ROLE OF THE CHROMATIN REGULATOR, MLL, IN T CELL DEVELOPMENT

染色质调节因子 MLL 在 T 细胞发育中的作用

• 批准号: 7720751
• 负责人: Patricia Ernst
• 金额: $ 23.51万
• 依托单位: DARTMOUTH COLLEGE
• 依托单位国家: 美国
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-01 至 2009-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7720751
• 关键词: Acute; Acute Lymphocytic Leukemia; Acute T Cell Leukemia; Adult; Animals; Area; B-Lymphocytes; Backcrossings; Biological Models; Bone Marrow; Bone Marrow Cells; Cell Count; Cells; Cessation of life; Chromatin; Computer Retrieval of Information on Scientific Projects Database; Coupled; Development; Double-Stranded RNA; Embryo; Erythroid; Fetal Liver; Funding; Genes; Goals; Grant; Greater sac of peritoneum; Hematopoiesis; Hematopoietic; Hematopoietic System; Hematopoietic stem cells; Infant; Injection of therapeutic agent; Institution; Lymphoid; Lymphopoiesis; Maintenance; Manuscripts; Modeling; Mouse Strains; Muramidase; Mus; Pancytopenia; Patients; Phenotype; Population; Research; Research Personnel; Resources; Role; Source; Stem cells; T-Lymphocyte; Transgenes; Transgenic Animals; Transgenic Organisms; United States National Institutes of Health; analog; cell type; day; exhaustion; interest; mature animal; primitive cell; progenitor; recombinase; research study; size; stem

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. To develop model systems in which the role of MLL can be assessed during adult hematopoiesis and lymphopoiesis, we have developed a loxP-flanked version of the murine Mll gene, backcrossed this strain, and crossed it to the Mx1-Cre transgenic strain. The Mx1 transgene is induced by the injection of polyI:polyC, a double stranded RNA analog that can be injected into the peritoneal cavity of adult animals. This approach allowed us to study the effect of Mll deletion in an acute setting. Using this model, we demonstrated that the maintenance of hematopoietic stem and progenitor populations depend on Mll for their homoestasis. We demonstrated that this was likely due to two different cell-context dependent roles of Mll in these primitive cell types. First, Mll deletion in hematopoietic stem cells resulted in their escape from quiescence and an increase in proliferation, coupled to symmetric differentiation of progeny cells. This resulted in the rapid exhaustion of stem cell activity from the bone marrow. Second, we demonstrated that in myelo-erythroid progenitors, Mll deficiency resulted in the reduction in proliferation resulting in reduced progenitor pool sizes. Together, these alterations resulted in the rapid decline in bone marrow cell numbers upon Mll deletion and ultimately bone marrow failure and animal death. Surprisingly, when we crossed the Mll loxP flanked strain to Cre transgenic animals that express Cre only in differentiating lineages (T cells [lck-Cre], B cells [CD19-Cre] or myelomonocytic precursors [lysozyme M-Cre]), we found that there was no effect on steady state cell numbers, demonstrating that Mll is only essential in the early stem and progenitor populations. Progress toward the main goal of this Project has been great in the area of lymphopoiesis. We are currently finishing experiments that will form the bulk of a manuscript that defines a block in B lymphopoiesis in the absence of Mll. To perform these studies, we obtained a Vav-Cre strain of mice from Dr. T. Graf (via Dr. H. Mikkola). This strain expresses the Cre recombinase within the hematopoietic system starting at embryonic day 13 in the fetal liver. Using this approach, we are able to study the early steps in commitment to the lymphoid lineages (T and B cells) which was not possible using the Mx1-Cre strain used in the studies described above, due to the confounding effects of polyI:polyC injection. With the Vav-cre model, we observe a stringent requirement for MLL in B lymphopoiesis but not T lymphopoiesis. This is interesting since patients with MLL translocations, particularly infants, have acute lymphocytic leukemia (ALL) of an early B cell phenotype and T cell ALL is very rare.

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 为了开发模型系统，其中MLL的作用可以在成人造血和淋巴细胞生成过程中进行评估，我们已经开发了loxP侧翼的版本的鼠Mll基因，回交该菌株，并将其杂交到Mx 1-Cre转基因菌株。 Mx 1转基因是通过注射polyI：polyC诱导的，polyI：polyC是一种双链RNA类似物，可以注射到成年动物的腹膜腔中。 这种方法允许我们研究MII缺失在急性环境中的作用。 使用该模型，我们证明了造血干细胞和祖细胞群体的维持依赖于MII的同源稳态。 我们证明，这可能是由于MII在这些原始细胞类型中的两种不同的细胞环境依赖性作用。 首先，造血干细胞中的MII缺失导致它们从静止中逃逸并增加增殖，与子代细胞的对称分化偶联。 这导致骨髓中的干细胞活性迅速耗尽。 其次，我们证明了在骨髓-红系祖细胞中，MII缺乏导致增殖减少，从而导致祖细胞库大小减少。 总之，这些改变导致MII缺失后骨髓细胞数量迅速下降，最终导致骨髓衰竭和动物死亡。 令人惊讶的是，当我们将MII loxP侧翼菌株与仅在分化谱系（T细胞[lck-Cre]、B细胞[CD 19-Cre]或骨髓单核细胞前体[溶菌酶M-Cre]）中表达Cre的Cre转基因动物杂交时，我们发现对稳态细胞数量没有影响，证明MII仅在早期干细胞和祖细胞群体中是必需的。 该项目的主要目标在淋巴细胞生成领域取得了巨大进展。 我们目前正在完成的实验，将形成一个手稿的大部分，定义了一个块在B淋巴细胞生成在MII的情况下。 为了进行这些研究，我们从T博士那里获得了Vav-Cre小鼠品系。格拉夫（通过H. Mikkola）。 该菌株在胚胎第13天开始在胎儿肝脏中的造血系统内表达Cre重组酶。 使用这种方法，我们能够研究向淋巴谱系（T和B细胞）定型的早期步骤，由于polyI：polyC注射的混杂效应，使用上述研究中使用的Mx 1-Cre菌株是不可能的。在Vav-cre模型中，我们观察到B淋巴细胞生成对MLL的严格要求，而T淋巴细胞生成则没有。 这是有趣的，因为患有MLL易位的患者，特别是婴儿，患有早期B细胞表型的急性淋巴细胞白血病（ALL），而T细胞ALL非常罕见。