Differential Ezh1/2 regulation of hemogenic fate and hematopoietic stem and progenitor cell formation from arterial endothelium

Across species, hematopoietic stem and progenitor cells (HSPCs) arise during embryogenesis from a specialized arterial population, termed hemogenic endothelium. Here, we describe a mechanistic role for the epigenetic regulator, Enhancer of zeste homolog-1 (Ezh1) in vertebrate HSPC production via regulation of hemogenic commitment. Loss of ezh1 in zebrafish embryos favored acquisition of hemogenic (gata2b) and HSPC (runx1) fate at the expense of the arterial program (ephrinb2a, dll4). In contrast, ezh1 overexpression blocked hematopoietic progression via maintenance of arterial gene expression. The related polycomb group subunit, Ezh2, functioned in a non-redundant, sequential manner, whereby inhibition had no impact on arterial identity, but was capable of blocking ezh1-knockdown associated HSPC expansion. Single-cell RNA-seq across ezh1 genotypes revealed a dropout of ezh1+/- cells among arterial endothelium associated with positive regulation of gene transcription. Exploitation of Ezh1/2 modulation has potential functional relevance for improving in vitro HSPC differentiation from induced pluripotent stem cell sources.

跨物种而言，造血干细胞和祖细胞（hematopoietic stem and progenitor cells, HSPCs）在胚胎发生过程中源自一类被称为生血内皮（hemogenic endothelium）的特化动脉群体。本研究阐明了表观遗传调控因子zeste基因增强子同源物1（Enhancer of zeste homolog-1, Ezh1）通过调控生血定向分化，在脊椎动物HSPC生成过程中的作用机制。斑马鱼胚胎中ezh1的缺失会促进生血相关基因gata2b以及HSPC相关基因runx1的命运确立，却以牺牲动脉程序相关基因ephrinb2a、dll4的表达为代价；与之相反，ezh1过表达则通过维持动脉基因的表达阻断造血进程。与其同源的多梳蛋白家族（polycomb group, PcG）亚基Ezh2以非冗余的时序模式发挥功能：抑制Ezh2不会对动脉细胞身份造成影响，但能够阻断ezh1敲低所引发的HSPC扩增。对不同ezh1基因型样本开展单细胞RNA测序（single-cell RNA-seq, scRNA-seq）后发现，动脉内皮细胞群中ezh1+/-细胞出现丢失，该现象与基因转录的正向调控存在关联。调控Ezh1/2活性的手段，或可用于优化诱导多能干细胞（induced pluripotent stem cell, iPSC）体外定向分化为HSPC的实验体系，具备潜在的应用价值。