Medicine, Harvard
Medical School, Boston, Massachusetts 02215
Received 22 January 2001/Returned for modification 1 March
2001/Accepted 23 March 2001
 |
ABSTRACT |
Nkx2.5 and Nkx2.6 are murine homologs of Drosophila
tinman. Their genes are expressed in the ventral region of the pharynx at early stages of embryogenesis. However, no abnormalities in the
pharynges of embryos with mutations in either Nkx2.5 or Nkx2.6 have
been reported. To examine the function of Nkx2.5 and Nkx2.6 in the
formation of the pharynx, we generated and analyzed Nkx2.5 and Nkx2.6
double-mutant mice. Interestingly, in the double-mutant embryos, the
pharynx did not form properly. Pharyngeal endodermal cells were largely
missing, and the mutant pharynx was markedly dilated. Moreover, we
observed enhanced apoptosis and reduced proliferation in pharyngeal
endodermal cells of the double-mutant embryos. These results
demonstrated a critical role of the NK-2 homeobox genes in the
differentiation, proliferation, and survival of pharyngeal endodermal
cells. Furthermore, the development of the atrium was less advanced in
the double-mutant embryos, indicating that these two genes are
essential for both pharyngeal and cardiac development.
| |
INTRODUCTION |
The Nkx2.5 and Nkx2.6 genes are
members of the NK-2 homeobox gene family and are closely related to the
Drosophila tinman gene (2, 5, 21). At early
stages of embryogenesis, Nkx2.5 is expressed in myocardium and
pharyngeal endoderm (6, 7), while Nkx2.6 expression can be
observed in pharyngeal endoderm, sinus venosa, and myocardium of the
outflow tract (1, 12). In the pharynx, both Nkx2.5 and
Nkx2.6 are expressed in the ventral region between embryonic day 8 (E8.0) and E8.5 (1, 7). However, by E9.0, Nkx2.6
expression becomes restricted to the lateral side of the pharynx, the
pharyngeal pouches, while Nkx2.5 is still expressed on the ventral side
of the pharynx, the pharyngeal floor (1, 7, 22). In the
heart, redundant expression of Nkx2.5 and Nkx2.6 has been observed in
the sinus venosa at E8.5 and in the outflow tract at E9.5 (1,
7). Inactivation of Nkx2.5 arrested heart formation at the
looping stage, revealing a critical role of this gene at early stages
of cardiac development (9, 20). However, no abnormalities
in the pharynges of Nkx2.5
/ embryos were reported
(9, 20). Moreover, targeted disruption of Nkx2.6 did not
cause any abnormalities either in the pharynx or in the heart
(22). However, interestingly, in Nkx2.6/
embryos, expression of Nkx2.5 extended to the lateral side of the
pharynx, suggesting a compensatory function of Nkx2.5 in the forming
pharynx (22).
To investigate the function of Nkx2.5 and Nkx2.6 in the formation of
the pharynx, we generated and analyzed Nkx2.5 and Nkx2.6 double-mutant
mice. Interestingly, in the double-mutant embryos, the numbers of
pharyngeal endodermal cells were severely reduced and the pharynges
were markedly dilated, suggesting critical roles of Nkx2.5 and Nkx2.6
in pharyngeal development.
| |
MATERIALS AND METHODS |
Generation of Nkx2.5/ Nkx2.6/
mice.
The generation and viability of Nkx2.5 and Nkx2.6 knockout
mice have been described previously (20, 22). The
bacterial LacZ gene was inserted into the Nkx2.5 locus
(20). Homozygous mutations of Nkx2.5
(Nkx2.5/ mice) were embryonically lethal, while
heterozygous Nkx2.5 mutant mice (Nkx2.5+/ mice) and
homozygous Nkx2.6 mutant mice (Nkx2.6/ mice) were
viable and fertile (20, 22). We first interbred Nkx2.5+/ mice and Nkx2.6/ mice to
generate Nkx2.5+/ Nkx2.6+/ mice mice, and
these in turn were crossed to generate Nkx2.5+/
Nkx2.6/ mice. Nkx2.5+/
Nkx2.6/ mice were viable and fertile.
