Placenta as a novel site for hematopoietic stem cells

描述（由申请人提供）：我们的目标是定义控制造血干细胞（HSC）发生的发育途径。本研究的主要目的是探讨胎盘在造血干细胞发育中的作用。我们的假设是，胎盘有助于胎儿时期造血干细胞的形成、成熟和/或扩增，因此可能代表了一个重要的、以前未被认识到的HSC发育位点。我们的颞叶移植研究表明妊娠中期胎盘中主要的HSC生态位的发展。1)我们现在将通过将胎盘和胎儿造血器官的细胞群移植到辐照的成人受体中来确定胎盘中造血干细胞的免疫表型。2)随后，我们将通过免疫组织化学和共聚焦显微镜确定胎盘造血干细胞及其在胎盘切片中的假定前体的空间定位，使用将通过移植定义的标记物，并通过分析靶向关键造血转录因子SCL或runxl/AML1基因的小鼠品系。3)通过建立胎盘外植体培养，我们将研究造血干细胞是在胎盘中从头生成还是从其他地方播种，并研究胎盘微环境是否支持造血干细胞成熟和扩增。如果我们能够通过外植体培养的功能评估来鉴定造血干细胞的前体，我们将最终通过表达谱来比较这些与发育相关但功能不同的造血细胞群。我们的目标是确定与重建成人骨髓和确定造血室干性能力相关的分子程序。我们相信，我们的研究不仅将澄清胚胎发生过程中造血干细胞起源的争议，而且有助于确定支持造血干细胞发生、成熟和扩增的细胞自主和微环境因素。如果在胚胎发育过程中促进造血干细胞“干性”的微环境因素可以在体外胎盘外植体培养中诱导造血干细胞成熟和扩增，那么这种培养系统可能用于产生或扩增用于治疗目的的人造血干细胞。

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.