1 Department of Molecular Genetics and The Institute for Cellular and Molecular
Biology, University of Texas at Austin, Austin, TX 78712, USA
2 Department of Medicine, University of Pennsylvania, Philadelphia, PA 19104,
USA
3 Department of Cell and Developmental Biology, University of Pennsylvania,
Philadelphia, PA 19104, USA
Authors for correspondence (e-mail:
emorrise{at}mail.med.upenn.edu
and
philtucker{at}mail.utexas.edu)
Accepted 27 May 2004
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SUMMARY |
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Key words: Foxp1, Endocardial cushion, Outflow tract, Myocyte proliferation, Mouse
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Introduction |
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Interactions between the endocardium and myocardium are also thought to
play an important role in the differentiation and maturation of cardiac
myocytes. The endocardium lines the trabecular myocardium and is essential for
guiding the differentiation of this tissue. The myocardium exhibits an
increasing gradient of differentiation from the outer compact zone to the
inner trabecular zone. The neuregulin signaling pathway, consisting of the
ErbB receptors and neuregulin ligand, plays an important role in
cardiac myocyte differentiation. Neuregulin is expressed in the endocardium,
while the ErbB receptors are expressed primarily in myocardium
(Carraway, 1996;
Gassmann et al., 1995
;
Kramer et al., 1996
;
Lee et al., 1995
;
Meyer and Birchmeier, 1995
).
Both neuregulin and ErbB4-deficient embryos lack mature trabecular
myocardium, leading to mid-gestation embryonic lethality
(Gassmann et al., 1995
;
Kramer et al., 1996
).
In the myocardium, recent evidence suggests that there are several key
families of factors that regulate cardiac myocyte specific gene transcription
and differentiation, including GATA, MEF, SRF and Nkx factors (reviewed by
Brand, 2003). However, there is
growing evidence that other transcription factor families also regulate
cardiac morphogenesis, including members of the Fox gene family of
winged-helix DNA-binding domain transcription factors
(Kume et al., 2001
;
Yamagishi et al., 2003
).
Fox genes comprise a large family of genes that contain a homologous
DNA-binding domain called either the forkhead or winged-helix DNA-binding
domain (Kaestner et al.,
2000). This DNA-binding domain binds to the consensus sequence
5'-TRTTKRY-3' found in the promoters and enhancers of many genes
(Costa et al., 2001
). Recent
evidence has demonstrated a role for Fox proteins in the regulation of cardiac
development. Foxc1 and Foxc2 are expressed in vascular
smooth muscle, endothelial cells of large blood vessels and the heart, and in
head mesenchyme (Swiderski et al.,
1999
; Winnier et al.,
1999
). Inactivation of either Foxc1 or Foxc2
results in perinatal lethality due to cardiovascular defects, including
coarctation of the aortic arch and ventricular septation defects
(Winnier et al., 1999
).
Interestingly, compound heterozygous Foxc1/c2 mutants also
display similar cardiac defects and die perinatally, suggesting that
Foxc1 and Foxc2 may play similar dose-dependent roles during
cardiac development (Kume et al.,
2001
; Winnier et al.,
1999
). This is supported by a more dramatic cardiac phenotype in
compound homozygous Foxc1/c2 embryos, leading to embryonic
demise at E9.5 (Kume et al.,
2001
). Finally, Foxc1/c2 and Foxa2 are
thought to regulate expression of Tbx1, a gene implicated in
DiGeorge's syndrome, a human genetic disease that causes severe cardiac
developmental defects, including outflow tract and ventricular septation
defects (Yamagishi et al.,
2003
).
We have recently reported the identification of a new subfamily of Fox
genes, Foxp1/2/4. These genes are expressed in overlapping patterns in lung,
neural, lymphoid and cardiac tissues (Lu
et al., 2002; Shu et al.,
2001
; Wang et al.,
2003
). They have been implicated in regulating both lung and
neural development and gene expression
(Ferland et al., 2003
;
Lu et al., 2002
;
Shu et al., 2001
;
Wang et al., 2003
). However, a
role in cardiac development has not been reported for any Foxp family member.