Nkx2.5+/ Nkx2.6/ mice were then crossed,
and the offspring were genotyped by PCR as previously described
(20). All the mutant mice were maintained in a mixed 129 and C57BL background.
Histological analysis.
Mouse embryos were fixed, dehydrated,
and embedded in paraffin, and in situ hybridization was performed as
previously described (20). Plasmids containing full-length
cDNA for HNF3
and Shh were kindly provided by B. Hogan (Vanderbilt
University Medical School, Nashville, Tenn.). The entire coding region
of Pax9 was a kind gift from H. Peters (Brigham and Women's Hospital,
Boston, Mass.). The plasmids for atrial natriuretic factor (ANF),
B-type natriuretic peptide (BNP), myosin light chain 2A (MLC2A), and MLC2V were described previously (20). Whole-mount
-galactosidase staining was performed according to the method of
Schlaeger et al. (17). TUNEL (terminal
deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling)
staining and immunohistochemistry were performed as previously
described (20).
| |
RESULTS |
Embryonic lethality of the Nkx2.5/
Nkx2.6/ mutation.
We generated
Nkx2.5+/ Nkx2.6/ mice by crossing
compound heterozygotes (Nkx2.5+/ Nkx2.6+/;
see (Materials and Methods). Nkx2.5+/
Nkx2.6/ mice were viable and fertile and exhibited no
detectable abnormalities either in the pharynx or in the heart.
Nkx2.5+/ Nkx2.6/ mice were then
intercrossed, and the offspring were genotyped. As expected, no viable
Nkx2.5/ Nkx2.6/ mice were found.
Morphology and histology of Nkx2.5/
Nkx2.6/ embryos.
To determine the phenotype of
Nkx2.5/ Nkx2.6/ embryos, offspring of
Nkx2.5+/ Nkx2.6/ mice were examined
during development. By E9.5, the expected Mendelian frequency of
homozygous mutants was recovered (Table 1). We first examined
Nkx2.5/ Nkx2.6/ embryos at E9.5 and
E10.5. Nkx2.5/ Nkx2.6/ embryos at E10.5
showed severe growth retardation and massive pericardial effusion (Fig.
1A, and B), looking similar to
Nkx2.5/ embryos (Fig. 1B) (9, 20).
However, histological examination at E9.5 and E10.5 revealed disrupted
formation of the pharynx in Nkx2.5/
Nkx2.6/ embryos (Fig. 1E and H). In wild-type embryos,
the surface of the pharynx was covered with pharyngeal endodermal
cells. A monolayer of endodermal cells covered the pharyngeal roof, and
two or three layers of cuboidal endodermal cells were observed in the
pharyngeal floor and pouches (Fig. 1F). In contrast, in
Nkx2.5/ Nkx2.6/ embryos, the number of
pharyngeal endodermal cells was severely reduced and a continuous
endodermal cell layer was lost. Only a small number of endodermal cells
were observed, mainly on the ventral side (Fig. 1H), and the mutant
pharynx showed severe dilatation (Fig. 1E and H). The abnormal
dilatation was detected only in the pharyngeal part of the foregut
(Fig. 1I to M). Interestingly, Nkx2.5/ embryos also
showed a defect in the pharynx; there were fewer endodermal cells in
the pharyngeal floor and pouches, although the surface of the pharynx
was completely covered by endodermal cells (Fig. 1G).
View larger version (85K):
[in this window]
[in a new window]
|
FIG. 1.
Morphological and histological analysis of
Nkx2.5/ and Nkx2.5/
Nkx2.6/ embryos. (A) Whole-mount -galactosidase
staining of Nkx2.5+/+ Nkx2.6/ and
Nkx2.5/ Nkx2.6/ embryos at E10.5
(littermates) (B) Whole-mount -galactosidase staining of
Nkx2.5/ Nkx2.6/ (left) and
Nkx2.5/ (right) embryos at E10.5. (C to E)
Hematoxylin-and-eosin-stained transverse sections of wild-type (C),
Nkx2.5/ (D), and Nkx2.5/
Nkx2.6/ (E) embryos at E9.5. Note disrupted formation
of the pharynges in Nkx2.5/ Nkx2.6/
embryos. (F to H) Higher-magnification pictures of panels C to E. Note
that a monolayer of endodermal cells remained only in a small region on
the ventral side (between the arrowheads) in Nkx2.5/
Nkx2.6/ embryos. A small number of endodermal cells
also survived in other parts of the pharynx (arrows). (I to M)
Transverse sections of the double-mutant embryo shown in panel B. The
disruption of pharyngeal formation was observed only in the pharyngeal
part of the foregut. Bars, 200 µm.
