Induction of a hemogenic program in mouse fibroblasts

Definitive hematopoiesis emerges during embryogenesis via an endothelial-to-hematopoietic transition. We attempted to induce this process in mouse fibroblasts by screening a panel of factors for hemogenic activity. We identified a combination of four transcription factors, Gata2, Gfi1b, cFos, and Etv6 that efficiently induces endothelial-like precursor cells with the subsequent appearance of hematopoietic cells. The precursor cells express a human CD34 reporter, Sca1 and Prominin1 within a global endothelial transcription program. Emergent hematopoietic cells possess nascent/specifying hematopoietic stem cell gene expression profiles and cell surface phenotypes. After transgene silencing and reaggregation culture, the specified cells generate hematopoietic colonies in vitro. Thus, we have shown that a simple combination of transcription factors is sufficient to induce a complex, dynamic and multi-step developmental program in vitro. These findings provide insights into the specification of definitive hemogenesis and a platform for future development of patient-specific stem/progenitor cells as well as more differentiated blood products.

定型造血（Definitive Hematopoiesis）在胚胎发生过程中通过内皮向造血转化（endothelial-to-hematopoietic transition）过程产生。本研究尝试在小鼠成纤维细胞中诱导该过程，通过筛选一组因子以评估其生血活性。我们鉴定出由Gata2、Gfi1b、cFos和Etv6四种转录因子（transcription factors）组成的组合，该组合可高效诱导生成类内皮前体细胞，并后续产生造血细胞。该前体细胞在整体内皮转录程序框架下表达人CD34报告基因、Sca1及Prominin1。新生造血细胞具有处于形成/特化阶段的造血干细胞基因表达谱与细胞表面表型。在外源转基因沉默并进行重聚集培养后，这些特化细胞可在体外生成造血集落。综上，本研究证实，仅需简单的转录因子组合即可在体外诱导出复杂、动态且多步骤的发育程序。本研究结果为定型造血发生的特化机制提供了新的见解，并为未来开发患者特异性干/祖细胞以及更高分化程度的血液制品搭建了研究平台。