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Molecular and Cellular Biology, April 2000, p. 2874-2879, Vol. 20, No. 8
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Phenotypic Characterization of the Murine
Nkx2.6 Homeobox Gene by Gene Targeting
Makoto
Tanaka,
Naohito
Yamasaki, and
Seigo
Izumo*
Cardiovascular Division, Beth Israel
Deaconess Medical Center, and Department of Medicine, Harvard
Medical School, Boston, Massachusetts 02215
Received 21 July 1999/Returned for modification 13 September
1999/Accepted 16 December 1999
 |
ABSTRACT |
The NK-2 homeobox genes have been shown to play critical roles in
the development of specific organs and tissues. Nkx2.6 is a member of
the NK-2 homeobox gene family and is most closely related to the
Drosophila tinman gene. Nkx2.6 is expressed in the caudal
pharyngeal pouches, the caudal heart progenitors, the sinus venosus,
and the outflow tract of the heart and in a short segment of the gut at
early stages of embryogenesis. To investigate the function of Nkx2.6 in
vivo, we generated mice with null mutations of Nkx2.6 by the gene
targeting technique. Homozygous Nkx2.6 mutant mice were viable and
fertile. There were no obvious abnormalities in the caudal pharyngeal
pouch derivatives (the thymus, parathyroid glands, and thyroid gland),
heart, and gut. Expression of Nkx2.6 overlaps that of Nkx2.5 in the
pharynx and heart and that of Nkx2.3 in the pharynx. Interestingly, in
mutant embryos homozygous for Nkx2.6, Nkx2.5 expression extended to the
lateral side of the pharynx, suggesting a compensatory function of
Nkx2.5 in the mutant pharyngeal pouches.
| |
INTRODUCTION |
The NK-2 family genes are a
divergent class of homeobox transcription factors. Four NK genes, NK-1
to -4, were first isolated in Drosophila (10),
and later these genes were classified into two groups, the NK-1 and
NK-2 families (4). The products of the NK-2 family genes
have a characteristic tyrosine at position 54 of the homeodomain, and
the products of most members also contain two other conserved domains,
the TN domain, near the amino terminus, and the NK-2-specific domain,
just carboxy terminal to the homeodomain (6). The NK-2 gene
family, containing Drosophila NK-2, -3, and -4, now
comprises human, mouse, rat, chicken, Xenopus zebra fish,
Caenorhabditis elegans, leech, and planaria genes (5, 6, 17).
So far, nine different NK-2 genes have been isolated in mice. Nkx2.1,
also known as TTF1 or T/ebp, is expressed in the thyroid anlage, the
fetal bronchial epithelium, and the restricted region of the forebrain
(13). It was shown by gene targeting that this gene was
required for formation of the lung, thyroid gland, pituitary gland, and
ventral forebrain (11). Nkx2.2 is expressed in the ventral
forebrain at early stages of development (21), and later on
Nkx2.2 expression is observed in the pancreatic bud and 
cells in
the pancreas (24). Homozygous Nkx2.2 mutant mice showed
abnormal ventral neuronal patterning at early stages. At a neonatal
stage, these mice developed marked hyperglycemia due to a lack of cells in the pancreas (24). Nkx2.3 is expressed in gut
mesenchyme, the epithelium of branchial arches, and the spleen during
development (19). Disruption of Nkx2.3 by gene targeting
caused abnormal development of the small intestine and spleen
(20). Nkx2.5 (also called Csx) starts to be expressed in the
cardiac crescent and continues to be expressed in the myocardium during
development and in the adult (12, 14). Null mutation of
Nkx2.5 arrested heart formation at the looping stage (15,
25), and heterozygous mutations of human Nkx2.5 were shown to
cause familial atrial septal defect and atrioventricular conduction
delays (23).
Nkx2.6 (also called Tix) is a member of the NK-2 gene family and is
closely related to the Drosophila tinman gene in terms of
the homeodomain sequence and the genomic organization (1, 6,
26). Nkx2.6 is expressed in the caudal pharyngeal pouches, restricted regions of the gut endoderm, the sinus venosus, and the
outflow tract of the developing heart (2, 18, 26). To
examine the function of Nkx2.6 in vivo, we generated mice with a null
mutation of Nkx2.6 by gene targeting. Surprisingly, homozygous mutant
mice showed no obvious defects, raising the possibility of redundant
functions of NK-2 genes in these regions.
| |
MATERIALS AND METHODS |
Gene targeting.
