Murine T-box transcription factor Tbx20 acts as a repressor during heart development, and is essential for adult heart integrity, function and adaptation
Fiona A. Stennard
2
Mauro W. Costa
1
2
Donna Lai
2
Christine Biben
2
Milena B. Furtado
2
Mark J. Solloway
2
David J. McCulley
0
Christiana Leimena
2
Jost I. Preis
2
Sally L. Dunwoodie
2
3
David E. Elliott
2
4
Owen W. J. Prall
2
Brian L. Black
0
Diane Fatkin
2
3
Richard P. Harvey
)
2
3
0
Cardiovascular Research Institute, University of California
,
San Francisco, CA 94143-0130
,
USA
1
Laboratorio de Cardiologia Celular e Molecular, Instituto de Biofisica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro
,
20941-000
,
Brazil
2
Victor Chang Cardiac Research Institute, St Vincent's Hospital
,
384 Victoria Street, Darlinghurst 2010, New South Wales
,
Australia
3
Faculties of Medicine and Life Sciences, University of New South Wales
,
Kensington 2056, New South Wales
,
Australia
4
Present address: The Wellcome Trust/Cancer Research UK, Gurdon Institute of Cancer and Developmental Biology, University of Cambridge
,
Tennis Court Road, Cambridge CB2 1QR
,
UK
heart development, and is essential for adult heart integrity,
-
t The genetic hierarchies guiding lineage specification and
n morphogenesis of the mammalian embryonic heart are
em poorly understood. We now show by gene targeting that
p murine T-box transcription factor Tbx20 plays a central
o
le role in these pathways, and has important activities in both
ev cardiac development and adult function. Loss of Tbx20
D results in death of embryos at mid-gestation with
grossly abnormal heart morphogenesis. Underlying these
disturbances was a severely compromised cardiac
transcriptional program, defects in the molecular
prepattern, reduced expansion of cardiac progenitors and a
block to chamber differentiation. Notably, Tbx20-null
embryos showed ectopic activation of Tbx2 across the whole
heart myogenic field. Tbx2 encodes a transcriptional
repressor normally expressed in non-chamber
myocardium, and in the atrioventricular canal it has been
proposed to inhibit chamber-specific gene expression
Cardiac development in mammals is guided by an ancient and
conserved genetic program (Cripps and Olson, 2002; Harvey,
2002; Zaffran and Frasch, 2002). However, how the cardiac
program unfolds, the specific relationships between patterning
events and the transcription factor hierarchy, and how
cardiomyocyte function impacts on heart form remain poorly
understood.
Of 18 T-box factor genes identified in mammals, at least six
of them (Tbx1/2/3/5/18/20) are expressed in the developing
heart (Plageman and Yutzey, 2004). T-box proteins are
characterized by the presence of a sequence-specific
DNAbinding domain called the T-box (Smith, 1999). During
embryogenesis, T-box genes are expressed in restricted and
sometimes overlapping domains throughout gastrulation
and/or organogenesis, and in some cases roles in controlling
through competition with positive factor Tbx5. Our data
demonstrate a repressive activity for Tbx20 and place it
upstream of Tbx2 in the cardiac genetic program. Thus,
hierarchical, repressive interactions between Tbx20 and
other T-box genes and factors underlie the primary lineage
split into chamber and non-chamber myocardium in the
forming heart, an early event upon which all subsequent
morphogenesis depends. Additional roles for Tbx20
in adult heart integrity and contractile function were
revealed by in-vivo cardiac functional analysis of Tbx20
heterozygous mutant mice. These data suggest that
mutations in human cardiac transcription factor genes,
possibly including TBX20, underlie both congenital heart
disease and adult cardiomyopathies.
cell fate and migration have been demonstrated (Chapman and
Papaioannou, 1998; Naiche and Papaioannou, 2003; Russ et
al., 2000). T-box factors can act up- or downstream of signaling
factors of the TGF- (Suzuki et al., 2004), fibroblast growth
factor (Brown et al., 2004; Hu et al., 2004; Sakiyama et al.,
2003; Yamagishi et al., 2003), sonic hedgehog (Suzuki et al.,
2004; Yamagishi et al., 2003) and wingless-related (Takeuchi
et al., 2003) superfamilies.
Haploinsufficiencies for several human T-box genes have
been linked to congenital anomaly syndromes (Bongers et al.,
2004; Packham and Brook, 2003). Two of these involve
cardiac malformations. Di George syndrome, also occurring
as part of chromosome 22q11 deletion syndrome, is
characterized by dysmorphogenesis of the cardiac outflow
tract (OFT), as well as thymic, splenic and craniofacial
abnormalities (Yamagishi and Srivastava, 2003). Holt Oram
syndrome is characterized by congenital abnormalities of
the upper limbs and heart, the latter involving atrial
and ventricular septal defects, tetralogy of Fallot and
atrioventricular conduction block (Gruber and Epstein,
2004). Targeted mutation of causative genes in mice has
reproduced many aspects of the human cardiac disease
phenotypes, thus providing valuable models for
understanding underlying mechanisms (Bruneau et al., 2001;
Lindsay et al., 2001; Merscher et al., 2001; Yamagishi and
Srivastava, 2003).
Tbx20 is an ancient m (...truncated)