c-myb in B Cell Development and Function

描述(申请人提供)：很明显，原癌基因c-myb在造血过程中起着至关重要的作用。在每个造血系中，c-myb在分化的未成熟阶段大量表达，在分化过程中相对较晚的时候被关闭。然而，对于c-myb在造血成熟过程中所扮演的角色，该作用是如何被介导的，以及调节c-myb表达的信号通路是什么，几乎一无所知。C-myb基因纯合子缺失的小鼠在胚胎发育的第15天死于严重的贫血。这一发现以图形方式证明了c-myb在造血过程中的重要性，但排除了对c-myb在分化后期的活性的研究。缺乏一个易于处理的遗传系统，允许c-myb在造血成熟的后期发生突变，这一直是理解c-myb在造血中的作用的主要障碍。在B细胞在骨髓中的发育过程中，c-myb在前B细胞和前B细胞中表达，但在未成熟的、循环的B细胞和外周B细胞中的表达水平大约低20倍。为了开始了解c-myb在B细胞发育中所起的作用，我们培育了携带c-myb等位基因的小鼠，该等位基因被Cre重组酶删除。通过将这些小鼠培育成可将Cre表达定向到骨髓中B细胞发育的早期阶段或以可诱导的方式表达的可用的小鼠品系，我们将确定c-myb在B细胞发育和外周B细胞亚群维持中所起的作用。此外，这些小鼠将对该领域至关重要，并将使人们开始深入了解c-myb在造血过程中的功能，以及在c-myb功能仍然知之甚少的其他系统中。该方案的目标是：1)确定c-myb表达在哪个阶段对B细胞的发育和功能至关重要；2)确定c-myb表达不当对B细胞发育和功能的影响；3)确定c-myb的功能结构域，以驱动B细胞在骨髓中的发育。

DESCRIPTION (provided by applicant): It is clear that the c-myb protooncogene plays a crucial role during hematopoiesis. In each hematopoietic lineage, c-myb is abundantly expressed at the immature stages of differentiation and is turned off at a relatively late time during the differentiation process. However, virtually nothing is known about what role c-myb plays during hematopoietic maturation, how that role is mediated or what the signaling pathways are that regulate c-myb expression. Mice that are homozygous null at the c-myb locus die at day fifteen during embryo genesis from a severe anemia. This finding graphically demonstrated the significance of c-myb during hematopoiesis but has precluded study of c-myb activity at the later stages of differentiation. The lack of a tractable genetic system that will allow mutation of c-myb during the later stages of hematopoietic maturation has been a major impediment to understanding the role of c-myb during hematopoiesis. During B cell development in the bone marrow, c-myb is expressed in pre-B and pre-B cells but is expressed at levels approximately 20-fold lower in immature, recirculating B cells and peripheral B cells. To begin to understand the role played by c-myb during B cell development we have produced mice that carry a c-myb allele targeted with IoxP sites for deletion by the Cre recombinase. By breeding these mice to available mouse strains that direct Cre expression either to the early stages of B cell development in the bone marrow or in an inducible fashion, we will define the role played by c-myb during B cell development and the maintenance of peripheral B cell subsets. In addition, these mice will be crucial to the field and will allow one to begin to gain insight into c-myb function during hematopoiesis as well as in other systems where c-myb function remains poorly understood. The goals of this proposal are: 1) to determine at what stage c-myb expression is essential for B cell development and function, 2) to determine the consequences of inappropriate c-myb expression to B cell development and function and 3) to identify c-myb functional domains required to drive B cell development in the bone marrow.