An Nkx2.6 genomic clone was isolated
from a mouse 129Sv genomic library using a genomic fragment containing
exon 2 of Nkx2.6 (26). A 5.0-kb upstream fragment containing
5' flanking sequence, the first exon, and part of the intron and a
2.5-kb downstream fragment were ligated into pPNT (27). R1
embryonic stem (ES) cells (16) were cultured on mouse
embryonic fibroblast feeder layers in high-glucose Dulbecco's modified
Eagle medium containing 15% fetal calf serum and 103 U of
leukemia inhibitory factor per ml. ES cells were electroporated with 30 µg of the targeting vector and were cultured on neomycin-resistant mouse embryonic fibroblast feeders with 300 µg of G418 per ml and 2 µM ganciclovir for 7 days. Forty-three drug-resistant colonies were
picked up and genotyped by Southern blotting. Four correctly targeted
clones were obtained, and two of them were injected into blastocysts
from C57BL/6J mice. Male chimeric mice were bred with female C57BL/6J
mice to test for germ line transmission.
Genotyping of progeny.
DNA was isolated from yolk sacs or
tail biopsy specimens of weaned mice. PCR was performed to genotype
embryos and mice. Results of PCR assays were confirmed by Southern blot
analysis. The primers used for detection of the wild-type allele were
5'-GCATCCGTGTTTGTGAAGTGTG-3' and
5'-TGTGGCTTTTGTACCCTCCAGAG-3'. Primers
5'-GCATCCGTGTTTGTGAAGTGTG-3' and
5'-TTCCTGACTAGGGGAGGAGTAGAAG-3' were used to detect the
targeted allele.
Histological analysis.
Tissues were fixed with 4%
paraformaldehyde at 4°C overnight, dehydrated through graded ethanol
and xylene, and embedded in paraffin wax. In situ hybridization was
performed as described previously (25). Whole-mount in situ
hybridization was performed using a digoxigenin-labeled RNA probe as
described previously (7). The Nkx2.5 and Nkx2.6 probes
comprised nucleotides 313 to 648 (14) and 146 to 360 (2), respectively. They were subcloned into pBluescript
(Stratagene, La Jolla, Calif.) and transcribed using T7 RNA polymerase
(Promega, Madison, Wis.). Sense riboprobes for Nkx2.5 and Nkx2.6 gave
no signals (data not shown). The entire coding region of Pax9, kindly
provided by H. Peters (Brigham and Women's Hospital, Boston, Mass.),
was subcloned into pBluescript and transcribed using T7 RNA polymerase.
Probes for the atrial natriuretic factor (ANF), brain natriuretic
peptide (BNP), and myosin light chain 2V (MLC2V) were described
previously (25).
| |
RESULTS |
Generation of Nkx2.6 mutant mice.
To inactivate
Nkx2.6, we constructed a replacement vector that would result in
deletion of the entire second exon, encoding the homeodomain and
NK-2-specific domain (Fig. 1A). After
electroporation and drug selection, 43 drug-resistant colonies were
obtained. Southern blot analysis identified four independent clones
that had been correctly targeted at the Nkx2.6 locus (Fig. 1B). All of
the four clones contained a single integration of the targeting vector,
as demonstrated by Southern blotting with a neo probe (data
not shown). Two clones with homologous recombination were injected into
blastocysts from C57BL/6J mice, and both of them transmitted the
targeted allele through the germ line. The two lines of mutant mice
showed the same phenotype.
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FIG. 1.
Gene targeting of Nkx2.6. (A) The Nkx2.6 genomic locus
and the structure of the targeting vector are shown. Homologous
recombination resulted in the replacement of the second exon, which
encodes the homeodomain and the NK-2-specific domain. Spe,
SpeI; Xb, XbaI; Sal, SalI. (B)
Genotyping of ES cell clones. Genomic DNA was digested with
SpeI and analyzed by Southern blotting using the 5' probe
(SpeI-XbaI fragment).
|
|
Analysis of Nkx2.6 mutant mice.