Here, we show that inactivation of Foxp1 results in severe cardiac
defects leading to embryonic death at E14.5. Ventricular and outflow tract
septation, as well as valve formation, are defective in Foxp1 null
embryos. Furthermore, cardiac myocyte proliferation and maturation are
defective in these embryos. These defects indicate a role for Foxp1
in the regulation of cardiac myocyte maturation and proliferation as well as
outflow tract and endocardial cushion development.
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Materials and methods |
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SM1-129SVJ mouse embryonic stem (ES) cells were electroporated with the targeting vector, and correctly targeted clones that survived double selection in G418 and FIAU were identified by Southern blot analysis of genomic DNA. To screen for homologous recombination of the short arm, DNA from each clone was digested with PstI, fractionated by electrophoresis through 0.8% agarose gels, transferred to Nitran+ (Amersham), and hybridized with a 700 bp PstI-PstI genomic fragment residing 3' of the 2.4 kb XhoI-SmaI fragment (3' arm). In wild-type ES cells, the PstI fragment is 3.3 kb; in Foxp1+/ ES cells, the PstI fragments are 3.3 kb (wild type) and 4.9 kb (mutant). For homologous recombination of the long arm (5' arm, DNA was digested with XbaI and probed with a 1.2 kb XhoI-XhoI fragment 5' to the KpnI-PstI fragment. In wild-type ES cells, the hybridized XbaI fragment is 7.5 kb; in Foxp1+/ ES cells, the hybridized XbaI fragments are 7.5 kb (wild type) and 11.5 kb (mutant) (data not shown).
Correctly targeted clones were injected into E3.5 C57BL/6 blastocysts, and the resulting chimeric males were mated to wild-type C57BL/6 females for germline transmission of the altered allele. For these studies, Foxp1+/ mice were backcrossed to C57BL/6 for at least four generations. Routine genotyping of wild-type and altered Foxp1 alleles was done by PCR. The wild-type allele was identified by the production of a 430 bp PCR product when the primer pair 1 (5'-CCTCTGGCGATGAACCTAGTGGTTC-3') and 2 (5'-AGCCACACTTTCTCTCAGGATGTCC-3') was used. The altered Foxp1 allele was identified by the production of a 280 bp PCR product when primer 1 was used with a primer in the neo cassette (5'-AGCGCATGCTCCAGACTGCCTTG-3').
Histological procedures
Embryos were collected at the days post conception as indicated and fixed
in 4% paraformaldehyde for 24-48 hours. Embryos were then dehydrated through a
series of ethanol solutions and were embedded in paraffin. In-situ
hybridization, immunohistochemistry, and TUNEL staining were performed as
previously described (Kuo et al.,
1997; Shu et al.,
2001
). The Anf (Nppa Mouse Genome
Informatics) and N-myc in-situ probes have been previously described
(Kuo et al., 1997
;
Sawai et al., 1993
). The
Irx3 probe consisted of bp 196-711 of the published Irx3
cDNA (Christoffels et al.,
2000
). The p21 (mouse monoclonal, 1:100), p27 (mouse monoclonal,
1:50), and p57 (mouse monoclonal, 1:100) antibodies are from Santa Cruz
Biotechnologies and the phospho-histone H3 antibody (mouse monoclonal, 1:400)
is from Cell Signaling Technologies. The fibronectin antibody (rabbit
polyclonal, 1:100) is from Novus Biologicals. Electron microscopy studies were
performed essentially as described (Kuo et
al., 1997
). Further details on histological procedures can be
found at the University of Pennsylvania Molecular Cardiology Center website:
http://www.uphs.upenn.edu/mcrc/.
