title: Differential regulation of Tbx5 protein expression and sub-cellular localization during heart development.
abstract: The T-box transcription factor Tbx5 can interact with Nkx2.5 and Gata4 transcription factors to synergistically regulate heart-specific genes in the nucleus. While a nuclear role for Tbx5 is clearly defined, we have previously shown that Tbx5 shuttles from nuclear to cytoplasmic sites, forming a complex with the PDZ-LIM protein LMP4 on the actin cytoskeleton. In this study, using a developmental series of chicken hearts, we provide the first evidence for differential Tbx5 protein expression and sub-cellular localization during cardiogenesis. At the tissue level, we show temporally and spatially restricted Tbx5 co-expression with LMP4. In cells co-expressing LMP4 and Tbx5 we demonstrate dynamic Tbx5 re-localization from exclusively nuclear to nuclear and cytoplasmic expression in the atrio-ventricular cushion. Furthermore, in coronary vessel development we show exclusive cytoplasmic localization of Tbx5, indicating a function for Tbx5 in the cytoplasm. In addition, we discover unknown regulation of Tbx5 and LMP4 expression in epicardial tissue, suggesting a specific role for Tbx5 in epicardial formation. These studies provide in vivo significance of the LMP4/Tbx5 protein interaction, suggesting both nuclear and cytoplasmic roles for Tbx5. The shuttling between nuclear and cytoplasmic sites reveals a novel mechanism for Tbx transcription factor regulation in chicken heart development allowing new insights for a better understanding of the molecular basis of hand/heart birth defects associated with TBX5 mutations.
authors.affiliation: Department of Pediatrics, Northwestern University, The Feinberg School of Medicine, Children's Memorial Research Center, Chicago, IL 60614, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Bimber
authors.forename: Robert W
authors.initials: RW
authors.lastname: Dettman
authors.forename: Hans-Georg
authors.initials: HG
authors.lastname: Simon
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002642:Chick Embryo; D003331:Coronary Vessels / Q000196:embryology; D018507:Gene Expression Regulation, Developmental; D006321:Heart / Q000196:embryology*; D009206:Myocardium / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D010496:Pericardium / Q000196:embryology; D011485:Protein Binding; D021381:Protein Transport; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D020825:T-Box Domain Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism
chemical_list: D011506:Proteins; D020825:T-Box Domain Proteins; C103172:T-box transcription factor 5