Zfx, A Novel Transcriptional Regulator of Hematopoiesis

描述(申请人提供)：哺乳动物的造血基于造血干细胞(HSC)的活动，在整个成年生活中经历不断的自我更新。骨髓HSC的长期维持似乎受到高度特异的转录机制的调控，这些机制在很大程度上仍不清楚。自我更新的HSC的后代启动了有序的分化程序，产生了所有的血统。特别是，B和T淋巴细胞的发育涉及未成熟前体细胞的大规模增殖扩张。HSC的自我更新和淋巴细胞扩张似乎对细胞周期抑制物p16lnk4a水平的升高非常敏感，p16lnk4a被定义不明确的分子通路积极抑制。我们对造血的研究主要集中在Zfx上，这是一种进化上保守的含锌指转录因子。在初步实验中，小鼠Zfx在造血系统中的失活会导致成人骨髓HSC群体的特异性丧失。此外，未成熟的B和T淋巴细胞的扩增严重受损。初步的表达分析表明，这些表型可能是由于在没有Zfx的情况下p16lnk4a的过度表达所致。因此，Zfx可能是HSC自我更新和p16lnk4a上游未成熟淋巴细胞扩增的重要且特异的正性调节因子。为了验证这一假设，本文提出了三个具体目标。首先，Zfx在HSC自我更新中的作用将在职能层面上得到表征。其次，将研究Zfx缺陷淋巴细胞的早期发育和生长。第三，通过对Zfx在造血细胞中靶基因的鉴定和功能分析，建立Zfx活性的分子基础。这些研究可能确定有助于维持HSC和未成熟淋巴细胞的新的分子机制，可能是通过抑制p16lnk4a。

DESCRIPTION (provided by applicant): Mammalian hematopoiesis is based on the activity of hematopoietic stem cells (HSC) that undergo continuous self-renewal throughout the adult life. The long-term maintenance of bone marrow HSC appears to be regulated by highly specific transcriptional mechanisms that remain largely unknown. The progeny of self-renewing HSC initiate ordered differentiation programs that give rise to all blood lineages. In particular, the development of B and T lymphocytes involves a massive proliferative expansion of immature precursors. Both HSC self-renewal and lymphocyte expansion appear exquisitely sensitive to elevated levels of the cell] cycle inhibitor p16lnk4a, which is actively repressed by poorly defined molecular pathways. Our studies of hematopoiesis focused on Zfx, an evolutionarily conserved zinc finger-containing transcription factor. In preliminary experiments, inactivation of murine Zfx in the hematopoietic system leads to a specific loss of adult bone marrow HSC population. In addition, the expansion of immature B and T lymphocytes was severely impaired. Preliminary expression analysis suggests that these phenotypes might be caused by the overexpression of p16lnk4a in the absence of Zfx. Therefore, Zfx might represent an essential and specific positive regulator of HSC self-renewal and of immature lymphocyte expansion upstream of p16lnk4a. To test this hypothesis, three Specific Aims are proposed. First, the role of Zfx in HSC self-renewal will be characterized at the functional level. Second, early development and growth of Zfx-deficient lymphocytes will be investigated. Third, the molecular basis of Zfx activity will be established through the identification and functional analysis of its target genes in hematopoietic cells. These studies might identify novel molecular mechanisms that facilitate the maintenance of HSC and of immature lymphocytes, possibly through the repression of p16lnk4a.