Molecular Events Initiating B Cell Fate Determination

描述（由申请人提供）：B淋巴细胞是重要的血细胞，其产生或功能的改变可引起重大疾病。我们感兴趣的是了解血液干细胞如何启动B细胞的发育。描述正常的B细胞发育途径将为许多血液病的分子和细胞基础提供见解。尽管在理解从承诺B细胞前体生成幼稚B细胞方面取得了相当大的进展，但对这一过程如何开始知之甚少。该项目将探索酪氨酸激酶Flt3受体、HoxA蛋白和B细胞命运决定因子EBF之间意想不到的调控联系。我们的新数据表明，这种调节连接在调节干细胞向Pro-B的转变中起着重要作用，因此，B淋巴细胞的数量产生。具体来说，我们将了解Flt3信号如何启动一系列事件，逐渐使骨髓中的多电位祖细胞偏向于B谱系。令人兴奋的新数据显示，Flt3信号以配体剂量依赖的方式调节原代B细胞命运决定因子E2A的活性，E2A是EBF基因的关键调节因子。EBF一旦表达，就会协调B细胞的分化。EBF-/-细胞系的基因表达谱指出EBF在B细胞发育过程中的新作用，即控制发育调节的HoxA蛋白簇的表达。阐明控制HoxA表达的调控回路是重要的，因为失调的表达会损害B细胞分化。首先，我们将确定Flt3信号传导和EBF表达之间的分子事件。然后我们将确定EBF、HoxA和Flt3之间控制B淋巴细胞产生的调节联系。总的来说，这些实验将提供一个重要过程的基本知识，即白细胞的产生，白细胞产生抗体来对抗感染。这些信息应该有助于确定干预血细胞癌和免疫缺陷疾病的分子靶点。公共卫生相关性：在血细胞发育过程中，干细胞向Pro-B过渡是控制B细胞稳态的关键检查点。该项目的重点是确定三个关键因素，受体酪氨酸激酶Flt3、HoxA蛋白和B细胞命运决定因子EBF，通过这三个关键因素协调这一关键检查点的分子电路。

DESCRIPTION (provided by applicant): B lymphocytes are critical blood cells and altered production or function can cause significant disease. We are interested in understanding how blood stem cells initiate B cell development. Delineating the normal B cell developmental pathway will provide insight into the molecular and cellular basis of many hematologic diseases. Although considerable progress has been made in understanding the generation of naive B cells from committed B cell precursors, little is known about how this process begins. This project will exploit exciting new findings concerning an unexpected regulatory connection between the receptor tyrosine kinase Flt3, HoxA proteins, and the B cell fate determinant EBF. Our new data suggest that this regulatory connection plays an important role in regulating the stem cell to Pro-B transition, and hence, the numbers of B lymphocytes generated. Specifically, we will learn how Flt3 signaling initiates a series of events, gradually biasing multipotential progenitors in bone marrow into the B lineage. Exciting new data revealed that Flt3 signaling, in a ligand-dose dependent fashion, regulates the activity of the primary B cell fate determinant, E2A, a key regulator of the EBF gene. Once expressed, EBF orchestrates B cell differentiation. Gene expression profiling of an EBF-/- cell line pointed to novel role for EBF during B cell development, namely controlling expression of a developmentally regulated cluster of HoxA proteins. Elucidating regulatory circuits that control HoxA expression is important, as dysregulated expression impairs B cell differentiation. First we will determine the molecular events between Flt3 signaling and EBF expression. Then we will determine the regulatory connection between EBF, HoxA, and Flt3 that controls the production of B lymphocytes. Overall, these experiments will provide basic knowledge of a vital process, the production of white blood cells that make antibodies to fight infections. The information should help identify molecular targets for intervention in blood cell cancers and immunodeficiency diseases. PUBLIC HEALTH RELEVANCE: During blood cell development, the stem cell to Pro-B transition is a pivotal checkpoint that controls B cell homeostasis. This project focuses on determining the molecular circuitry through which three critical factors, the receptor tyrosine kinase Flt3, HoxA proteins, and the B cell fate determinant EBF, orchestrate this critical checkpoint.