The role of Lmp4 in the regulation of the cardiac transcription factor Tbx5

描述（由申请人提供）：先天性心脏缺陷是影响人类最普遍和最严重的疾病之一。因此，对受影响的个人，家庭和社会的有害影响强调需要更好地了解器官和细胞水平的潜在分子事件。心血管系统尤其受T-box基因功能改变的影响。脊椎动物基因组包含至少18个不同的T-box （Tbx）基因家族。其中，Tbx5在多种心脏谱系和结构中具有功能，人类Tbx5的突变导致Holt-Oram综合征（HOS），这是一种以先天性心脏和肢体缺陷为特征的疾病。这种心脏/肢体疾病的心脏表现范围从心房和室间隔缺损到复杂的畸形，如法洛四联症。HOS表型可以由Tbx5的减少或增加引起，这表明Tbx蛋白的水平对正常功能至关重要。尽管编码转录因子在胚胎发生和疾病中具有重要作用，但其发挥功能的机制尚不清楚。该项目的长期目标是阐明Tbx5转录因子在心脏发生过程中如何在分子调控网络中相互作用，以及这些过程有时如何以及为什么失败。我们已经鉴定出一种新的Tbx5结合蛋白Lmp4。我们提出验证Lmp4通过控制其亚细胞定位来调节Tbx5转录因子活性的假设。本研究的重点是探讨Tbx5/Lmp4蛋白复合物形成在Tbx5核定位、Tbx5依赖性心脏基因表达变化、心脏模式和形态发生中的作用。在细胞水平上，我们将确定Tbx5转录因子及其结合伙伴的定位，并询问蛋白质水平和亚细胞定位的操纵是否会干扰下游基因的表达。在有机体水平上，我们将在斑马鱼和鸡胚胎模型中使用互补策略。斑马鱼的功能获得和功能丧失实验将测试Lmp4在早期鱼类胚胎发生中的作用，特别强调心脏形成。在鸡心脏中强行错表达野生型和突变形式的结合因子将研究其在心脏特异性基因表达和模式形成中的作用。最终，这些研究将为Tbx功能提供更广阔的视角，这对于更好地理解与Tbx5基因突变相关的先天性心血管畸形是必要的，并将为转录因子在心脏发生中的调节机制提供以前未知的见解。

DESCRIPTION (provided by applicant): 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.