The Crosstalk of the Methyl-Cytosine Dioxygenase TET3 and the Methyl-CpG-binding protein MECP2 Controls Neuronal Maturation

Abstract Active DNA demethylation depends on Ten-Eleven-Translocation (TET) enzymes, which oxidize 5-methylcytosine (mC) to 5-hydroxymethylcytosine (hmC) and further derivatives. TET3, the predominant neuronal isoform, is mutated in the neurodevelopmental disorder Beck-Fahrner syndrome. Using human iPSC-derived neurons, we show that TET3 is dispensable for neuronal specification but critical for subsequent maturation. TET3-deficient neurons exhibit delayed transcriptional and proteomic transitions, altered synaptic signatures, and impaired network activity, indicating delayed functional maturation. Mechanistically, we identified an interaction between TET3 and the mC/hmC-binding protein MECP2, pathogenic variants of which cause Rett syndrome. MECP2 negatively regulates TET3 activity, as demonstrated in functional assays and by inverse hmC patterns in MECP2- and TET3-deficient neurons. Despite this, MECP2- and TET3-deficient neurons exhibit highly similar phenotypes at later differentiation stages. Our findings uncover a functional interplay between TET3 and MECP2 that coordinates DNA methylation and chromatin dynamics during neuronal maturation, suggesting a shared pathogenic mechanism in Beck-Fahrner and Rett syndromes.摘要 活性DNA去甲基化依赖于十-十一易位（Ten-Eleven-Translocation, TET）酶家族，该家族酶可将5-甲基胞嘧啶（5-methylcytosine, mC）氧化为5-羟甲基胞嘧啶（5-hydroxymethylcytosine, hmC）及其后续氧化衍生物。TET3作为神经系统中主要的神经元亚型，其突变可导致神经发育障碍性疾病贝克-法纳综合征（Beck-Fahrner syndrome）。本研究利用人诱导多能干细胞（induced pluripotent stem cell, iPSC）分化而来的神经元模型，证实TET3并非神经元命运特化所必需，但对神经元后续的成熟过程至关重要。TET3缺陷型神经元会出现转录组与蛋白质组转化延迟、突触特征异常以及神经网络活性受损等表型，提示其功能成熟过程出现延缓。从机制层面而言，本研究发现TET3可与mC/hmC结合蛋白MECP2发生相互作用，而MECP2的致病性变异可导致雷特综合征（Rett syndrome）。功能实验以及MECP2缺陷与TET3缺陷神经元中hmC分布呈反向变化的结果均证实，MECP2可负向调控TET3的酶活性。尽管存在上述调控关系，MECP2缺陷与TET3缺陷神经元在分化后期却表现出高度相似的表型特征。本研究结果揭示了TET3与MECP2之间的功能性互作关系，该互作可在神经元成熟过程中协同调控DNA甲基化与染色质动态变化，提示贝克-法纳综合征与雷特综合征存在共同的致病机制。