Heterozygous Nkx2.6 mutant
mice exhibited no obvious defects and were fertile. In crosses of
heterozygous mutant mice, mice with all three possible genotypes were
born with normal Mendelian frequency (ratio of +/+ to +/
to / = 61:111:59), indicating that disruption of Nkx2.6 did not cause
embryonic lethality.
It was reported that Nkx2.6 transcripts were detected in embryos
between embryonic day 8.0 (E8.0) and E11.5, but not in later-stage
embryos (
2,
18). Thus, we examined Nkx2.6 expression at the
neonatal stage by in situ hybridization using serial sections
of the
whole neonates. However, we could not detect transcripts
for Nkx2.6 in
any organs or tissues of neonates (data not shown).
We also examined
expression of Nkx2.6 by in situ hybridization
in adult organs, such as
the brain, heart, lung, liver, pancreas,
esophagus, stomach, intestine,
kidney, and adrenal gland, and
in adult skeletal muscle and aorta.
However, we could not observe
Nkx2.6 expression in any adult organs or
tissues examined (data
not shown). Therefore, we focused on the
analysis of the tissues
and organs where Nkx2.6 is expressed at early
stages of
embryogenesis.
We first confirmed the absence of Nkx2.6 transcripts in homozygous
mutant (Nkx2.6
/) embryos by in situ hybridization using
a probe containing the
first and second exons of Nkx2.6. In wild-type
embryos, Nkx2.6
expression was clearly detected in the pharyngeal
pouches (Fig.
2A and B). In contrast, no
transcripts could be detected in Nkx2.6
/ embryos (Fig.
2A and C), indicating that we created mice with
a null mutation of
Nkx2.6.
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FIG. 2.
Absence of Nkx2.6 transcripts in homozygous mutant
embryos. (A) Wild-type (+/+) and homozygous mutant (/) embryos at
E9.5 were analyzed by whole-mount in situ hybridization using an Nkx2.6
probe containing the first and second exons. Note the complete absence
of Nkx2.6 transcripts in the pharynx of the homozygous mutant embryo.
Scale bar = 0.5 mm. (B and C) Tissue sections of wild-type (+/+)
and homozygous mutant (/) embryos at E9.5 were hybridized with the
Nkx2.6 probe. In the wild-type embryo, Nkx2.6 is strongly expressed in
the third and fourth pharyngeal pouches. In contrast, no signals were
detected in the homozygous mutant embryo. m, mandibular component of
the first pharyngeal arch; III and IV, third and fourth pharyngeal
pouches; a, atrium. Scale bars = 100 µm.
|
|
We then performed whole-mount in situ hybridization of wild-type and
Nkx2.6
/ embryos using a Pax9 probe to examine
pharyngeal pouch formation
in mutant embryos. All four pharyngeal
pouches (I to IV) were
present in Nkx2.6
/ embryos (Fig.
3B), as they were in wild-type
littermates (Fig.
3A). We next examined formation of caudal pharyngeal
pouch derivatives.
We could observe normal formation of the thymus and
parathyroid
gland (Fig.
3C and D). The numbers (means ± standard
deviations)
of the chief cells in the parathyroid gland were comparable
in
Nkx2.6
/ and wild-type mice (1,522 ± 168 and
1,536 ± 106, respectively,
per 400× microscopic field, six
sections from two mice of each
group). The parafollicular cells of the
thyroid gland also derive
from caudal pharyngeal pouches. Histological
analysis showed that
parafollicular cells normally exist in the thyroid
gland of Nkx2.6
/ mice (Fig.
3E). There were no
significant differences in the
ratio of parafollicular cells to
follicle epithelial cells between
Nkx2.6
/ and wild-type
mice (0.26 ± 0.05 and 0.27 ± 0.04, respectively,
six
sections from three mice of each group). Moreover, the serum
calcium
levels were comparable in Nkx2.6
/ and wild-type mice
(9.2 ± 0.3 and 9.5 ± 0.5 mg/dl, respectively,
five mice
from each group).
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FIG. 3.