To quantify the number of cells showing positive staining for TUNEL, PO4-histone H3, p21, and p27, three different fields of view for three embryos of each indicated genotype and age were viewed at 400X magnification. Positively stained cells were counted and the results are graphically shown ± standard error of the mean.
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Results |
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Foxp1/ embryos examined at E14.5 displayed several signs of cardiovascular failure, including edema and perivascular hemorrhage (Fig. 1E). The heart rate of E13.5 and E14.5 Foxp1/ embryos was slower and more irregular than that of wild-type littermates (data not shown). To determine the cardiovascular defects responsible for the embryonic lethality of Foxp1 null embryos, histological sections were generated from E11.5 and E14.5 wild-type and Foxp1 null embryos (Fig. 2). H+E staining reveals several morphological abnormalities, including obvious ventricular septation defects (VSD) at E14.5 (Fig. 2F). Closer analysis revealed that the compact zone of the ventricular wall was thinner both at E11.5 and E14.5 (Fig. 2). Some areas of the compact zone of the myocardium were only two or three cells thick, suggesting severe defects in myocardial growth and/or differentiation.
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Sox4 expression is significantly reduced in Foxp1 null hearts
In addition to Nfatc1, several other genes expressed in either
mesenchyme or endocardium are known regulators of endocardial cushion and
outflow tract septation development. Sox4 and fibronectin are
expressed primarily in the cushion and valve mesenchyme with lower expression
in the overlying endocardium, while Foxc1 and Foxc2 are
expressed primarily in the overlying endocardium
(Bouchey et al., 1996;
Hiltgen et al., 1996
;
Kume et al., 2001
;
Winnier et al., 1999
;
Ya et al., 1998
). To determine
whether their expression was altered in
Foxp1/ hearts, we carried out either in-situ
hybridization (for Sox4, Foxc1 and Foxc2) or
immunohistochemistry for fibronectin expression
(Fig. 6). A significant
reduction in Sox4 expression was observed in the cushions and
myocardium of the outflow tract at both E11.5 and E14.5
(Fig. 6A-E). Expression of
fibronectin, Foxc1 or Foxc2 was not effected in either
outflow or atrial-ventricular regions in
Foxp1/ hearts
(Fig. 6F-K and data not shown).
Together, these data suggest that Foxp1 may reside upstream of
Sox4 in the same regulatory pathway in cardiac cushion development.
This is supported by the similarities between the cardiac phenotype in
Sox4 and Foxp1 mutant mice, including outflow septation
defects, cushion development defects and DORV
(Ya et al., 1998
).
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Defective myocardial maturation in Foxp1 null hearts
During heart development, myocytes mature to form both compact and
trabecular layers within the ventricular wall (reviewed by
Mikawa and Fischman, 1996).
This maturation process results in changes in cardiac-specific gene
expression. In early cardiac development, Irx3, an iroquois homoeobox
transcription factor, and atrial naturetic factor (Anf; Nppa
Mouse Genome Informatics) are expressed exclusively in trabecular zone
myocytes, while N-myc is expressed exclusively in the compact zone of
the developing heart (Charron et al.,
1992
; Christoffels et al.,
2000
; Sawai et al.,
1993
). To determine whether expression of these genes was altered
in Foxp1 null hearts, we performed in-situ hybridization analysis.
Expression of Irx3 was expanded in Foxp1 null hearts at
E14.5 to encompass both the trabecular and compact zone
(Fig. 8A,B). By contrast,
Anf expression remained unchanged
(Fig. 8C,D). N-myc
expression was significantly reduced in the ventricular walls of
Foxp1 null hearts at E11.5 (Fig.
8E,F) and E14.5 (Fig.
8G,H), which correlates with a thinner compact zone.
