Existing knowledge of the role of epigenetic modifiers in pancreas development has exponentially increased. However, the function of TET dioxygenases in pancreatic endocrine specification remains obscure. We set out to tackle this issue using a human embryonic stem cell (hESC) differentiation system, in which TET1/TET2/TET3 triple knock-out cells display severe defects in pancreatic β-cell specification. Integrative whole-genome analysis identifies unique cell-type-specific hypermethylated regions (hyper-DMRs) displaying reduced chromatin activity and remarkable enrichment of FOXA2, a pioneer transcription factor essential for pancreatic endoderm specification. Intriguingly, TET depletion leads to significant changes in FOXA2 binding at pancreatic progenitor stage, in which gene loci with decreased FOXA2 binding features low levels of active chromatin modifications and enriches for bHLH motifs. Transduction of full-length TET1 but not the TET1-catalytic-domain in TET-deficient cells effectively rescues β-cell differentiation accompanied by restoring PAX4 hypomethylation. Taking these findings together with the defective generation of functional β-cells upon TET1-inactivation, our study unveils an essential role of TET1-dependent demethylation in establishing β-cell identity. Moreover, we discover a physical interaction between TET1 and FOXA2 in endodermal lineage intermediates, which provides a new mechanistic clue regarding the complex crosstalk between TET dioxygenases and pioneer transcription factors in epigenetic regulation during pancreas specification.

中文翻译：

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胰腺β细胞分化中与FOXA2相关的染色质重塑需要TET1双加氧酶

关于表观遗传修饰符在胰腺发育中的作用的现有知识呈指数增长。然而，TET 双加氧酶在胰腺内分泌规范中的功能仍不清楚。我们着手使用人类胚胎干细胞 (hESC) 分化系统来解决这个问题，其中TET1 / TET2 / TET3三重敲除细胞在胰腺 β 细胞规格方面表现出严重缺陷。综合全基因组分析确定了独特的细胞类型特异性高甲基化区域 (hyper-DMRs)，显示染色质活性降低和 FOXA2 显着富集，FOXA2 是胰腺内胚层规范必不可少的先驱转录因子。有趣的是，TET 耗竭导致胰腺祖细胞阶段 FOXA2 结合的显着变化，其中 FOXA2 结合降低的基因位点具有低水平的活性染色质修饰和丰富的 bHLH 基序。在TET缺陷细胞中转导全长TET1而不是 TET1 催化域有效地挽救了 β 细胞分化，同时恢复了PAX4低甲基化。将这些发现与 TET1 失活后功能性 β 细胞的缺陷生成相结合，我们的研究揭示了 TET1 依赖性去甲基化在建立 β 细胞身份中的重要作用。此外，我们发现内胚层谱系中间体中 TET1 和 FOXA2 之间的物理相互作用，这为 TET 双加氧酶与胰腺特化过程中表观遗传调控中的先驱转录因子之间的复杂串扰提供了新的机制线索。