HOMEOBOX GENE PITX2 EXPRESSION IN STEM CELLS

造血干细胞只占骨髓单核细胞的很小一部分，这些细胞具有自我更新的能力，并能在控制下分化为外周血的所有细胞成分。赋予干细胞表型的分子信号和控制干细胞增殖和分化的机制尚不完全清楚。在初步工作中，我们已经确定了一个分化的同源盒基因（Pitx2），它在小鼠造血干细胞/祖细胞中表达，但在分化细胞中不表达。我们的研究已经证明了该基因在造血干细胞/祖细胞和胚胎干细胞中的一种新的mRNA亚型的表达。本提案的研究目标是确定该基因在造血中的作用。具体来说，我们建议：表征该基因（产物）在体外和体内对造血祖细胞生长和分化的时间和过度表达；研究该基因功能丧失对携带该基因靶向破坏的ES细胞以及表达Pitx2显性阴性版本的各种造血细胞的影响；并对Pitx2的下游基因靶点及调控Pitx2表达的元件进行了表征。

Hematopoietic stem cells comprise a very small fraction of bone marrow mononuclear cells, which retain the capacity for self-renewal as well as controlled differentiation into all the cellular elements of the peripheral blood. The molecular signals that confer the stem cell phenotype and the mechanisms that control stem cell proliferation and differentiation are incompletely understood. In preliminary work, we have identify a divergent homeobox gene (Pitx2) that is expressed in murine hematopoietic stem/progenitor cells but not in differentiated cells. Our studies have demonstrated the expression of a novel mRNA isoforms of this gene in hematopoietic stem/progenitor cells and embryonic stem cells. The research goals of this proposal are to establish the role of this gene in hematopoiesis. Specifically, we propose to: characterize the temporal and over-expression of the gene (products) on hematopoietic progenitor cell growth and differentiation in vitro as well as in vivo: study the effects of loss of function of the gene in ES cells carrying targeted disruptions of the gene as well as in various hematopoietic cells expressing a dominant negative version of Pitx2; and characterize the downstream gene targets of Pitx2 as well as the elements that regulate the expression of Pitx2.