c-myb in B Cell Development and Function

描述（由申请人提供）：很明显，c-myb原癌基因在造血过程中起着至关重要的作用。在每个造血谱系中，c-myb在分化的未成熟阶段大量表达，并在分化过程中相对较晚的时间关闭。然而，对于c-myb在造血成熟过程中所起的作用，该作用是如何介导的，以及调节c-myb表达的信号通路是什么，几乎一无所知。在c-myb位点纯合子为零的小鼠在胚胎发生的第15天死于严重贫血。这一发现图解地证明了c-myb在造血过程中的重要性，但排除了对分化后期c-myb活性的研究。在造血成熟的后期阶段，缺乏一个可控制的遗传系统允许c-myb突变，这是理解c-myb在造血过程中的作用的主要障碍。在骨髓B细胞发育过程中，c-myb在前B细胞和前B细胞中表达，但在未成熟、再循环的B细胞和外周B细胞中的表达水平约低20倍。为了开始了解c-myb在B细胞发育过程中所起的作用，我们制造了携带c-myb等位基因的小鼠，该等位基因被Cre重组酶靶向IoxP位点进行删除。通过将这些小鼠培育成可获得的小鼠品系，将Cre表达引导到骨髓中B细胞发育的早期阶段或以诱导的方式，我们将确定c-myb在B细胞发育和维持外周B细胞亚群中所起的作用。此外，这些小鼠将对该领域至关重要，并将允许人们开始深入了解造血过程中的c-myb功能，以及c-myb功能仍然知之甚少的其他系统。本提案的目标是：1)确定c-myb在哪个阶段对B细胞的发育和功能至关重要，2)确定不适当的c-myb表达对B细胞发育和功能的影响，3)确定驱动骨髓中B细胞发育所需的c-myb功能域。

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.