Repression of Irs2 by let-7 miRNAs is essential for the homeostasis of the telencephalic neuroepithelium [miRNA-seq]

The structural integrity and cellular homeostasis of the embryonic stem cell niche are critical for normal tissue development. In the telencephalic neuroepithelium, this is controlled in part by cell adhesion molecules and regulators of progenitor cell lineage, but the specific orchestration of these processes remains unknown. Here we have studied the role of microRNAs in the embryonic telencephalon as key regulators of gene expression. By using the early recombiner Rx-Cre mouse, we demonstrate that miRNAs are essential to preserve the cellular homeostasis and structural integrity of the telencephalic neuroepithelium. We show that Rx-Cre;Dicerflox/flox mouse embryos have a severe disruption of the telencephalic apical junction belt, followed by invagination of the ventricular surface and formation of hyperproliferative rosettes. Transcriptomic analyses and functional experiments in vivo show that these defects result from upregulation of Irs2 upon loss of let-7 miRNAs, in an apoptosis-independent manner. Our results reveal an unprecedented relevance of miRNAs in early forebrain development, with potential mechanistic implications in pediatric brain cancer. The rostral-most region of the telencephalic primordium was dissected out from DicerF/F and RxCre-DicerF/F E11.5 embryos, and miRNA expression profiles were analysed by RNA sequencing (RNA-seq).胚胎干细胞巢（embryonic stem cell niche）的结构完整性与细胞稳态，对正常组织发育至关重要。在端脑神经上皮（telencephalic neuroepithelium）中，该过程部分由细胞黏附分子与祖细胞谱系调控因子介导，但这些过程的具体协同调控机制仍不明晰。本研究聚焦于胚胎端脑中作为基因表达关键调控因子的微小RNA（microRNAs, miRNAs）的功能。借助早期重组酶Rx-Cre小鼠模型，我们证实miRNAs对于维持端脑神经上皮的细胞稳态与结构完整性不可或缺。研究发现，Rx-Cre;Dicerflox/flox小鼠胚胎出现端脑顶部连接带严重破坏，随后伴随脑室表面内陷以及过度增殖性神经玫瑰结（rosettes）的形成。转录组分析与体内功能实验表明，上述缺陷源于let-7 miRNAs缺失后胰岛素受体底物2（Irs2）的上调，且该过程不依赖细胞凋亡。本研究结果揭示了miRNAs在早期前脑发育中前所未有的重要性，其机制或可为儿童脑癌研究提供潜在参考。研究人员从DicerF/F与RxCre-DicerF/F品系的E11.5小鼠胚胎中分离出端脑原基的最吻侧区域，并通过RNA测序（RNA-seq）分析miRNA表达谱。