肿瘤相关蛋白核糖核酸酶-4（RNASE4）和血管生成素（ANG）均为核糖核酸酶A超家族成员，其基因前后排列在同一基因座上，共享启动子和非编码外显子，是人类基因组中一种非常罕见的基因组织方式。生物信息学分析显示，这两个基因在一些组织中存在着差异表达，但其调控机制未明。我们发现，ANG和RNASE4基因座上存在着一个由转录因子CTCF介导的基因内染色质环结构；过表达CTCF导致ANG表达水平显著提高，而RNASE4没有明显变化。在以上工作基础上，本项目拟进一步利用Reverse ChIP、ChIP-loop、3-C等技术，明确CTCF介导该特殊染色质环形成的具体机制；然后，利用CRISPR/CAS9基因编辑等技术，探索该染色质环在ANG和RNASE4基因差异表达中的作用；最后，在人体组织中验证以上发现。我们认为，该项目研究可能揭示生物体内基因表达调控的一种新机制。

Ribonuclease 4 (RNASE4) and angiogenin (ANG), two tumor-associated proteins, belong to the ribonuclease A superfamily. The locus encoding these two genes has a unique gene arrangement in whole human genome, in which the two genes share the same promoters and untranslated exons followed by two distinct exons encoding the two proteins, respectively. The bioinformatic analysis of gene expression data revealed that ANG and RNASE4 are differentially expressed in several tissues, but the mechanism of gene regulation is unknown. Our previous results showed that the CCCTC-binding factor (CTCF) formed a chromatin loop between the two introns flanking the ANG coding exon; overexpression of CTCF results in transcription increasing of ANG but not RNASE4. Based on the above work, this project aims to elucidate the mechanism by which the CTCF forms a chromatin loop in this gene locus using ChIP, ChIP-loop, 3-C et al.; next, we will explore the effects of this chromatin loop on differential gene expression through CRISPR/CAS9 gene editing technology. Finally, we will verify the above finding in human tissue. In our view, this project may reveal a new mechanism of gene regulation in the cell.