Multi-layered Control of the Exit from Stemness

促进正常神经干细胞退出干基的机制可能也可以驱动大脑 肿瘤干细胞分化。因此，对退出茎的控制的洞察将改善我们的 了解正常的神经发生和脑肿瘤的发展。从干性、神经性中退出 干细胞后代必须在mRNAs和蛋白质水平同步终止自我更新基因的活性。 虽然在理解自我更新基因的终止方面取得了巨大的进展 转录在离开茎的过程中，人们对转录后调控机制知之甚少 终止自我更新基因活性的机制。重要的是，关于如何区分控制，我们一无所知 各层协同作用终止所有水平的自我更新基因活性。通过使用苍蝇II型神经 作为一种范式，我们证明了转录、翻译和翻译后 作为同步终止自我更新的集成基因调控系统的一部分的控制功能 干细胞后代中所有水平的基因活性。在本提案中，我们重点关注翻译和后翻译 自我更新基因活性的翻译调控。我们证明了与RNA结合的蛋白质复合体 活跃在干细胞后代中通过结合独特的序列加速自我更新基因转录本的衰退 在他们的3‘UTRs中，并同时招募多个死烯基酶。此外，我们还展示了组合后的 多泛素E3连接酶复合体对蛋白质的快速截留和蛋白质降解作用 强健地终止自我更新蛋白质的活性。从“开”状态到“关”状态的稳健转换也是 许多控制发育信号机制的精确时空活动所必需的 图案化、增殖和细胞命运规范。对我们提出的集成基因调控系统的见解 将广泛适用于控制所有干细胞谱系中的退出干细胞以及 在正常发育过程中调节许多细胞命运的决定。

The mechanisms promoting the exit from stemness in normal neural stem cells likely can also drive brain tumor stem cells to differentiate. Thus, insights into control of the exit from stemness will improve our understanding of normal neurogenesis as well as brain tumor development. To exit from stemness, neural stem cell progeny must synchronously terminate self-renewal gene activity at the level of mRNAs and proteins. While tremandous progress has been made toward understanding the termination of self-renewal gene transcription during the exit from stemness, little is known about how post-transcriptional regulatory mechanisms terminate self-renewal gene activity. Importantly, nothing is known about how distinct control layers function synergistically to terminate self-renewal gene activity at all levels. By using the fly type II neural stem cell lineage as a paradigm, we demonstrated that transcriptional, translational and post-translational control function as part of an integrated gene regulation system that synchronously terminates self-renewal gene activity at all levels in the stem cell progeny. In this proposal, we focus on translational and post- translational control of self-renewal gene activity. We showed that RNA-binding protein complexes that are active in the stem cell progeny expedite self-renewal gene transcripts for decay by binding unique sequences in their 3'UTRs and recruiting multiple deadenylase concurrently. In addition, we showed that the combined effect of protein sequestration and proteolysis directed by multiple ubiquitin E3 ligase complexes rapidly and robustly terminates self-renewal protein activity. A robust transition from an “ON” to an “OFF” state is also required for precise spatiotemporal activity of many developmental signaling mechanisms that control patterning, proliferation and cell fate specification. Insights into our proposed integrated gene regulation system will be broadly applicable to the control of the exit from stemness in all stem cell lineages as well as the regulation of numerous cell fate decisions during normal development.