Department of Pediatrics, Tulane University School of Medicine, New Orleans, Louisiana, USA.
Department of Obstetrics & Gynecology, Tulane University School of Medicine, New Orleans, Louisiana, USA.
J Biol Chem. 2020 Aug 14;295(33):11542-11558. doi: 10.1074/jbc.RA120.013348. Epub 2020 Jun 18.
SIX2 (SIX homeobox 2)-positive nephron progenitor cells (NPCs) give rise to all epithelial cell types of the nephron, the filtering unit of the kidney. NPCs have a limited lifespan and are depleted near the time of birth. Epigenetic factors are implicated in the maintenance of organ-restricted progenitors such as NPCs, but the chromatin-based mechanisms are incompletely understood. Here, using a combination of gene targeting, chromatin profiling, and single-cell RNA analysis, we examined the role of the murine histone 3 Lys-27 (H3K27) methyltransferases EZH1 (enhancer of zeste 1) and EZH2 in NPC maintenance. We found that EZH2 expression correlates with NPC growth potential and that EZH2 is the dominant H3K27 methyltransferase in NPCs and epithelial descendants. Surprisingly, NPCs lacking H3K27 trimethylation maintained their progenitor state but cycled slowly, leading to a smaller NPC pool and formation of fewer nephrons. Unlike loss of function, dual inactivation of and triggered overexpression of the transcriptional repressor Hes-related family BHLH transcription factor with YRPW motif 1 (), down-regulation of , and unscheduled activation of Wnt4-driven differentiation, resulting in early termination of nephrogenesis and severe renal dysgenesis. Double-mutant NPCs also overexpressed the SIX family member However, in this context, SIX1 failed to maintain NPC stemness. At the chromatin level, EZH1 and EZH2 restricted accessibility to AP-1-binding motifs, and their absence promoted a regulatory landscape akin to differentiated and nonlineage cells. We conclude that EZH2 is required for NPC renewal potential and that tempering of the differentiation program requires cooperation of both EZH1 and EZH2.
SIX2（SIX 同源盒 2）阳性肾祖细胞（NPC）产生肾脏过滤单位——肾单位的所有上皮细胞类型。NPC 的寿命有限，在接近出生时耗尽。表观遗传因素与 NPC 等器官特异性祖细胞的维持有关，但基于染色质的机制尚不完全清楚。在这里，我们使用基因靶向、染色质谱分析和单细胞 RNA 分析相结合的方法，研究了小鼠组蛋白 3 赖氨酸 27（H3K27）甲基转移酶 EZH1（增强子结合锌指蛋白 1）和 EZH2 在 NPC 维持中的作用。我们发现 EZH2 的表达与 NPC 生长潜力相关，EZH2 是 NPC 和上皮后代中主要的 H3K27 甲基转移酶。令人惊讶的是，缺乏 H3K27 三甲基化的 NPC 保持其祖细胞状态，但周期缓慢，导致 NPC 池较小，形成的肾单位较少。与功能丧失不同，和的双重失活触发了转录抑制因子 Hes 相关家族碱性螺旋-环-螺旋转录因子 1（）的过表达、下调、以及未计划的 Wnt4 驱动的分化激活，导致肾发生早期终止和严重的肾发育不良。双突变 NPC 还过表达 SIX 家族成员 SIX1 然而，在这种情况下，SIX1 未能维持 NPC 干细胞特性。在染色质水平上，EZH1 和 EZH2 限制了 AP-1 结合基序的可及性，它们的缺失促进了类似于分化和非谱系细胞的调控景观。我们得出结论，EZH2 是 NPC 更新潜力所必需的，而分化程序的缓和需要 EZH1 和 EZH2 的合作。
