造血干细胞（HSC）是目前研究最为广泛的成体干细胞类型，其造血稳态受内外多种因素调节，其中转录因子发挥了重要的作用。然而HSC如何利用转录因子正确地调控其自我更新和定向分化，以及维持其自身静息状态的具体分子机制目前尚不明确。我们前期的研究发现，HSC在白血病环境下受抑，并发现Egr转录因子家族基因（Early growth response gene）在受抑的HSC中高表达（包括Egr1，Egr2和Egr3），尤其以Egr3变化最为明显，提示我们Egr3可能是HSC受抑的原因。进一步研究发现，高表达Egr3能阻滞HSC的增殖，使其更多的处于细胞周期G0期；相反，敲降Egr3能增强HSC的增殖能力。因此，本课题主要利用过表达和条件性敲除Egr3双向实验，全面阐释其调控HSC数量与功能的分子机制，以期寻找抑制与增强造血干细胞功能的分子网络，为增强造血干细胞的功能提供新的分子靶点。

The hematopoietic stem cell (HSC) is probably the most widely used and the best understood somatic stem cell in higher organisms. Its homeostasis is governed by both intrinsic and extrinsic factors. The transcription factors (TFs) has been implicated in regulating HSC function. However, how the TFs controlling HSC self-renewal, differentiation commitment and quiescence remain poorly characterized. Our recent study showed that HSC was suppressed in leukemic environment, and the early growth response (Egr) transcriptional family genes (including Egr1, Egr2 and Egr3) were upregulated in suppressed HSC. Compared with Egr1 and Egr2, Egr3 showed the most significant increases in expression level, suggesting that Egr3 may be responsible for HSC suppression in leukemia. Our further results showed that Egr3 overexpression restricted the proliferation of HSC and led to an approximately 60% increase in cells in G0 phase compared with control, while reducing Egr3 expression using shRNA was able to promote HSC proliferation. Thus, in the project, combining of overexpression assay and conditional knockout mouse model, we will study the impact of Egr3 on HSC function, and explore the underlying molecular mechanisms. Our study will identify potential key regulators of HSC and offers promise for a new therapeutic target for clinically application of HSC.