Caudal pharyngeal pouch derivatives normally formed in
homozygous mutant mice. (A and B) Whole-mount in situ hybridization of
wild-type (+/+) and homozygous mutant (/) embryos using a Pax9
probe. The arrowheads show the pharyngeal pouches (I to IV). Scale
bars = 0.5 mm. (C) Normal formation of the thymus in a homozygous
mutant neonate. Hematoxylin and eosin (H&E) staining was used. tm,
thymus. Scale bar = 300 µm. (D) Normal histology of the
parathyroid gland in a homozygous mutant mouse (5 months old). H&E
staining was used. tr, thyroid gland; pt, parathyroid gland. Scale
bar = 100 µm. (E) Parafollicular cells in the mutant thyroid
gland (5 months old), indicated by arrowheads. H&E staining was used.
Scale bar = 50 µm.
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|
We next examined the heart and gut in Nkx2.6
/ mice.
Since Nkx2.6 expression can be detected in caudal heart progenitors at
E8.0, we examined expression of ANF and BNP in the mutant atrium.
However, both ANF and BNP were normally expressed in the atrium
in
Nkx2.6
/ embryos (Fig.
4A and
B). Nkx2.6 is also expressed in the sinus
venosus and in the myocardium of the outflow tract. No abnormalities
were detected in either the superior and inferior venae cavae
(Fig.
4C), the sinus venarum cavum of the right atrium (Fig.
4D),
or the
coronary sinus (data not shown), which are all derived
from the sinus
venosus. We also examined expression of MLC2V,
which marks the
myocardium of the ventricle and the outflow tract
during development,
in Nkx2.6
/ embryos. However, we could observe normal
expression of MLC2V
in the myocardium of the outflow tract in
Nkx2.6
/ embryos (Fig.
4E). There were no abnormalities
in the outflow
tract region, including the pulmonary artery and the
aorta (Fig.
4F), in adult Nkx2.6
/ mice, either. In the
embryonic gut, Nkx2.6 is expressed in a
segment at the foregut-midgut
junction spanning the proximal parts
of the common bile duct and
pancreatic ducts (
2). However,
there were no anatomical
defects in these regions. Moreover, there
were no significant
differences in the serum bilirubin concentration
between
Nkx2.6
/ and wild-type mice (0.2 ± 0.1 and
0.2 ± 0.1 mg/dl, respectively,
six mice from each group).
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FIG. 4.
Normal gene expression and morphology of the heart and
gut in homozygous mutant mice. (A and B) Normal expression of ANF (A)
and BNP (B) in the atria of Nkx2.6/ mice. In situ
hybridization revealed normal expression of ANF and BNP in both the
atria and the ventricles of Nkx2.6/ embryos (E10.5).
ra, right atrium; la, left atrium. Scale bars = 100 µm. (C)
Sinus venosus derivatives in a homozygous mutant mouse (6 months old).
SVC, superior vena cava; IVC, inferior vena cava; sv, sinus venarum
cavum; fo, fossa ovalis. Scale bar = 0.5 mm. (D) Normal expression
of MLC2V in the ventricle and outflow tract in Nkx2.6/
mice. rv, right ventricle; lv, left ventricle; ot, outflow tract. Scale
bar = 100 µm. (E) Normal morphology of the outflow tract in a
homozygous mutant mouse (6 months old). ra, right atrium; ao, aorta;
pa, pulmonary artery; la, left atrium. Scale bar = 1 mm. (F)
Normal formation of the common bile duct (cbd) and the pancreatic duct
(pd) in a homozygous mutant mouse (6 months old). A part of the
pancreatic tissue was removed to show the pancreatic duct. d, duodenum;
p, pancreas. Scale bar = 0.5 mm.
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|
Since Nkx2.3 and Nkx2.5 are expressed in the pharyngeal region
similarly to Nkx2.6, we tested the hypothesis that alterations
in
Nkx2.3 or Nkx2.5 expression may compensate for a loss of Nkx2.6
expression in the pharynx in Nkx2.6
/ mice. Normally,
Nkx2.5 expression is restricted to the ventral
side of the pharynx, the
pharyngeal floor (Fig.
5A).
Interestingly,
however, in Nkx2.6
/ embryos Nkx2.5
expression extended to the lateral side of the
pharynx, where Nkx2.6 is
normally expressed (Fig.
5B and C). These
results suggested that
ectopic expression of Nkx2.5 might compensate
for a loss of Nkx2.6
functions in the mutant pharynx. There were
no differences in
expression of Nkx2.3 between Nkx2.6
/ and wild-type mice
(data not shown).
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FIG. 5.
