Placenta as a novel site for hematopoietic stem cells

描述(由申请人提供)：我们的目标是确定控制造血干细胞(HSC)发生的发育途径。这项建议的主要目的是研究胎盘在造血干细胞发育中的作用。我们的假设是，胎盘有助于造血干细胞在胎儿时期的形成、成熟和/或扩增，因此可能是一个重要的、以前未被认识的HSC发育部位。我们的颞叶移植研究表明，在妊娠中期胎盘中有一个主要的HSC生态位的发育。1)我们将从胎盘和胎儿造血器官分离的细胞群移植到照射的成年受者体内，以确定胎盘中HSCs的免疫表型。2)随后，我们将通过免疫组织化学和共聚焦显微镜来确定胎盘HSCs及其可能的前体细胞在胎盘切片中的空间定位，方法是使用移植所定义的标记，并通过分析以关键造血转录因子SC1或runx1/AML1基因为靶点的小鼠品系。3)通过建立胎盘外植体培养，我们将研究HSC是在胎盘中产生还是从其他地方种植，并研究胎盘微环境是否支持HSC的成熟和扩增。如果我们能够通过外植体培养中的功能评估来确定HSCs的前体，我们最终将通过表达谱来比较这些发育相关但功能不同的造血细胞群体。我们的目标是确定与重建成人骨髓的能力相关的分子程序，并确定造血室中的干细胞。我们相信，我们的研究不仅将澄清胚胎发育过程中关于HSC起源的争议，还将有助于识别支持HSC发生、成熟和扩增的细胞自主和微环境因素。如果能够利用在胚胎发育过程中促进HSCs“干化”的微环境因子，在胎盘外植体培养上诱导HSC的成熟和体外扩增，该培养体系可能被用于产生或扩增用于治疗目的的HSCs。

DESCRIPTION (provided by applicant): Our aim is to define developmental pathways that govern the genesis of hematopoietic stem cells (HSC). The main goal of this proposal is to investigate the role of placenta in hematopoietic stem cell development. Our hypothesis is that placenta contributes to the formation, maturation and/or expansion of hematopoietic stem cells during fetal life, and thus may represent an important, previously unrecognized site for HSC development. Our temporal transplantation studies have shown a development of a major HSC niche in placenta during midgestation. 1) We will now define the immunophenotype of HSCs in placenta by transplantation of sorted cell populations from placenta and fetal hematopoietic organs into irradiated adult recipients. 2) Subsequently, we will define the spatial localization of placenta HSCs and their putative precursors in placenta sections by immunohistochemistry and confocal microscopy by using markers that will be defined by transplantation and by analyzing mouse strains where genes for critical hematopoietic transcription factors SCL or runxl/AML1 have been targeted. 3) By establishing placenta explant cultures we will address whether HSCs are generated de novo in placenta or seeded from elsewhere and investigate whether placenta microenvironment can support HSC maturation and expansion. If we can identify precursors for HSCs by functional assessment in explant cultures, we will ultimately compare these developmentally related but functionally distinct hematopoietic cell populations by expression profiling. Our goal is to identify molecular programs that are associated with the ability to reconstitute adult bone marrow and define stemness in the hematopoietic compartment. We believe that our studies will not only clarify the controversy of HSC origin during embryogenesis but also help to identify cell autonomous and microenvironmental factors supporting the genesis, maturation, and expansion of HSCs. If microenvironmental factors promoting "stemness" of HSCs during embryonic development can be harnessed to induce HSC maturation and expansion in vitro on placenta explant cultures, this culture system might potentially be used to generate or expand human HSCs for therapeutic purposes.