|
|
To exclude the possibility that the observed defects might be due to
general growth retardation, we analyzed Nkx2.5
/ and
Nkx2.5
/ Nkx2.6
/ embryos at earlier
stages. No growth retardation was detected
in Nkx2.5
/
or Nkx2.5
/ Nkx2.6
/ embryos by E9.0
(Fig.
2A and B). Histological analysis
showed
that the foregut pocket of Nkx2.5
/
Nkx2.6
/ embryos at E8.0 was indistinguishable from that
of wild-type
littermates (Fig.
2C to E). However, at E8.5, pharyngeal
endodermal
cells were lost in some parts of the pharynx and the pharynx
was
abnormally dilated in Nkx2.5
/
Nkx2.6
/ embryos, indicating that the pharyngeal
phenotype was not due
to growth retardation (Fig.
2J). At this stage,
no significant
differences in the pharynx between
Nkx2.5
/ and wild-type embryos were detected (Fig.
2F
and H). However,
at E9.0, the number of pharyngeal endodermal cells was
significantly
lower in Nkx2.5
/ embryos than in
wild-type embryos, suggesting that proliferation
or differentiation of
these cells may be affected by inactivation
of Nkx2.5 (Fig.
2G and L).
View larger version (63K):
[in this window]
[in a new window]
|
FIG. 2.
(A) Wild-type (left), Nkx2.5/ (middle),
and Nkx2.5/ Nkx2.6/ (right) embryos at
E8.5. bar, 1.0 mm. (B) Wild-type (left), Nkx2.5/
(middle), and Nkx2.5/ Nkx2.6/ (right)
embryos at E9.0. Bar, 1.0 mm. (C to E) Histology of the foregut pockets
in hematoxylin-and-eosin-stained wild-type (C), Nkx2.5/
(D), and Nkx2.5/ Nkx2.6/ (E) embryos at
E8.0. Bar, 100 µm. (F to K) Histology of the pharynges in wild-type
(F and G), Nkx2.5/ (H and I), and
Nkx2.5/ Nkx2.6/ (J and K) embryos at
E8.5 (F, H, and J) and E9.0 (G, I, and K). (J and K) A monolayer of
endodermal cells on the ventral side (between the arrowheads) and a few
endodermal cells in other parts (arrows) were observed. Note that a
continuous layer of endodermal cells was already lost and the pharynx
was dilated in Nkx2.5/ Nkx2.6/ embryos
at E8.5.
|
|
Enhanced apoptosis and reduced proliferation of pharyngeal
endodermal cells.
We then examined whether proliferation and/or
apoptosis of pharyngeal endodermal cells was affected by inactivation
of Nkx2.5 and Nkx2.6. TUNEL staining demonstrated that pharyngeal
endodermal cells were largely apoptotic, except for a small number of
cells on the ventral side in Nkx2.5/
Nkx2.6/ embryos (Fig.
3C). There were no differences in the
frequency of apoptotic cells in the pharynx between wild-type and
Nkx2.5/ embryos (Fig. 3A and B), suggesting that
disruption of both Nkx2.5 and Nkx2.6 enhanced apoptosis. We next
performed immunohistochemistry using anti-PCNA (proliferating cell
nuclear antigen) antibody to assess proliferation of pharyngeal
endodermal cells. The rates (means ± standard deviations) of
PCNA-positive cells were 0.71 ± 0.05, 0.43 ± 0.03, and
0.43 ± 0.02 in wild-type, Nkx2.5/, and
Nkx2.5/ Nkx2.6/ embryos, respectively.
