During development, erythroid cells are generated by two waves of hematopoiesis. In zebrafish, primitive erythropoiesis takes place in the intermediate cell mass region, and definitive erythropoiesis arises from the aorta-gonad mesonephros. TALE-homeoproteins Meis1 and Pbx1 function upstream of GATA1 to specify the erythroid lineage. Embryos lacking Meis1 or Pbx1 have weak gata1 expression and fail to produce primitive erythrocytes. Nevertheless, the underlying mechanism of how Meis1 and Pbx1 mediate gata1 transcription in erythrocytes remains unclear. Here we show that Hif1α acts downstream of Meis1 to mediate gata1 expression in zebrafish embryos. Inhibition of Meis1 expression resulted in suppression of hif1a expression and abrogated primitive erythropoiesis, while injection with in vitro-synthesized hif1α mRNA rescued gata1 transcription in Meis1 morphants and recovered their erythropoiesis. Ablation of Hif1α expression either by morpholino knockdown or Crispr-Cas9 knockout suppressed gata1 transcription and abrogated primitive erythropoiesis. Results of chromatin immunoprecipitation assays showed that Hif1α associates with hypoxia-response elements located in the 3′-flanking region of gata1 during development, suggesting that Hif1α regulates gata1 expression in vivo. Together, our results indicate that Meis1, Hif1α, and GATA1 indeed comprise a hierarchical regulatory network in which Hif1α acts downstream of Meis1 to activate gata1 transcription through direct interactions with its cis-acting elements in primitive erythrocytes.

中文翻译：

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Meis1、Hi1α 和 GATA1 被整合到一个层次化的调控网络中以介导原始红细胞生成

在发育过程中，红细胞由两波造血波产生。在斑马鱼中，原始红细胞生成发生在中间细胞团区域，最终红细胞生成来自主动脉 - 性腺中肾。TALE-homeoproteins Meis1 和 Pbx1 在 GATA1 上游起作用以指定红细胞谱系。缺乏MEIS1或PBX1胚胎具有弱GATA1表达和不能产生原始红细胞。尽管如此，MEIS1和PBX1中介如何的基本机制GATA1红细胞转录仍不清楚。在这里，我们表明HIF1α行为MEIS1下游调解GATA1表达的斑马鱼胚胎。抑制 Meis1 表达导致抑制hif1a表达和废止原始红细胞生成，而注射在体外合成的HIF1α基因救出GATA1在MEIS1 morphants转录和回收它们的红细胞生成。或者通过吗啉击倒或CRISPR-Cas9HIF1α表达的消融敲除抑制GATA1转录和废止原始红细胞生成。染色质免疫沉淀测定法的结果表明，相关联HIF1α与位于的3'-侧翼区缺氧反应元件GATA1发育过程中，这表明HIF1α调节GATA1体内表达。总之，我们的结果表明，MEIS1，HIF1α和GATA1确实包含其中HIF1α行为MEIS1下游激活层次监管网络GATA1通过与其直接相互作用的转录顺式作用的原始红细胞元素。