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Discussion |
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Formation of the outflow tract of the developing heart is regulated by a
complex series of morphogenetic events. These events are required for proper
septation and alignment of the aorta and pulmonary artery such that the aorta
emerges from the left ventricle and the pulmonary artery emerges from the
right ventricle. Disruptions in this process can lead to a constellation of
congenital defects in humans, such as PTA, DORV, and transposition of the
great vessels (Conway et al.,
2003; Dees and Baldwin,
2002
). However, how this process is regulated at the molecular
level is only recently being unraveled and these defects may represent a
spectrum of phenotypes regulated by common mechanisms. Neural crest cells are
thought to play an important role in the development of the outflow tract of
the heart. Several transcription factors and signaling molecules expressed in
neural crest and endocardium have been implicated in regulating endocardial
cushion and outflow tract development. Endocardial cells migrate into and
populate the cushion mesenchyme, losing expression of many endocardially
specific genes, such as Nfatc1
(Brand, 2003
). Targeted
inactivation of Nfatc1 results in defective outflow tract cushion and
vessel development, which leads to embryonic death
(de la Pompa et al., 1998
).
However, Nfatc1 expression persists in the mesenchyme of
Foxp1 null endocardial cushions at E14.5. This could be due to
defects in EMT or subsequent tissue remodeling events involving apoptosis,
which may eliminate these cells through programmed cell death. The lack of
defects in apoptosis and Nfatc1 expression earlier in development (i.e. E11.5)
in Foxp1/ hearts when EMT is actively
occurring is supportive of a tissue remodeling event rather than a direct
effect on endocardial cushion EMT.
Targeted inactivation of Foxc1, Foxc2 and Sox4 also leads
to embryonic lethality due to defects in cardiac cushion formation and outflow
tract septation (Kume et al.,
2001; Schilham et al.,
1996
; Winnier et al.,
1999
). Sox4 is normally expressed in both cushion
mesenchyme and the overlying endothelial cells in the outflow tract region
(Maschhoff et al., 2003
;
Schilham et al., 1996
;
Ya et al., 1998
). We observed
that Sox4, but not these other factors, is downregulated in
Foxp1/ hearts. This result suggests that
Foxp1 may reside upstream of Sox4 in a molecular pathway
regulating cardiac cushion and outflow tract development. The phenotype in
Sox4 null embryos bears striking similarities to the cardiac defects
in Foxp1 null embryos, including a similar embryonic stage of
lethality, PTA, presence of VSD, defective outflow tract endocardial cushions
development marked by increased cellularity within the cushion mesenchyme, and
double outlet-right ventricle in a subset of embryos
(Ya et al., 1998
). Since
Foxp1 is expressed in cells underlying the cushion mesenchyme only in
early development, direct regulation of Sox4 by Foxp1 in
this tissue would have to occur early. Alternatively, Foxp1 may
regulate Sox4 gene expression in the overlying endocardium. The
reduction in Sox4 expression could also be a secondary result of
defective EMT or other tissue remodeling processes in the endocardial cushions
of Foxp1/ embryos. Tissue-specific
inactivation of Foxp1 will be required to determine which cell type
confers these cushion defects.
Foxp1 and cardiomyocyte proliferation
The increased ratio of trabecular to compact zone myocardium resulting in a
thin ventricular wall probably contributes to defects in ventricular
hemodynamics that lead to embryonic death in
Foxp1/ embryos. Thinning of the ventricular
wall, which is seen in several mouse models with cardiac defects, can be
attributed to non-cell autonomous effects
(Chen et al., 1994;
Schilham et al., 1996
;
Svensson et al., 2000
;
Tevosian et al., 2000
).
However, the high level of Foxp1 expression throughout the myocardium
early in development suggests a cell-autonomous cause for the thin ventricular
compact zone in Foxp1/ embryos. Cell
proliferation in Foxp1/ hearts is aberrantly
regulated as demonstrated by the increase in cell proliferation in the
trabecular zone, a region which normally exhibits little proliferation.