(Six sections from three embryos of each group were analyzed. The
differences between wild-type and Nkx2.5/ or
Nkx2.5/ Nkx2.6/ embryos were
significant [P < 0.01].) This result indicated that proliferation of pharyngeal endodermal cells was affected by
inactivation of Nkx2.5.
View larger version (44K):
[in this window]
[in a new window]
|
FIG. 3.
TUNEL staining and PCNA staining. (A to C) TUNEL
staining of transverse sections of wild-type (A),
Nkx2.5/ (B), and Nkx2.5/
Nkx2.6/ (C) embryos at E8.75. Note enhanced apoptosis
in the pharynx of Nkx2.5/ Nkx2.6/
embryos. (D to F) PCNA staining of transverse sections of wild-type
(D), Nkx2.5/ (E), and Nkx2.5/
Nkx2.6/ (F) embryos at E8.75.
|
|
Expression of molecular markers in Nkx2.5/
Nkx2.6/ embryos.
To determine whether
transcription of pharyngeal endoderm-specific genes was affected in
Nkx2.5/ Nkx2.6/ embryos, we performed
in situ hybridization. Hepatocyte nuclear factor 3 (HNF3) is a
winged-helix transcription factor and is expressed in the node,
notochord, floor plate, and embryonic endoderm (23).
Expression of HNF3 was detectable around the pharynx but was
significantly down-regulated in Nkx2.5/ embryos (Fig.
4A and B). Moreover, in the pharynges of
Nkx2.5/ Nkx2.6/ embryos, expression of
HNF3 was lost except for endodermal cells on the ventral side and a
small number of endodermal cells remaining in other parts (Fig. 4C). We
next examined expression of Pax9, which is expressed in the endoderm of
the pharyngeal pouches (15). In wild-type and
Nkx2.5/ embryos, Pax9 expression was observed in the
epithelium of the pharyngeal pouches (Fig. 4D and E). However, in the
pharynges of Nkx2.5/ Nkx2.6/ embryos,
transcripts for Pax9 were not detected (Fig. 4F), indicating that
pharyngeal pouches did not form. Sonic hedgehog (Shh) is a secreted
signaling molecule and is involved in axial patterning, foregut
formation, and distal limb formation (3, 8). In wild-type
embryos, Shh expression was observed in the floor plate, notochord, and
ventral region of the pharyngeal endoderm (Fig. 4G). In
Nkx2.5/ and Nkx2.5/
Nkx2.6/ embryos, expression of Shh in the pharynx was
more restricted but was still detectable (Fig. 4I).
View larger version (88K):
[in this window]
[in a new window]
|
FIG. 4.
Expression of pharyngeal endoderm-specific genes. In
situ hybridization of transverse sections of wild-type and mutant
embryos at E8.75 using probes for the indicated proteins. Bars, 100 µm.
|
|
Phenotype of Nkx2.5/ Nkx2.6+/
embryos.
We crossed Nkx2.5+/ Nkx2.6/
mice and Nkx2.5+/ Nkx2.6+/+ mice to examine
the phenotype of Nkx2.5/ Nkx2.6+/ mice.
Expectedly, the Nkx2.5/ Nkx2.6+/ mutation
was embryonically lethal. However, interestingly,
Nkx2.5/ Nkx2.6+/ embryos at E8.5 and E9.5
exhibited the same phenotype in the pharynx as Nkx2.5/
Nkx2.6/ embryos (Fig.
5A). Expression patterns of HNF3, Shh,
and Pax9 were same as those in Nkx2.5/
Nkx2.6/ embryos (Fig. 5B to D). This result indicated
that one copy of Nkx2.6 in the absence of Nkx2.5 was not sufficient for
the proper formation of the pharynx.
View larger version (121K):
[in this window]
[in a new window]
|
FIG. 5.
Histological analysis of the pharynges of
Nkx2.5/ Nkx2.6+/ embryos. (A) Hematoxylin
and eosin staining of a transverse section at E8.5. (B to D) In situ
hybridization of transverse sections of Nkx2.5/
Nkx2.6+/ embryos at E8.75 using probes for the indicated
proteins. Bars, 100 µm.
|
|
Cardiac phenotype of Nkx2.5/
Nkx2.6/ embryos.
