TREX复合体在histone mRNA 的3'端加工和出核中的功能机制研究

The highly conserved TREX complex (TREX) plays an important role in nuclear export of mRNAs containing polyA tail. Metazoan replication-dependent histone mRNAs (RD histone mRNAs) are the only eukaryotic mRNAs that lack a polyA tail, instead ending with a conserved stem loop structure. RD histone mRNAs encode histone proteins for packaging newly synthesized DNA in chromatin and plays key roles in many important biological processes, such as cell proliferation. The 3’ processing and nuclear export of RD histone mRNAs are tightly controlled, however, the underlying mechanism remains elusive. Our preliminary data demonstrate that ALYREF, a component of the TREX, specifically binds to a region upstream adjacent to stem loop on most RD histone mRNAs. Here, we plan to study how TREX is recruited to this specific region, investigate the function and mechanism of TREX in 3’ processing and nuclear export of RD histone mRNAs , reveal the mechanism for linking histone pre-mRNA processing to mRNA export. This study will reveal novel regulatory mechanisms for the expression of RD histone mRNA and provide important clues for understanding the physiological and pathological functions of TREX.

在真核细胞中，绝大多数的mRNA均具有polyA尾，其出核转运依赖高度保守的TREX复合体。复制依赖型的histone mRNA（RD histone mRNA）是唯一一类不具有polyA 尾的mRNA，其3’端由茎环结构代替，它编码的组蛋白在细胞增殖等重要生物学过程中发挥关键作用。RD histone mRNA的3'端加工和出核过程受到严格的调控，然而，其中的分子机制还不十分清楚。我们前期研究发现：TREX组分ALYREF广泛而特异地结合在RD histone mRNA的茎环区域。在本项目中，我们将研究此特异性结合的分子机制；探索TREX在RD histone mRNA 加工和出核过程中的功能和机制；探究RD histone mRNA 的3’端加工和出核间的偶联。此研究将揭示调控RD histone mRNA表达的新机制，并为理解TREX的生理病理功能提供重要线索。

复制依赖型的histone mRNA（RD histone mRNA）是唯一一类不具有polyA尾的mRNA，取而代之的是一个高度保守的茎环结构。它编码的组蛋白在核小体组装、细胞增殖等多种基本生命过程中发挥关键作用。RD histone mRNA的3’端加工需要茎环结合蛋白SLBP（stem loop binding protein）和U7 snRNP的共同参与。关于RD histone mRNA 3’端加工和出核的研究比较有限。在此项目中，通过对TREX组分ALYREF iCLIP数据的深入分析，我们发现ALYREF不仅结合polyA+ mRNA，而且广泛而特异地结合在RD histone mRNA的茎环结构区域，这种结合主要通过ALYREF与SLBP直接互作实现。ALYREF在histone mRNA的加工与出核过程中均发挥着重要作用：一方面ALYREF通过与U7 snRNP的核心组分Lsm11直接互作辅助其招募，从而促进pre-histone mRNA 的3’端加工；另一方面，ALYREF协同整个TREX复合体促进成熟histone mRNA的出核转运。更为重要的是，3’端加工能够显著促进ALYREF的招募和histone mRNA的出核。此工作揭示了ALYREF协同调控histone mRNA加工和出核的功能机制，扩展了对TREX功能的认知，推进了对组蛋白基因表达调控的理解。