An eIF4E1/4E-T complex determines the genesis of neurons from precursors by translationally repressing a proneurogenic transcription program

Here, we have addressed the mechanisms that determine genesis of the correct numbers of neurons during development, focusing upon the embryonic cortex. We identify in neural precursors a repressive complex involving eIF4E1 and its binding partner 4E-T that coordinately represses translation of proteins that determine neurogenesis. This eIF4E1/4E-T complex is present in granules with the processing body proteins Lsm1 and Rck, and disruption of this complex causes premature and enhanced neurogenesis and neural precursor depletion. Analysis of the 4E-T complex shows that it is highly enriched in mRNAs encoding transcription factors and differentiation-related proteins. These include the proneurogenic bHLH mRNAs, which colocalize with 4E-T in granules, and whose protein products are aberrantly upregulated following knockdown of eIF4E, 4E-T, or processing body proteins. Thus, neural precursors are transcriptionally primed to generate neurons, but an eIF4E/4E-T complex sequesters and represses translation of proneurogenic proteins to determine appropriate neurogenesis. We obtained 3 biological replicates of IgG-bound RNA, 4E-T-bound RNA, and corresponding total RNA input from mouse E12-13 cortices. RNA samples were analyzed on the Affymetrix Mouse Gene 2.0 ST Arrays.本研究聚焦胚胎大脑皮层，阐明了发育过程中调控神经元精准数量生成的核心机制。我们在神经前体细胞中鉴定得到一种由eIF4E1及其结合蛋白4E-T组成的抑制复合物，该复合物可协同抑制调控神经发生相关蛋白的翻译。该eIF4E1/4E-T复合物与加工小体（processing body）蛋白Lsm1、Rck共同定位于颗粒结构中；此复合物的功能破坏会引发神经发生提前且增强，并导致神经前体细胞耗竭。对4E-T复合物的靶标分析显示，其高度富集于编码转录因子与分化相关蛋白的mRNA中，其中包括促神经发生的bHLH家族mRNA——这类mRNA与4E-T共定位于颗粒结构中，且在eIF4E、4E-T或加工小体蛋白被敲低后，其编码的蛋白产物会出现异常上调。由此可见，神经前体细胞在转录层面已具备生成神经元的潜能，但eIF4E/4E-T复合物通过隔离并抑制促神经发生蛋白的翻译，从而调控神经发生的正常进程。我们从小鼠E12-13胎龄皮层样本中，分别获取了IgG结合RNA、4E-T结合RNA以及对应的总RNA输入样本，共设置3次生物学重复。所有RNA样本均通过Affymetrix小鼠基因2.0 ST芯片阵列进行检测分析。