In the course of analyzing mutant
embryos, we noticed a difference in heart morphology in
Nkx2.5/ Nkx2.6/ embryos from
Nkx2.5/ embryos. As described previously, the heart of
Nkx2.5/ embryos lacked endocardial cushion formation
but still had a cleft between the common atrium and ventricle (9,
20) (Fig. 1D). Notably, the distinction between the atrium and
ventricle was less clear and the expansion of the common atrium was
significantly less extensive in the heart of Nkx2.5/
Nkx2.6/ embryos (Fig. 1E). Nkx2.5/
Nkx2.6+/ embryos showed the same cardiac phenotype (data
not shown).
We next investigated alterations in cardiac gene expression in
Nkx2.5
/ Nkx2.6
/ embryos. Expression of
ANF and BNP was observed in both the atrium
and ventricle of wild-type
embryos (Fig.
6A and C). In
Nkx2.5
/ embryos, although expression of these genes in
the ventricle
was abolished, the atrial expression of ANF and BNP was
still
maintained (
20). Interestingly, in
Nkx2.5
/ Nkx2.6
/ embryos, expression of
ANF and BNP in the atrium was also down-regulated.
These genes were
expressed only in a restricted region close to
the atrioventricular
canal (Fig.
6B and D). To assess the specification
of the atrium and
ventricle in Nkx2.5
/ Nkx2.6
/ embryos,
we examined expression of MLC2A and MLC2V. In Nkx2.5
/
Nkx2.6
/ embryos. MLC2A was expressed in the atrium and
ventricle and
MLC2V was expressed only in the ventricle, albeit at a
lower level,
similar to results for Nkx2.5
/ embryos
(
20) (Fig.
6E to H). This result indicated that the
differentiation of atrial myocytes was less advanced but that
the
specification of the atrium and ventricle occurred normally
in
Nkx2.5
/ Nkx2.6
/ embryos.
View larger version (85K):
[in this window]
[in a new window]
|
FIG. 6.
Expression of cardiac tissue-specific genes. In situ
hybridization of transverse sections of wild-type and
Nkx2.5/ Nkx2.6/ embryos at E8.75 using
probes for the indicated proteins. Bars, 100 µm.
|
|
| |
DISCUSSION |
In this study, we demonstrated critical roles of the NK-2 homeobox
genes Nkx2.5 and Nkx2.6 in pharyngeal development using a genetic
approach. At the beginning of the embryonic period, cephalocaudal and
lateral folding of the embryo incorporates the dorsal part of the
endoderm-lined yolk sac into the embryo to form the primitive gut. The
pharyngeal gut, or the pharynx, is the cephalic region of the primitive
gut, extending from the buccopharyngeal membrane to the
tracheobronchial diverticulum. The internal aspect of the pharynx is
lined with epithelial endodermal cells, and a number of diverticula
called pharyngeal pouches appear along the lateral wall of the pharynx
(10). Although hoxa3 and Pax9 have been shown to be
required for the normal development of pharyngeal pouch derivatives
(4, 15), little is known about molecular mechanisms
controlling pharyngeal development.
The ectopic expression of Nkx2.5 in pharyngeal pouches of
Nkx2.6/ embryos suggested a compensatory function of
Nkx2.5 (22). Interestingly, in the double-mutant embryos,
pharyngeal pouches did not form. Therefore, it is possible that
inactivation of both Nkx2.5 and Nkx2.6 has eliminated overlapping
functions of these genes in pharyngeal pouches. In the pharyngeal
floors of Nkx2.5/ embryos, the numbers of endodermal
cells were reduced and significantly fewer PCNA-positive cells were
observed, indicating a critical role of Nkx2.5 in proliferation of
pharyngeal endodermal cells. Moreover, there were only a few endodermal
cells remaining in the pharynges of Nkx2.5/
Nkx2.6/ embryos. Notably, we found markedly enhanced
apoptosis in the pharynges of the double mutant embryos, revealing
overlapping functions of Nkx2.5 and Nkx2.6 in survival of pharyngeal
endodermal cells. However, neither of these genes is expressed in the
pharyngeal roof. Endodermal cells expressing Nkx2.5 and Nkx2.6 on the
ventral side of the pharynx may secrete a signal molecule(s) essential for the maintenance of pharyngeal endodermal cells. Taken together, the
data show that pharyngeal endodermal cells were induced and specified
but could not proliferate and survive in the absence of Nkx2.5 and
Nkx2.6. The abnormal dilatation of the pharynx could be due to the
absence of the epithelial lining in the mutant pharynx. A small number
of nonapoptotic cells expressing Shh in the ventral regions of
Nkx2.5/ Nkx2.6/ embryos remain to be
characterized. These cells may derive from a different cell lineage
from that of other pharyngeal epithelial cells.
