Zfx, A Novel Transcriptional Regulator of Hematopoiesis

描述（由申请人提供）：哺乳动物造血是基于造血干细胞（HSC）的活性，在整个成年期进行持续的自我更新。骨髓HSC的长期维持似乎是由高度特异性的转录机制调控的，这在很大程度上仍是未知的。自我更新的造血干细胞的后代启动有序分化程序，产生所有血统。特别是，B淋巴细胞和T淋巴细胞的发育涉及未成熟前体的大量增殖扩张。HSC自我更新和淋巴细胞扩增对细胞周期抑制剂p16lnk4a水平的升高非常敏感，p16lnk4a被不明确的分子途径积极抑制。我们对造血的研究集中在Zfx，一个进化上保守的含锌指的转录因子。在初步实验中，小鼠造血系统中Zfx的失活导致成人骨髓HSC群体的特异性损失。此外，未成熟B淋巴细胞和T淋巴细胞的扩张严重受损。初步的表达分析表明，这些表型可能是在缺乏Zfx的情况下p16lnk4a过表达引起的。因此，Zfx可能是p16lnk4a上游HSC自我更新和未成熟淋巴细胞扩增的重要特异性正调节因子。为了验证这一假设，提出了三个具体目标。首先，Zfx在HSC自我更新中的作用将在功能水平上进行表征。其次，研究zfx缺陷淋巴细胞的早期发育和生长。第三，通过对Zfx在造血细胞中的靶基因的鉴定和功能分析，建立Zfx活性的分子基础。这些研究可能发现促进HSC和未成熟淋巴细胞维持的新的分子机制，可能通过抑制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.