Congenital heart defects are among the most prevalent and serious diseases affecting humans. Thus, the detrimental impact on the affected individuals, families, and society emphasizes the need for a better understanding of the underlying molecular events at the organ and cell levels. The cardiovascular system is in particular affected by altered T-box gene function. The vertebrate genome contains a family of at least 18 different T-box (Tbx) genes. Among those, Tbx5 has functions in a variety of cardiac lineages and structures, and mutations in human TBX5 result in Holt-Oram syndrome (HOS), a disease characterized by congenital heart and limb defects. The cardiac manifestations in this heart/limb disease range from atrial and ventricular septal defects to complex malformations such as tetralogy of Fallot. The HOS phenotypes can result form either reduced or increased amounts of Tbx5, indicating that the levels of Tbx proteins are critical for normal functioning. In spite of their importance in embryogenesis and disease, the mechanisms by which the encoded transcription factors exert their functions are not yet understood. The long-term objective of this project is to elucidate how the Tbx5 transcription factor interacts within a molecular regulatory network during cardiogenesis, and how and why these processes sometimes fail. We have identified a novel Tbx5 binding protein, Lmp4. We propose testing the hypothesis that Lmp4 regulates Tbx5 transcription factor activity by controlling its subcellular localization. The focus of this study is to investigate the role of Tbx5/Lmp4 protein complex formation on Tbx5 nuclear localization, changes in Tbx5-dependent cardiac gene expression, heart patterning, and morphogenesis. At the cellular level we will determine the localization of Tbx5 transcription factors and their binding partner and ask whether manipulation of protein levels and subcellular localization interferes with downstream gene expression. At the organism level we will use complementary strategies in zebrafish and chicken embryo models. Gain- and loss-of-function experiments in zebrafish will test the role of Lmp4 in early fish embryogenesis with a special emphasis on heart formation. Forced misexpression of wild type and mutated forms of the binding factor in chicken hearts will investigate its role on cardiac-specific gene expression and pattern formation. Ultimately, these studies will provide a broader perspective of Tbx function, necessary for a better understanding of congenital cardiovascular malformations associated with Tbx5 gene mutations, and will provide insight into a previously unknown mechanism for transcription factor regulation in cardiogenesis. ? ? ?

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL085834-02
Application #
7227729
Study Section
Cardiovascular Differentiation and Development Study Section (CDD)
Program Officer
Schramm, Charlene A
Project Start
2006-07-01
Project End
2010-05-31
Budget Start
2007-06-01
Budget End
2008-05-31
Support Year
2
Fiscal Year
2007
Total Cost
$364,089
Indirect Cost
Name
Children's Memorial Hospital (Chicago)
Department
Type
DUNS #
074438755
City
Chicago
State
IL
Country
United States
Zip Code
60611
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Camarata, Troy; Snyder, Diana; Schwend, Tyler et al. (2010) Pdlim7 is required for maintenance of the mesenchymal/epidermal Fgf signaling feedback loop during zebrafish pectoral fin development. BMC Dev Biol 10:104
Camarata, Troy; Krcmery, Jennifer; Snyder, Diana et al. (2010) Pdlim7 (LMP4) regulation of Tbx5 specifies zebrafish heart atrio-ventricular boundary and valve formation. Dev Biol 337:233-45
Kulisz, Andre; Simon, Hans-Georg (2008) An evolutionarily conserved nuclear export signal facilitates cytoplasmic localization of the Tbx5 transcription factor. Mol Cell Biol 28:1553-64
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Camarata, Troy; Bimber, Benjamin; Kulisz, Andre et al. (2006) LMP4 regulates Tbx5 protein subcellular localization and activity. J Cell Biol 174:339-48