Control of Hematopoiesis by AP-1 and Bcl6

造血干细胞的增殖和分化受转录因子的调控。在本研究中，我们利用转基因小鼠分析了AP-1和Bcl6两个直接早期基因家族的作用，并敲除了小鼠。c-Fos与Jun家族形成AP-1复合体，调节AP-1结合基因的表达。在细胞因子刺激的原始造血干细胞中，c-fos瞬时上调。为了研究c-fos在造血中的作用，我们使用了在干扰素诱导的Mx-启动子(Mx-c-fos)和c-fos缺陷小鼠的控制下携带c-fos基因的转基因小鼠。C-fos在造血干细胞中的长时间表达使其处于细胞周期的G0/G1期，从而抑制了因子依赖型集落形成和基质依赖型造血。这些结果表明，c-fos诱导的I期造血干细胞对S细胞周期进程具有负性调控作用，并使其处于休眠状态。bcl6基因已从t-…中获得B细胞淋巴瘤中更多的染色体易位断裂点及其产物作为序列特异性转录抑制物发挥作用。Bcl6对生发中心B细胞的分化起关键作用。为了分析Bcl6在B细胞发育中的作用，我们使用了一种高效的逆转录病毒转导系统来转导小鼠造血干细胞。我们构建了表达小鼠Bcl6和增强型绿色荧光蛋白(EGFP)的双顺反子逆转录病毒。用该病毒感染LIN-SCA-1^+BM细胞，在有SCF和IL-6存在的情况下，分选EGFP^+细胞注入2.5Gy射线照射的SCID小鼠或与OP-9基质细胞共培养。感染对照病毒(MSCV-EGFP)的BM细胞在体内和体外均能增殖并分化为B细胞和髓系细胞。感染Bcl6病毒的骨髓细胞(MSCV-EGFP-Bcl6)可分化为髓系细胞，但B细胞分化受阻。尽管存在高表达EGFP的髓系细胞，但表达EGFP的B细胞很少或缺乏。另一方面，缺乏Bcl6的造血干细胞可以同时分化为髓系细胞和B淋巴样细胞。这些结果表明，Bcl6的表达可以用来确定造血系统中不同的细胞命运。较少

Proliferation and differentiation of hematopoietic stem cells are regulated by transcriptional factors. In this study, we have analyzed role of two immediated early gene families, AP-1 and Bcl6 using transgenic mice and knock out mice.c-Fos forms AP-1 complex with Jun family and regulates the expression of AP-1 binding genes. c-fos is transiently upregulated in primitive hematopoietic stem cells stimulated with cytokines. To investigate the role of c-fos in hematopoiesis, we used transgenic mice carrying the c-fos gene under the control of the interferon-inducible Mx-promoter (Mx-c-fos) and c-fos deficient mice. Prolonged expression of c-fos in hematopoietic stem cells inhibited factor dependent colony formation and stroma dependent hematopoiesis by keeping them at G0/G1 phase of the cell cycle. These result suggest that the c-fos induced i hematopoietic stem cells negatively control s cell cycle progression and maintains them in a dormant state.The Bcl6 gene has been identified from t … More he chromosomal translocation breakpoint in B-cell lymphoma and its product functions as a sequence-specific transcriptional repressor. Bcl6 is critical for the differentiation of germinal center B cell. To analyze the function of Bcl6 in B cell development, we used an efficient retroviral transduction system to murine hematopoietic stem cells. We constructed a bicistronic retrovirus expressing the murine Bcl6 and the enhanced green fluorescent protein (EGFP). Lin-Sca-1^+ BM cells (hematopoietic stem cell fraction) were infected with this virus in the presence of SCF and IL-6, and EGFP^+ cells were sorted and injected into the 2.5 Gy irradiated SCID mice or co-cultured on OP-9 stromal cells with or without IL-7. BM cells infected with a control virus (MSCV-EGFP) proliferated and differentiated into B cells and myeloid cells both in vivo and in vitro. BM cells infected with the Bcl6 virus (MSCV-EGFP-Bcl6) differentiated into myeloid cells, but B cell differentiation was impaired. Although myeloid cells expressed high level of EGFP were developed, B cells developed were low or lack in EGFP.On the other hand, hematopoietic stem cells lacking Bcl6 could differentiate into both myeloid and B lymhoid cells. These results suggest that expression of Bcl6 can be used to specify distinct cell fates in the hematopoietic system. Less