Conditional Mutagenesis to Study c-Myb Function

描述(申请人提供)：很明显，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起的作用、该作用是如何被介导的、或者是什么信号通路调节c-Myb的表达，人们几乎一无所知。Myb基因座纯合子缺失的小鼠在胚胎发育过程中因严重贫血而在第15天死亡。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。在胸腺T细胞发育过程中，CD_4和CD_8双阴性(DM)和双阳性(DP)胸腺细胞含有丰富的c-Myb，而CD_4~+和CD_8~+单阳性(SP)细胞仅含有10~20%的c-Myb。在外周，c-Myb在静止期T细胞中低水平表达，但在细胞周期的G1晚期/SD早期的增殖T细胞中表达增加。为了开始了解c-Myb在T细胞发育中所起的作用，我们培育了携带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表达定向到胸腺T细胞发育的不同阶段的可用的小鼠品系，我们已经确定了T细胞发育过程中需要c-Myb的临界点：从发育的DN阶段过渡到DP阶段，对于预先选择的DP细胞的生存和CD4 SP胸腺细胞的分化。最近，我们确定了c-Myb在维持T细胞内稳态和调节T细胞辅助功能中的作用。本研究的目的是了解c-Myb在T细胞发育的糖尿病肾病阶段、外周T细胞动态平衡和辅助T细胞功能中的作用基础。

DESCRIPTION (provided by applicant): It is clear that the 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 signaling pathways regulate c- Myb expression. Mice that are homozygous null at the Myb locus die at day fifteen during embryogenesis 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 Myb during the later stages of hematopoietic maturation has been a major impediment to understanding the role of c-Myb during hematopoiesis. During T cell development in the thymus, CD4 and CD8 double negative (DM) and double positive (DP) thymocytes contain abundant amounts of c-Myb while CD4+ and CD8+ single positive (SP) cells contain only 10 to 20% as much c-Myb. In the periphery, c-Myb is expressed at only low levels in resting T cells, but expression increases in proliferating T cells in late G1/early SD phase of the cell cycle. To begin to understand the role played by c- Myb during T cell development we have produced mice that carry a Myb allele targeted with loxP sites for deletion by the Cre recombinase. By breeding these mice to available mouse strains that direct Cre expression to different stages of T cell development in the thymus we have defined critical points during T cell development where c-Myb is required: transition from the DN to the DP stage of development, for the survival of pre-selection DP cells and the differentiation of CD4 SP thymocytes. More recently we have identified roles for c-Myb in maintaining T cell homeostasis and mediating T cell helper function. The goals of this proposal are to understand the basis for c-Myb function during the DN stage of T cell development, in peripheral T homeostasis and helper T cell function.