TBX5 and cardiac proliferation

描述（由申请人提供）：识别和表征参与心脏细胞增殖早期步骤的分子途径对于理解先天性心脏病的病理和治疗至关重要。然而，迄今为止，控制胚胎心脏细胞周期进展的早期分子途径在很大程度上仍然未知。为了解决这些问题，我们克隆并鉴定了在人类先天性心脏病Holt Oram综合征（HOS）中突变的非洲爪蟾T-box基因Tbx5。我们已经证明TBX5在体内对于心脏细胞周期的G1/ s转变是必要的和充分的。从这些和其他研究中，我们假设TBX5的功能是维持心脏祖细胞群的增殖。非洲爪蟾提供了一个无与伦比的机会来解决这一假设，因为可以获得无限的胚胎心脏组织，心脏外植体测定的发展，egfp转基因报告青蛙的可用性，标记基因表达域和标记活心脏组织中细胞周期的特定阶段，以及我们最近描述的一组广泛的抗体，标记发育中的非洲爪蟾心脏中的细胞周期成分。在这里，我们建议以TBX5为起点来阐明控制心脏祖细胞增殖的分子网络。这将通过确定TBX5是否直接调节胚胎心脏中的cyclin D1和cyclin E2，表征SIN3B-TBX5蛋白-蛋白相互作用在心脏细胞周期调节中的生物学意义，以及通过TBX5调节心脏细胞周期G1到S转变的内源性心脏有丝分裂原来实现。

DESCRIPTION (provided by applicant): The identification and characterization of the molecular pathways involved in the early steps of cardiac cell proliferation are absolutely critical to understanding the pathologies and treatment of congenital heart disease. However, to date the early molecular pathways that control the progression of the embryonic cardiac cell cycle remain largely unknown. To address these issues, we cloned and characterized the Xenopus T-box gene Tbx5, the gene mutated in the human congenital heart disease Holt Oram syndrome (HOS). We have shown that TBX5 is both necessary and sufficient in vivo for the cardiac G1/S-transition of the cell cycle. From these and other studies, we hypothesize that TBX5 functions to maintain proliferation of cardiac progenitor populations. Xenopus offers an unparalleled opportunity to address this hypothesis due to the access of unlimited embryonic cardiac tissue, the development of cardiac explant assays, the availability EGFP-transgene reporter frogs that mark gene expression domains and mark specific phases of the cell cycle in living cardiac tissues, and our recent description of an extensive panel of antibodies that mark cell cycle components in the developing Xenopus heart. Here we propose to use TBX5 as a starting point to elucidate the molecular networks which control the proliferation of cardiac progenitor cells. This will be accomplished by determining if TBX5 directly regulates cyclin D1 and cyclin E2 in the embryonic heart, characterizing the biological significance of the SIN3B-TBX5 protein-protein interaction in cardiac cell cycle regulation, and through the identification of the endogenous cardiac mitogens which function through TBX5 to regulate the G1 to S transition of the cardiac cell cycle. PUBLIC HEALTH RELEVANCE The ability to isolate and propagate cell populations that can differentiate into cardiomyocytes in vivo offers the opportunity to treat a wide range of cardiac diseases. This proposal focuses on the characterization of the transcription factor TBX5, the gene mutated in the congenital heart disease Holt Oram syndrome, and its endogenous role in cardiac proliferation. Our immediate goal is to define and characterize the molecular pathways by which TBX5 functions with the overall goal, to use TBX5 as a starting point in an effort to begin to elucidate the pathways and molecular networks which control the survival and proliferation of cardiomyocyte progenitor cells.