However, trabecular myocardium in Foxp1/
embryos also exhibited increased p21 levels and decreased p27 levels,
suggesting that cell cycle regulation is compromised in a complex manner in
Foxp1 null hearts. One hypothesis is that p21 levels are upregulated
in response to increased proliferation and thus its elevation is secondary to
loss of Foxp1 expression. Alternatively, Foxp1 may
positively regulate p21 expression, but this is insufficient to overcome
decreased p27 levels, which, along with other disruptions in the cell cycle,
lead to increased proliferation. Interestingly, expression of N-myc,
which is known to positively regulate cell proliferation, was reduced in
Foxp1 null hearts, although this reduction could be secondary to an
overall reduction in compact zone development
(Charron et al., 1992
;
Moens et al., 1993
).
The regulation of cell proliferation in cardiac myocytes has been the
subject of much study. As with other terminally differentiated cells, cardiac
myocytes proliferate for a short time in utero and only briefly postnatally
before becoming quiescent. However, the exact cell cycle machinery involved in
regulating embryonic proliferation and keeping mature cardiac myocytes
quiescent is not well defined. Research into this area of myocyte biology is
important for future development of therapies involving myocyte replacement
through either activation of resident stem cells or transplantation of stem
cells from an external source. Our data showing that loss of Foxp1
results in increased cell proliferation suggests that Foxp1 may
regulate an important step in this process. In light of these findings, it is
interesting to note that Foxp1 has been implicated as a tumor
suppressor gene (Banham et al.,
2001). Decreased expression of Foxp1 is observed in the
majority of colon and stomach tumors tested
(Banham et al., 2001
). Thus,
Foxp1 may regulate specific aspects of cell proliferation required
for normal organogenesis that, when disrupted, lead to defective development
or tumorigenesis.
Foxp1 and cardiomyocyte maturation
In conjunction with increased myocardial proliferation, cardiomyocyte
maturation in Foxp1/ hearts is disrupted, as
shown through expanded expression of Irx3, a transcription factor
normally expressed only in trabecular myocardium
(Christoffels et al., 2000) and
through the disorganized appearance of compact zone myocardium, where myocytes
lack their normal laminated organization. The disruption in Irx3
expression was specific, since expression of Anf, another gene
expressed exclusively in trabecular myocardium in early development
(Brand, 2003
), was unchanged.
However, appropriate myofiber assembly was apparent in Foxp1 null
embryo hearts when viewed by transmission electron microscopy (data not
shown). The reduced level of N-myc expression also supports the
hypothesis that compact zone development is disrupted in Foxp1 null
hearts. Although these defects could be secondary to other defects in outflow
tract or cushion development, Foxp1 is expressed in the myocardium in
a pattern that strongly suggests a direct effect on myocyte development. Taken
together, our data suggest that inactivation of Foxp1 locks myocytes
in a proliferative state where they do not mature properly, leading to
increased proliferation and defective maturation in mutant hearts.
Trabecular myocardium is considered to be more differentiated and mature
than compact zone myocardium, and this maturation is essential for proper
heart development (reviewed by Mikawa and
Fischman, 1996; Sedmera et
al., 2000
). Current models using retroviral tagging of primitive
cardiac myocytes suggest a single myocardial precusor that gives rise to both
compact and trabecular myocytes (Mikawa
and Fischman, 1996
; Ong et
al., 1998
). However, the molecular pathways controlling this
process are not well defined. Defects in the neuregulin signaling pathway
result in lack of cardiac trabecular formation, leading to early embryonic
death (Carraway, 1996
;
Gassmann et al., 1995
;
Kramer et al., 1996
;
Lee et al., 1995
;
Meyer and Birchmeier, 1995
).
Since neuregulin is expressed exclusively in the endocardium and the
ErbB receptors are expressed in the myocardium, these data indicate
an essential role for endocardialmyocardial signaling in trabecular
myocyte differentiation. Expression of neuregulin is normal in
Foxp1/ hearts (data not shown), suggesting
that Foxp1 may play an important role in regulating
endocardialmyocardial interactions in a pathway distinct from
neuregulin signaling.