Expression of Nkx2.5 in Nkx2.6/ embryos.
(A) Expression of Nkx2.5 in a wild-type (WT) embryo at E9.5. Nkx2.5 is
expressed in the pharyngeal floor. Note the absence of Nkx2.5
transcripts in the pharyngeal pouches (arrows). Scale bar = 100 µm. (B and C) Expression of Nkx2.5 in Nkx2.6/ embryos
at E9.5. Note the ectopic expression of Nkx2.5 in pharyngeal pouches
(arrows). Scale bars = 100 µm.
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|
| |
DISCUSSION |
In spite of the intensive analysis, we could not detect
any obvious defects in Nkx2.6/ mice. So far, we have
observed Nkx2.6/ mice for up to 2 years, but they
showed no differences, including in life span. The partially
overlapping expression patterns of the NK-2 genes may have redundant
functions in specific organs and tissues. It is well known that
expression of Hox genes partially overlaps along the anterior-posterior
axis. This expression pattern led to the concept of a "Hox code,"
which means that a particular combination of Hox genes may play
critical roles in specification and formation of particular tissues and
organs (8, 9). Thus, the partially overlapping expression
patterns of the NK-2 genes raises the possibility of an "Nkx code"
(22). Moreover, as shown in this study, alterations in
expression patterns of another NK-2 gene may also work as a
compensatory mechanism. Ectopic expression of Nkx2.5 may make up for a
loss of Nkx2.6 in the mutant pharyngeal pouches.
Interestingly, in gene targeting studies of the NK-2 family genes, not
all sites of expression of the NK-2 genes showed phenotypic alterations. For example, homozygous Nkx2.3 or Nkx2.5 mutant mice showed no obvious abnormalities in the pharynx (15, 20,
25). The gut phenotype of Nkx2.3 mutant mice was confined to the
small intestine (20). Furthermore, disruption of Nkx2.5 did
not abolish the cardiac cell lineage (25), although
tinman mutant flies have no cardiac precursor cells
(3). It would be interesting to examine the effects of
double and triple inactivation of Nkx2.6, Nkx2.3, and Nkx2.5 in vivo.
| |
ACKNOWLEDGMENTS |
We thank I. Komuro and H. Inagaki for the initial isolation of an
Nkx2.6 genomic clone.
This work was supported by a grant from NIH to S.I. M.T. is a Paul
Dudley White Fellow of the American Heart Association, Massachusetts affiliate.
| |
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.
| |
REFERENCES |
| 1.
|
Azpiazu, N., and M. Frasch.
1993.
tinman and bagpipe: two homeo box genes that determine cell fates in the dorsal mesoderm of Drosophila.
Genes Dev.
7:1325-1340[Abstract/Free Full Text].
|
| 2.
|
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].
|
| 3.
|
Bodmer, R.
1993.
The gene tinman is required for specification of the heart and visceral muscles in Drosophila.
Development
118:719-729[Abstract].
|
| 4.
|
Burglin, T. R.
1993.
A comprehensive classification of homeobox genes, p. 25-71.
In
D. Duboule (ed.), Guidebook to the homeobox genes. Oxford University Press, Oxford, England.
|
| 5.
|
Garcia-Fernandez, J.,
J. Baguna, and E. Salo.
1991.
Planarian homeobox genes: cloning, sequence analysis, and expression.
Proc. Natl. Acad. Sci. USA
88:7338-7342[Abstract/Free Full Text].
|
| 6.
|
Harvey, R. P.
1996.
NK-2 homeobox genes and heart development.
Dev. Biol.
178:203-216[CrossRef][Medline].
|
| 7.
|
Hogan, B.,
R. Beddington,
F. Costantini, and E. Lacy.
1994.
Manipulating the mouse embryo: a laboratory manual, p. 352-367.
Cold Spring Harbor Laboratory Press, Plainview, N.Y.
|
| 8.
|
Hunt, P., and R. Krumlauf.
1991.
Deciphering the Hox code: clues to patterning branchial regions of the head.
Cell
66:1075-1078[CrossRef][Medline].
|
| 9.
|
Kessel, M., and P. Gruss.
1991.
Homeotic transformations of murine vertebrae and concomitant alteration of Hox codes induced by retinoic acid.
