Investigating the role of the miR-125b target ARID3A in the pathology of myeloid leukemia associated with Down syndrome

唐氏综合征相关髓性白血病（ML-DS）的特征是21三体、胎儿起源和GATA1突变（GATA1s突变）。我们之前发现21号染色体上的miR-99a~125b三联体成员（miR-125b-2， miR-99a和let-7c）在ML-DS中过表达。然而，miR-99a~125b过表达与GATA1s在疾病发生和进展中的协同作用尚不清楚。使用基于荧光的慢病毒条形码系统来绘制基因编辑的胎儿造血干细胞/肝脏祖细胞（FLCs）中的遗传相互作用，我们观察到Gata1s和miR-125b的组合在体外协同增加未成熟巨核细胞祖细胞的增殖，并促进体内白血病的发生。miR-99a~125b三联体的其他成员单独或联合均不能诱导这种作用。基于shrna的阳性选择筛选数据和在Gata1s- flcs中开启和关闭miR-125b后基因表达变化的综合分析表明，Arid3a是miR-125b驱动其与Gata1s协同作用的主要靶点。ARID3a （AT-Rich Interaction Domain 3A；别名：Bright）是一种转录因子，与多种过程的控制有关，包括胚胎发育和早期造血。该项目的目的是了解ARID3a在胎儿造血中的功能，并描述其在人髓性白血病发病机制中的作用，特别是其在TAM和ML-DS中与Gata1s的协同作用。为了实现这一目标，我们需要(1)确立Arid3a作为miR-125b的直接靶点和Gata1s在白血病发生中的合作伙伴，(2)在体外和体内研究Arid3a在正常和恶性造血细胞中的作用，(3)利用最新技术揭示Arid3a的分子功能和相互作用网络。我们新开发的小鼠Gata1s白血病前期模型，以及我们的患者来源异种移植物（PDX）库，为我们实现这一目标提供了前所未有的新途径。利用这些资源，我们将能够通过蛋白质编码基因和非编码基因之间的相互作用，为理解造血和肿瘤发生的上位性协调迈出决定性的一步。

Down syndrome-associated myeloid leukemia (ML-DS) is characterized by the triad of trisomy 21, fetal origin and mutations in GATA1 (GATA1s mutations). We previously found that members of the miR-99a~125b tricistron (miR-125b-2, miR-99a and let-7c) on chromosome 21 are overexpressed in ML-DS. However, the synergy between miR-99a~125b overexpression and GATA1s in disease initiation and progression remains unclear. Using a fluorescence-based lentiviral barcoding system to map genetic interactions in gene-edited fetal hematopoietic stem/progenitor cells from the liver (FLCs), we observed that the combination of Gata1s and miR-125b synergized to increase the proliferation of immature megakaryocytic progenitor cells in vitro and promote leukemogenesis in vivo. Other members of the miR-99a~125b tricistron did not induce such effects either alone or in combination. Integrative analysis of shRNA-based positive selection screening data and gene expression changes upon switching miR-125b on and off in Gata1s-FLCs suggested Arid3a as the main target of miR-125b that drives its synergy with Gata1s. ARID3a (AT-Rich Interaction Domain 3A; alias: Bright) is a transcription factor that has been implicated in the control of a variety of processes, including embryonic development and early hematopoiesis. The aim of this project is to understand the function of ARID3a in fetal hematopoiesis and delineate its role in the pathogenesis of human myeloid leukemia – particularly its synergy with Gata1s in TAM and ML-DS. This goal is to be achieved by (1) establishing Arid3a as a direct target of miR-125b and a cooperating partner of Gata1s in leukemogenesis, (2) investigating the role of ARID3A in normal and malignant hematopoietic cells in vitro and in vivo and (3) uncovering the molecular function and interaction network of ARID3A with state-of-the-art technologies. Our newly developed murine Gata1s preleukemic model, together with our patient-derived xenograft (PDX) bank, offer us new, previously unprecedented avenues to achieving this goal. Using these resources, we will be able to contribute a decisive step towards understanding the epistatic coordination of hematopoiesis and oncogenesis through interactions between protein-coding and non-coding genes.