The severe down-regulation of ANF and BNP expression in the atrium
suggested that the cardiac program in the atrium is less advanced in
Nkx2.5/ Nkx2.6/ embryos, although the
specification of the atrium and ventricle appeared to be normal. Since
Nkx2.6 is not expressed in the atrium, it is possible that the absence
or down-regulation of a secreted factor(s) from the pharyngeal endoderm
might have caused this cardiac abnormality. This hypothesis is in line
with previous studies showing that signals from the pharyngeal endoderm
were required for differentiation of cardiac myocytes as well as
specification of the cardiac cell lineage (11, 18, 19).
Interestingly, Nkx2.5/ Nkx2.6+/ embryos
showed the same phenotype as Nkx2.5/
Nkx2.6/ embryos. A similar dose-dependent requirement
of transcription factors was shown in the developmental program of the
skeletal muscle. Gene targeting experiments showed that
Myf-5+/ MyoD/ as well as
Myf-5/ MyoD/ mutations were lethal,
implying that two functional copies of Myf-5 were required to rescue
MyoD/ mice (16).
In Caenorhabditis elegans, there is no heart, but pharyngeal
muscle is of mesodermal origin and contracts rhythmically like vertebrate cardiac muscle. Moreover, Ceh22, a homolog of tinman in
C. elegans, is expressed in the pharyngeal muscle and
transactivates several pharynx specific genes (13, 14).
Thus, it has been suggested that functions and development of
pharyngeal muscle in C. elegans may be similar to those of
cardiac muscle in higher organisms. The result that the murine homologs
of tinman were critical for both pharyngeal and cardiac development
support the hypothesis that the vertebrate heart and pharynx may share
a common developmental program.
| |
ACKNOWLEDGMENTS |
We thank B. Hogan and H. Peters for providing plasmids.
This work was supported by an NIH grant to S.I.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: SL-201, Beth
Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215. Phone: (617) 667-4858. Fax: (617) 975-5268. E-mail:
sizumo{at}caregroup.harvard.edu.
Present address: Department of Geriatric Medicine, Graduate School
of Medicine, Kyoto University, Kyoto 606-8507, Japan.
| |
REFERENCES |
| 1.
|
Biben, C.,
T. Hatzistavrou, and R. P. Harvey.
1998.
Expression of NK-2 class homeobox gene Nkx2-6 in foregut endoderm and heart.
Mech. Dev.
73:125-127[CrossRef][Medline].
|
| 2.
|
Bodmer, R.
1993.
The gene tinman is required for specification of the heart and visceral muscles in Drosophila.
Development
118:719-729[Abstract].
|
| 3.
|
Chiang, C.,
Y. Litingtung,
E. Lee,
K. E. Young,
J. L. Corden,
H. Westphal, and P. A. Beachy.
1996.
Cyclopia and defective axial patterning in mice lacking Sonic hedgehog gene function.
Nature
383:407-413[CrossRef][Medline].
|
| 4.
|
Chisaka, O., and M. R. Capecchi.
1991.
Regionally restricted developmental defects resulting from targeted disruption of the mouse homeobox gene hox-1.5.
Nature
350:473-479[CrossRef][Medline].
|
| 5.
|
Harvey, R. P.
1996.
NK-2 homeobox genes and heart development.
Dev. Biol.
178:203-216[CrossRef][Medline].
|
| 6.
|
Komuro, I., and S. Izumo.