The cardiovascular abnormalities observed in Foxp1 null embryos
are similar to those seen in multiple forms of congenital heart disease in
humans (Conway et al., 2003;
Dees and Baldwin, 2002
). Some
of these are caused by mutations in transcription factors such as Tbx1,
Foxc1 and GATA4. However, the genes causing many congenital
heart defects remain unknown. The data presented in this report suggest that
Foxp1 may be added to the growing list of candidate genes that cause
congenital heart disease in humans.
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ACKNOWLEDGMENTS |
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Footnotes |
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These laboratories contributed equally to this work
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Banham, A. H., Beasley, N., Campo, E., Fernandez, P. L., Fidler,
C., Gatter, K., Jones, M., Mason, D. Y., Prime, J. E., Trougouboff, P.
et al. (2001). The FOXP1 winged helix transcription factor is
a novel candidate tumor suppressor gene on chromosome 3p. Cancer
Res. 61,8820
-8829.
Bouchey, D., Argraves, W. S. and Little, C. D. (1996). Fibulin-1, vitronectin, and fibronectin expression during avian cardiac valve and septa development. Anat. Rec. 244,540 -551.[CrossRef][Medline]
Brand, T. (2003). Heart development: molecular insights into cardiac specification and early morphogenesis. Dev. Biol. 258,1 -19.[CrossRef][Medline]
Carraway, K. L., 3rd (1996). Involvement of the neuregulins and their receptors in cardiac and neural development. Bioessays 18,263 -266.[Medline]
Charron, J., Malynn, B. A., Fisher, P., Stewart, V., Jeannotte, L., Goff, S. P., Robertson, E. J. and Alt, F. W. (1992). Embryonic lethality in mice homozygous for a targeted disruption of the N-myc gene. Genes Dev. 6,2248 -2257.[Abstract]
Chen, Z., Friedrich, G. A. and Soriano, P. (1994). Transcriptional enhancer factor 1 disruption by a retroviral gene trap leads to heart defects and embryonic lethality in mice. Genes Dev. 8,2293 -2301.[Abstract]
Christoffels, V. M., Keijser, A. G., Houweling, A. C., Clout, D. E. and Moorman, A. F. (2000). Patterning the embryonic heart: identification of five mouse Iroquois homeobox genes in the developing heart. Dev. Biol. 224,263 -274.[CrossRef][Medline]
Conway, S. J., Kruzynska-Frejtag, A., Kneer, P. L., Machnicki, M. and Koushik, S. V. (2003). What cardiovascular defect does my prenatal mouse mutant have, and why? Genesis 35,1 -21.[CrossRef][Medline]
Costa, R. H., Kalinichenko, V. V. and Lim, L.
(2001). Transcription factors in mouse lung development and
function. Am. J. Physiol. Lung Cell Mol. Physiol.
280,L823
-838.
de la Pompa, J. L., Timmerman, L. A., Takimoto, H., Yoshida, H., Elia, A. J., Samper, E., Potter, J., Wakeham, A., Marengere, L., Langille, B. L. et al. (1998). Role of the NF-ATc transcription factor in morphogenesis of cardiac valves and septum. Nature 392,182 -186.[CrossRef][Medline]
Dees, E. and Baldwin, H. S. (2002). New frontiers in molecular pediatric cardiology. Curr. Opin. Pediatr. 14,627 -633.[CrossRef][Medline]
Ferland, R. J., Cherry, T. J., Preware, P. O., Morrisey, E. E. and Walsh, C. A. (2003). Characterization of Foxp2 and Foxp1 mRNA and protein in the developing and mature brain. J. Comp. Neurol. 460,266 -279.[CrossRef][Medline]
Gassmann, M., Casagranda, F., Orioli, D., Simon, H., Lai, C., Klein, R. and Lemke, G. (1995). Aberrant neural and cardiac development in mice lacking the ErbB4 neuregulin receptor. Nature 378,390 -394.[CrossRef][Medline]
Hiltgen, G. G., Markwald, R. R. and Litke, L. L. (1996). Morphogenetic alterations during endocardial cushion development in the trisomy 16 (Down syndrome) mouse. Pediatr. Cardiol. 17,21 -30.[CrossRef][Medline]
Kaestner, K. H., Knochel, W. and Martinez, D. E.
