Histone methylation mediated by NSD1 is required for the establishment and maintenance of neuronal identities [RNA-seq]

The formation of the mammalian neocortex during development requires coordinated establishment of functional regions at proper anterior-posterior and medial-lateral positions - area patterning, as well as neocortical layers. Although key transcription factors (TFs) were known to specify and maintain cell fates, mechanisms underlying how TFs are precise expressed and repressed are largely elusive. Here we showed that NSD1, the methyltransferase for histone H3 lysine 36 dimethylation (H3K36me2), controls both areal and layer identities of the neocortex. Nsd1-ablated neocortex showed prominent areal shift of all four primary functional regions and aberrant wiring of major cortico-thalamic-cortical projections. Nsd1 conditional knockout mice displayed defects in spatial memory, motor learning and coordination, reminiscent of patients with the Sotos syndrome carrying NSD1 mutations. Although projection neurons (PN) of neocortical layers were mostly properly produced and positioned upon Nsd1 deletion, post-mitotic PNs could not establish their layer-specific identities. More strikingly, in adult Nsd1 conditional knockout neocortices, superficial-layer PNs progressively mis-expressed markers for deep-layer PNs. Moreover, neocortical PNs ablated with Nsd1 remained immature morphologically and electrophysiologically. Loss of NSD1 in post-mitotic PNs causes genome-wide loss of H3K36me2 and re-distribution of DNA methylation, which accounts for diminished expression of neocortical layer specifiers but ectopic expression of non-neural genes. Our findings revealed that H3K36me2 mediated by NSD1 is required for establishment and maintenance of region- and layer-specific neocortical identities. Comparative gene expression profiling analysis of RNA-seq data for somatosensory cortices of 2.5 month old control and Nsd1Nex-cKO mice.发育过程中哺乳动物新皮层（mammalian neocortex）的形成，需要在正确的前后轴与内外轴位置协同建立功能区域——即区域模式化（area patterning），同时还需构建新皮层分层。尽管已知关键转录因子（transcription factors，TFs）可指定并维持细胞命运，但其调控转录因子精准表达与抑制的具体机制仍难以阐明。本研究发现，介导组蛋白H3赖氨酸36二甲基化（histone H3 lysine 36 dimethylation，H3K36me2）的甲基转移酶NSD1，可同时调控新皮层的区域与分层身份特征。 Nsd1基因敲除的新皮层呈现所有四个主要功能区域的显著区域偏移，且主要皮层-丘脑-皮层投射通路出现异常连接。Nsd1条件性敲除小鼠表现出空间记忆、运动学习与协调能力缺陷，这与携带NSD1突变的索托综合征（Sotos syndrome）患者的临床表型高度相似。 尽管Nsd1缺失后，新皮层分层的投射神经元（projection neurons，PN）大多能正常产生并定位，但有丝分裂后投射神经元无法建立其层特异性身份特征。更为显著的是，在成年Nsd1条件性敲除小鼠的新皮层中，浅层投射神经元会逐渐异常表达深层投射神经元的标志物。 此外，缺失Nsd1的新皮层投射神经元在形态与电生理层面均维持未成熟状态。有丝分裂后投射神经元中NSD1的缺失会导致全基因组范围内H3K36me2的丢失以及DNA甲基化的重新分布，这可解释新皮层分层特异性调控因子表达下调、而非神经基因异位表达的现象。 本研究结果揭示，由NSD1介导的H3K36me2对于区域与层特异性新皮层身份特征的建立与维持不可或缺。本研究对2.5月龄野生型对照与Nsd1Nex-cKO小鼠的躯体感觉皮层（somatosensory cortices）开展了RNA测序（RNA-seq）数据的比较基因表达谱分析。