1993.
Csx: a murine homeobox-containing gene specifically expressed in the developing heart.
Proc. Natl. Acad. Sci. USA
90:8145-8149[Abstract/Free Full Text].
|
| 7.
|
Lints, T. J.,
L. M. Parsons,
L. Hartley,
I. Lyons, and R. P. Harvey.
1993.
Nkx-2.5: a novel murine homeobox gene expressed in early heart progenitor cells and their myogenic descendants.
Development
119:969[Free Full Text].
|
| 8.
|
Litingtung, Y.,
L. Lei,
H. Westphal, and C. Chiang.
1998.
Sonic hedgehog is essential to foregut development.
Nat. Genet.
20:58-61[CrossRef][Medline].
|
| 9.
|
Lyons, I.,
L. M. Parsons,
L. Hartley,
R. Li,
J. E. Andrews,
L. Robb, and R. P. Harvey.
1995.
Myogenic and morphogenetic defects in the heart tubes of murine embryos lacking the homeo box gene Nkx2-5.
Genes Dev.
9:1654-1666[Abstract/Free Full Text].
|
| 10.
|
Moore, K., and T. Persaud.
1998.
The developing human, 215-256. W. B.
Saunders Company, Philadelphia, Pa.
|
| 11.
|
Nascone, N., and M. Mercola.
1995.
An inductive role for the endoderm in Xenopus cardiogenesis.
Development
121:515-523[Abstract].
|
| 12.
|
Nikolova, M.,
X. Chen, and T. Lufkin.
1997.
Nkx2.6 expression is transiently and specifically restricted to the branchial region of pharyngeal-stage mouse embryos.
Mech. Dev.
69:215-218[CrossRef][Medline].
|
| 13.
|
Okkema, P. G., and A. Fire.
1994.
The Caenorhabditis elegans NK-2 class homeoprotein CEH-22 is involved in combinatorial activation of gene expression in pharyngeal muscle.
Development
120:2175-2186[Abstract].
|
| 14.
|
Okkema, P. G.,
E. Ha,
C. Haun,
W. Chen, and A. Fire.
1997.
The Caenorhabditis elegans NK-2 homeobox gene ceh-22 activates pharyngeal muscle gene expression in combination with pha-1 and is required for normal pharyngeal development.
Development
124:3965-3973[Abstract].
|
| 15.
|
Peters, H.,
A. Neubuser,
K. Kratochwil, and R. Balling.
1998.
Pax9-deficient mice lack pharyngeal pouch derivatives and teeth and exhibit craniofacial and limb abnormalities.
Genes Dev.
12:2735-2747[Abstract/Free Full Text].
|
| 16.
|
Rudnicki, M. A.,
P. N. Schnegelsberg,
R. H. Stead,
T. Braun,
H. H. Arnold, and R. Jaenisch.
1993.
MyoD or Myf-5 is required for the formation of skeletal muscle.
Cell
75:1351-1359[CrossRef][Medline].
|
| 17.
|
Schlaeger, T. M.,
Y. Qin,
Y. Fujiwara,
J. Magram, and T. N. Sato.
1995.
Vascular endothelial cell lineage-specific promoter in transgenic mice.
Development
121:1089-1098[Abstract].
|
| 18.
|
Schultheiss, T. M.,
S. Xydas, and A. B. Lassar.
1995.
Induction of avian cardiac myogenesis by anterior endoderm.
Development
121:4203-4214[Abstract].
|
| 19.
|
Sugi, Y., and J. Lough.
1994.
Anterior endoderm is a specific effector of terminal cardiac myocyte differentiation of cells from the embryonic heart forming region.
Dev. Dyn.
200:155-162[Medline].
|
| 20.
|
Tanaka, M.,
Z. Chen,
S. Bartunkova,
N. Yamasaki, and S. Izumo.
1999.
The cardiac homeobox gene Csx/Nkx2.5 lies genetically upstream of multiple genes essential for heart development.
Development
126:1269-1280[Abstract].
|
| 21.
|
Tanaka, M.,
H. Kasahara,
S. Bartunkova,
M. Schinke,
I. Komuro,
H. Inagaki,
Y. Lee,
G. E. Lyons, and S. Izumo.
1998.