Cell
67:89-104[CrossRef][Medline].
|
| 10.
|
Kim, Y., and M. Nirenberg.
1989.
Drosophila NK-homeobox genes.
Proc. Natl. Acad. Sci. USA
86:7716-7720[Abstract/Free Full Text].
|
| 11.
|
Kimura, S.,
Y. Hara,
T. Pineau,
P. Fernandez-Salguero,
C. H. Fox,
J. M. Ward, and F. J. Gonzalez.
1996.
The T/ebp null mouse: thyroid-specific enhancer-binding protein is essential for the organogenesis of the thyroid, lung, ventral forebrain, and pituitary.
Genes Dev.
10:60-69[Abstract/Free Full Text].
|
| 12.
|
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].
|
| 13.
|
Lazzaro, D.,
M. Price,
M. de Felice, and R. Di Lauro.
1991.
The transcription factor TTF-1 is expressed at the onset of thyroid and lung morphogenesis and in restricted regions of the foetal brain.
Development
113:1093-1104[Abstract].
|
| 14.
|
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
119:419-431[Abstract].
|
| 15.
|
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].
|
| 16.
|
Nagy, A.,
J. Rossant,
R. Nagy,
W. Abramow-Newerly, and J. C. Roder.
1993.
Derivation of completely cell culture-derived mice from early-passage embryonic stem cells.
Proc. Natl. Acad. Sci. USA
90:8424-8428[Abstract/Free Full Text].
|
| 17.
|
Nardelli-Haefliger, D., and M. Shankland.
1993.
Lox10, a member of the NK-2 homeobox gene class, is expressed in a segmental pattern in the endoderm and in the cephalic nervous system of the leech Helobdella.
Development
118:877-892[Abstract].
|
| 18.
|
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].
|
| 19.
|
Pabst, O.,
A. Schneider,
T. Brand, and H. H. Arnold.
1997.
The mouse Nkx2-3 homeodomain gene is expressed in gut mesenchyme during pre- and postnatal mouse development.
Dev. Dyn.
209:29-35[CrossRef][Medline].
|
| 20.
|
Pabst, O.,
R. Zweigerdt, and H. H. Arnold.
1999.
Targeted disruption of the homeobox transcription factor Nkx2-3 in mice results in postnatal lethality and abnormal development of small intestine and spleen.
Development
126:2215-2225[Abstract].
|
| 21.
|
Price, M.,
D. Lazzaro,
T. Pohl,
M. G. Mattei,
U. Ruther,
J. C. Olivo,
D. Duboule, and R. Di Lauro.
1992.
Regional expression of the homeobox gene Nkx-2.2 in the developing mammalian forebrain.
Neuron
8:241-255[CrossRef][Medline].
|
| 22.
|
Reecy, J. M.,
M. Yamada,
K. Cummings,
D. Sosic,
C. Y. Chen,
G. Eichele,
E. N. Olson, and R. J. Schwartz.
1997.
Chicken Nkx-2.8: a novel homeobox gene expressed in early heart progenitor cells and pharyngeal pouch-2 and -3 endoderm.
Dev. Biol.
188:295-311[CrossRef][Medline].
|
| 23.
|
Schott, J. J.,
D. W. Benson,
C. T. Basson,
W. Pease,
G. M. Silberbach,
J. P. Moak,
B. J. Maron,
C. E. Seidman, and J. G. Seidman.
1998.
Congenital heart disease caused by mutations in the transcription factor NKX2-5.
Science
281:108-111[Abstract/Free Full Text].
|
| 24.
|
Sussel, L.,
J. Kalamaras,
O. C. D. J. Hartigan,
J. J. Meneses,
R. A. Pedersen,
J. L. Rubenstein, and M. S. German.
1998.
Mice lacking the homeodomain transcription factor Nkx2.2 have diabetes due to arrested differentiation of pancreatic beta cells.
Development
125:2213-2221[Abstract].
|
| 25.
|
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].
|
| 26.
|
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].
|
| 27.
|
Tybulewicz, V. L.,
C. E. Crawford,
P. K. Jackson,
R. T. Bronson, and R. C. Mulligan.
1991.
Neonatal lethality and lymphopenia in mice with a homozygous disruption of the c-abl proto-oncogene.
Cell
65:1153-1163[CrossRef][Medline].
|
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Abstract
Introduction
