PRC2-mediated repression is essential to maintain identity and function of differentiated dopaminergic and serotonergic neurons [bulk RNA-Seq]

Neurons of the CNS must maintain their distinct identity over an entire lifespan. Apart from instructive information provided by transcription factors driving neuron specific genes, other gene programs need to be permanently silenced. The mechanisms governing enduring gene-silencing in neurons are largely unknown, as are the consequences if they fail. Here we show that loss of the Polycomb repressive complex 2 (PRC2) obligate unit Eed in differentiated murine midbrain dopamine (mDA) neurons resulted in progressive loss of the H3K27me3 histone modification followed by upregulation of PRC2 targets, also highly enriched for the constitutive heterochromatin H3K9me3 modification. This was followed by reduced expression of mDA neuron-identity genes, particularly evident in the Substantia nigra pars compacta. Consequently, mDA-neuronal function was severely disrupted, causing parkinsonian-like motor skill deficits. Deletion of Eed in differentiated serotonergic (5HT) neurons resulted in a similar upregulation of PRC2-targets and reduced expression of genes defining 5HT neurons, which promoted loss of serotonergic identity followed by loss of function and altered behaviour. Overall, our results reveal that PRC2 inactivation leads to a selective and progressive loss of mDA or 5HT neuronal identity and function, but not to any loss of cells. Thus, our study shows that PRC2-dependent maintenance of neuronal identity is essential and safeguards against expression of other non-relevant gene programs and loss of neuronal function. Evaluation of gene expression in dopaminergic and serotonergic neurons with and without functional Polycomb repressive complex 2 (PRC2).中枢神经系统（Central Nervous System, CNS）的神经元需在完整生命周期内维持其独特的细胞身份。除驱动神经元特异性基因表达的转录因子所提供的指导性信息外，其余基因程序需被永久沉默。调控神经元中长期基因沉默的机制在很大程度上仍未明确，其失效后引发的后果亦然。本研究显示，在分化成熟的小鼠中脑多巴胺（midbrain dopamine, mDA）神经元中敲除多梳抑制复合体2（Polycomb Repressive Complex 2, PRC2）的必需亚基Eed后，会导致H3K27me3组蛋白修饰逐步丢失，随后PRC2靶基因出现上调，且这些靶基因同时高度富集组成型异染色质H3K9me3修饰。随之而来的是mDA神经元身份相关基因的表达下调，该现象在黑质致密部（Substantia nigra pars compacta）中尤为显著。最终，mDA神经元的功能遭到严重破坏，引发帕金森样运动技能缺陷。在分化成熟的血清素能（serotonergic, 5HT）神经元中敲除Eed，则会出现类似的PRC2靶基因上调，以及编码5HT神经元特征基因的表达下调，进而促使血清素能神经元身份丢失，随后出现功能丧失与行为改变。综上，本研究结果表明，PRC2失活会选择性且逐步地导致mDA或5HT神经元的身份与功能丧失，但不会引发细胞丢失。由此可见，依赖PRC2的神经元身份维持机制至关重要，可防止其他非相关基因程序的异常表达，并避免神经元功能丧失。本数据集针对拥有或缺失功能性多梳抑制复合体2（Polycomb Repressive Complex 2, PRC2）的多巴胺能与血清素能神经元的基因表达情况展开了分析。