Vertebrate homologs of tinman and bagpipe: roles of the homeobox genes in cardiovascular development.
Dev. Genet.
22:239-249[CrossRef][Medline].
|
| 22.
|
Tanaka, M.,
N. Yamasaki, and S. Izumo.
2000.
Phenotypic characterization of the murine Nkx2.6 homeobox gene by gene targeting.
Mol. Cell. Biol.
20:2874-2879[Abstract/Free Full Text].
|
| 23.
|
Weinstein, D. C.,
A. Ruiz i Altaba,
W. S. Chen,
P. Hoodless,
V. R. Prezioso,
T. M. Jessell, and J. E. Darnell, Jr.
1994.
The winged-helix transcription factor HNF-3 beta is required for notochord development in the mouse embryo.
Cell
78:575-588[CrossRef][Medline].
|
Molecular and Cellular Biology, July 2001, p. 4391-4398, Vol. 21, No. 13
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.13.4391-4398.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
This article has been cited by other articles:
-
Qian, L., Mohapatra, B., Akasaka, T., Liu, J., Ocorr, K., Towbin, J. A., Bodmer, R.
(2008). Transcription factor neuromancer/TBX20 is required for cardiac function in Drosophila with implications for human heart disease. Proc. Natl. Acad. Sci. USA
105: 19833-19838
[Abstract]
[Full Text]
-
Dentice, M., Cordeddu, V., Rosica, A., Ferrara, A. M., Santarpia, L., Salvatore, D., Chiovato, L., Perri, A., Moschini, L., Fazzini, C., Olivieri, A., Costa, P., Stoppioni, V., Baserga, M., De Felice, M., Sorcini, M., Fenzi, G., Di Lauro, R., Tartaglia, M., Macchia, P. E.
(2006). Missense Mutation in the Transcription Factor NKX2-5: A Novel Molecular Event in the Pathogenesis of Thyroid Dysgenesis. J. Clin. Endocrinol. Metab.
91: 1428-1433
[Abstract]
[Full Text]
-
Inga, A., Reamon-Buettner, S. M., Borlak, J., Resnick, M. A.
(2005). Functional dissection of sequence-specific NKX2-5 DNA binding domain mutations associated with human heart septation defects using a yeast-based system. Hum Mol Genet
14: 1965-1975
[Abstract]
[Full Text]
-
Heathcote, K., Braybrook, C., Abushaban, L., Guy, M., Khetyar, M. E., Patton, M. A., Carter, N. D., Scambler, P. J., Syrris, P.
(2005). Common arterial trunk associated with a homeodomain mutation of NKX2.6. Hum Mol Genet
14: 585-593
[Abstract]
[Full Text]
-
De Felice, M., Di Lauro, R.
(2004). Thyroid Development and Its Disorders: Genetics and Molecular Mechanisms. Endocr. Rev.
25: 722-746
[Abstract]
[Full Text]
-
Wang, L.-H., Chmelik, R., Nirenberg, M.
(2002). Sequence-specific DNA binding by the vnd/NK-2 homeodomain of Drosophila. Proc. Natl. Acad. Sci. USA
99: 12721-12726
[Abstract]
[Full Text]
-
Zaffran, S., Frasch, M.
(2002). Early Signals in Cardiac Development. Circ. Res.
91: 457-469
[Abstract]
[Full Text]
-
Bruneau, B. G.
(2002). Transcriptional Regulation of Vertebrate Cardiac Morphogenesis. Circ. Res.
90: 509-519
[Abstract]
[Full Text]
-
HARVEY, R.P., LAI, D., ELLIOTT, D., BIBEN, C., SOLLOWAY, M., PRALL, O., STENNARD, F., SCHINDELER, A., GROVES, N., LAVULO, L., HYUN, C., YEOH, T., COSTA, M., FURTADO, M., KIRK, E.
(2002). Homeodomain Factor Nkx2-5 in Heart Development and Disease. Cold Spring Harb Symp Quant Biol
67: 107-114
[Abstract]
Top
Abstract
Introduction