(2000). Unified nomenclature for the winged helix/forkhead
transcription factors. Genes Dev.
14,142
-146.
Keyes, W. M. and Sanders, E. J. (2002).
Regulation of apoptosis in the endocardial cushions of the developing chick
heart. Am. J. Physiol. Cell Physiol.
282,C1348
-1360.
Kramer, R., Bucay, N., Kane, D. J., Martin, L. E., Tarpley, J.
E. and Theill, L. E. (1996). Neuregulins with an
Ig-like domain are essential for mouse myocardial and neuronal development.
Proc. Natl. Acad. Sci. USA
93,4833
-4838.
Kume, T., Jiang, H., Topczewska, J. M. and Hogan, B. L.
(2001). The murine winged helix transcription factors, Foxc1 and
Foxc2, are both required for cardiovascular development and somitogenesis.
Genes Dev. 15,2470
-2482.
Kuo, C. T., Morrisey, E. E., Anandappa, R., Sigrist, K., Lu, M. M., Parmacek, M. S., Soudais, C. and Leiden, J. M. (1997). GATA4 transcription factor is required for ventral morphogenesis and heart tube formation. Genes Dev. 11,1048 -1060.[Abstract]
Lakkis, M. M. and Epstein, J. A. (1998).
Neurofibromin modulation of ras activity is required for normal
endocardial-mesenchymal transformation in the developing heart.
Development 125,4359
-4367.
Lee, K. F., Simon, H., Chen, H., Bates, B., Hung, M. C. and Hauser, C. (1995). Requirement for neuregulin receptor erbB2 in neural and cardiac development. Nature 378,394 -398.[CrossRef][Medline]
Lu, M. M., Li, S., Yang, H. and Morrisey, E. E. (2002). Foxp4: a novel member of the Foxp subfamily of winged-helix genes co-expressed with Foxp1 and Foxp2 in pulmonary and gut tissues. Mech Dev. 119 (Suppl. 1), S197-202.[CrossRef][Medline]
Maschhoff, K. L., Anziano, P. Q., Ward, P. and Baldwin, H. S. (2003). Conservation of Sox4 gene structure and expression during chicken embryogenesis. Gene 320, 23-30.[CrossRef][Medline]
Meyer, D. and Birchmeier, C. (1995). Multiple essential functions of neuregulin in development. Nature 378,386 -390.[CrossRef][Medline]
Mikawa, T. and Fischman, D. A. (1996). The polyclonal origin of myocyte lineages. Annu. Rev. Physiol. 58,509 -521.[CrossRef][Medline]
Moens, C. B., Stanton, B. R., Parada, L. F. and Rossant, J.
(1993). Defects in heart and lung development in compound
heterozygotes for two different targeted mutations at the N-myc locus.
Development 119,485
-499.
Moorman, A. F. and Christoffels, V. M. (2003).
Cardiac chamber formation: development, genes, and evolution.
Physiol. Rev. 83,1223
-1267.
Ong, L. L., Kim, N., Mima, T., Cohen-Gould, L. and Mikawa, T. (1998). Trabecular myocytes of the embryonic heart require N-cadherin for migratory unit identity. Dev. Biol. 193, 1-9.[CrossRef][Medline]
Ranger, A. M., Grusby, M. J., Hodge, M. R., Gravallese, E. M., de la Brousse, F. C., Hoey, T., Mickanin, C., Baldwin, H. S. and Glimcher, L. H. (1998). The transcription factor NF-ATc is essential for cardiac valve formation. Nature 392,186 -190.[CrossRef][Medline]
Sawai, S., Shimono, A., Wakamatsu, Y., Palmes, C., Hanaoka, K.
and Kondoh, H. (1993). Defects of embryonic
organogenesis resulting from targeted disruption of the N-myc gene in the
mouse. Development 117,1445
-1455.
