Insulator function and CTCF

我们一直对蛋白质CTCF感兴趣，我们在几年前首次发现它具有绝缘体的特性，当它被放置在增强子和启动子之间时，它会阻止它们之间的相互作用。我们证明了这种活性在调节Igf2/H19印迹位点的亲本等位基因特异性基因表达中起重要作用。近年来，其他实验室的研究表明，CTCF的主要作用模式是招募内聚蛋白，从而稳定DNA上CTCF结合位点之间的相互作用，从而形成环域。根据相互作用的几何形状，这种环路可以排除导致绝缘的增强子，也可以使增强子和启动子靠得更近，从而导致激活。

We have been interested in the protein CTCF, which we first identified some years ago as having properties of an insulator, blocking interaction between enhancers and promoters when placed between them. We demonstrated that this activity plays an important role in regulating parent of origin allele-specific gene expression at the Igf2/H19 imprinted locus. Work in other laboratories in recent years has shown that a principal mode of action of CTCF is to recruit cohesin which in turn stabilizes interactions between CTCF binding sites on DNA, leading to formation of loop domains. Depending on the geometry of the interactions such loops can either exclude an enhancer leading to insulation, or bring enhancer and promoter closer together, leading to activation. DNA within the cell nucleus is packaged into chromatin, and further organized into topologically associated domains (TADs) separating active and inactive genomic regions. The establishment and maintenance of TADs requires the protein CTCF, and we are interested in identifying and studying the interactions of CTCF with the protein and nucleic acid partners recruited for insulator function. We have shown that the N- and C-terminal domains that flank the DNA binding 11 zinc fingers of CTCF appear to be intrinsically disordered explaining, in part, the large number of CTCF binding partners identified in other studies. Current work focuses on further characterizing the physical nature of these domains, identifying partners that bind with high affinity, and studying the complexes formed. We have participated in a collaboration investigating a possible role for SNPs affecting CTCF binding strength in expression of a gene associated with major mental illnesses. We have also begun a study of the organization of non-ribosomal genes within the nucleolus which is addressing both the genomic content and organization of the nucleolar genome. As part of our interest in large scale genome organization we have undertaken a study of the transcription factor MAZ, which is often bound at next to CTCF sites. We have observed interactions between the two proteins and an effect of MAZ on CTCF properties. As part of our interest in genome organization we have carried out a comparative study of the genomic content of nucleoli in multiple cell lines. This addresses the question of what non-ribosomal genes are present in nucleoli, with the goal of identifying the properties that determine that occupancy. Results show that there is a wide divergence of gene identity among cell types. All of these results relate to the role of chromatin structure, histone modifications, and long range organization of the genome in cell function, and are in turn related to questions of normal and abnormal cell metabolism and cell division.