Department of Developmental Genetics, Max Planck Institute for Heart and Lung Research, Bad Nauheim, Germany.
Blood. 2018 Mar 1;131(9):963-973. doi: 10.1182/blood-2017-07-797795. Epub 2018 Jan 16.
During development, hematopoietic stem cells (HSCs) derive from specialized endothelial cells (ECs) called hemogenic endothelium (HE) via a process called endothelial-to-hematopoietic transition (EHT). Hypoxia-inducible factor-1α (HIF-1α) has been reported to positively modulate EHT in vivo, but current data indicate the existence of other regulators of this process. Here we show that in zebrafish, Hif-2α also positively modulates HSC formation. Specifically, HSC marker gene expression is strongly decreased in () and in () zebrafish mutants and morphants. Moreover, live imaging studies reveal a positive role for and in regulating HE specification. Knockdown of in mutants leads to a greater decrease in HSC formation, indicating that and have partially overlapping roles in EHT. Furthermore, hypoxic conditions, which strongly stimulate HSC formation in wild-type animals, have little effect in the combined absence of Hif-1α and Hif-2α function. In addition, we present evidence for Hif and Notch working in the same pathway upstream of EHT. Both and mutants display impaired EHT, which cannot be rescued by hypoxia. However, overexpression of the Notch intracellular domain in ECs is sufficient to rescue the and morphant EHT phenotype, suggesting that Notch signaling functions downstream of the Hif pathway during HSC formation. Altogether, our data provide genetic evidence that both Hif-1α and Hif-2α regulate EHT upstream of Notch signaling.
在发育过程中，造血干细胞（HSCs）通过内皮细胞到造血的转变（EHT）过程从称为造血内皮细胞（HE）的特殊内皮细胞中产生。已经报道缺氧诱导因子-1α（HIF-1α）在体内正向调节 EHT，但目前的数据表明存在该过程的其他调节剂。在这里，我们表明在斑马鱼中，Hif-2α也正向调节 HSC 的形成。具体来说，HSC 标记基因的表达在 （）和 （）斑马鱼突变体和嵌合体中强烈降低。此外，活体成像研究揭示了 和 在调节 HE 特化中的积极作用。在 突变体中敲低 会导致 HSC 形成更大的减少，表明 和 在 EHT 中具有部分重叠的作用。此外，强烈刺激野生型动物中 HSC 形成的低氧条件对 Hif-1α和 Hif-2α功能的联合缺失几乎没有影响。此外，我们提供了证据表明 Hif 和 Notch 在 EHT 的上游在同一途径中起作用。 和 突变体均显示 EHT 受损，缺氧不能挽救。然而，在 ECs 中过表达 Notch 细胞内结构域足以挽救 和 嵌合体 EHT 表型，表明 Notch 信号在 HSC 形成过程中在 Hif 途径下游起作用。总而言之，我们的数据提供了遗传证据，表明 Hif-1α和 Hif-2α都在上游 Notch 信号调节 EHT。