Schilham, M. W., Oosterwegel, M. A., Moerer, P., Ya, J., de Boer, P. A., van de Wetering, M., Verbeek, S., Lamers, W. H., Kruisbeek, A. M., Cumano, A. et al. (1996). Defects in cardiac outflow tract formation and pro-B-lymphocyte expansion in mice lacking Sox-4. Nature 380,711 -714.[CrossRef][Medline]
Sedmera, D., Pexieder, T., Vuillemin, M., Thompson, R. P. and Anderson, R. H. (2000). Developmental patterning of the myocardium. Anat. Rec. 258,319 -337.[CrossRef][Medline]
Shu, W., Yang, H., Zhang, L., Lu, M. M. and Morrisey, E. E.
(2001). Characterization of a new subfamily of
winged-helix/forkhead (Fox) genes that are expressed in the lung and act as
transcriptional repressors. J. Biol. Chem.
276,27488
-27497.
Svensson, E. C., Huggins, G. S., Lin, H., Clendenin, C., Jiang, F., Tufts, R., Dardik, F. B. and Leiden, J. M. (2000). A syndrome of tricuspid atresia in mice with a targeted mutation of the gene encoding Fog-2. Nat. Genet. 25,353 -356.[CrossRef][Medline]
Swiderski, R. E., Reiter, R. S., Nishimura, D. Y., Alward, W. L., Kalenak, J. W., Searby, C. S., Stone, E. M., Sheffield, V. C. and Lin, J. J. (1999). Expression of the Mf1 gene in developing mouse hearts: implication in the development of human congenital heart defects. Dev. Dyn. 216,16 -27.[CrossRef][Medline]
Tevosian, S. G., Deconinck, A. E., Tanaka, M., Schinke, M., Litovsky, S. H., Izumo, S., Fujiwara, Y. and Orkin, S. H. (2000). FOG-2, a cofactor for GATA transcription factors, is essential for heart morphogenesis and development of coronary vessels from epicardium. Cell 101,729 -739.[Medline]
Tybulewicz, V. L., Crawford, C. E., Jackson, P. K., Bronson, R. T. and Mulligan, R. C. (1991). Neonatal lethality and lymphopenia in mice with a homozygous disruption of the c-abl proto-oncogene. Cell 65,1153 -1163.[Medline]
Wang, B., Lin, D., Li, C. and Tucker, P.
(2003). Multiple domains define the expression and regulatory
properties of Foxp1 forkhead transcriptional repressors. J. Biol.
Chem. 278,24259
-24268.
Winnier, G. E., Kume, T., Deng, K., Rogers, R., Bundy, J., Raines, C., Walter, M. A., Hogan, B. L. and Conway, S. J. (1999). Roles for the winged helix transcription factors MF1 and MFH1 in cardiovascular development revealed by nonallelic noncomplementation of null alleles. Dev. Biol. 213,418 -431.[CrossRef][Medline]
Ya, J., Schilham, M. W., de Boer, P. A., Moorman, A. F.,
Clevers, H. and Lamers, W. H. (1998). Sox4-deficiency
syndrome in mice is an animal model for common trunk. Circ.
Res. 83,986
-994.
Yamagishi, H., Maeda, J., Hu, T., McAnally, J., Conway, S. J.,
Kume, T., Meyers, E. N., Yamagishi, C. and Srivastava, D.
(2003). Tbx1 is regulated by tissue-specific forkhead proteins
through a common Sonic hedgehog-responsive enhancer. Genes
Dev. 17,269
-281.