The human genome carries genetic information in two distinct forms: Transcribed genes and regulatory DNA elements (rDEs). rDEs control the magnitude and pattern of gene expression, and are indispensable for organismal development and cellular homeostasis. Nevertheless, while large-scale functional genetic screens greatly advanced our knowledge in studying mammalian genes, such tools to study rDEs were lacking, impeding scientific progress. Interestingly, recent advance in genome editing technologies has not only expanded the available screening toolbox to examine genes, but also opened up novel opportunities in studying rDEs. We distinguish two types of rDEs: Transcriptional rDEs that recruit transcription factors to enhancers, and structural rDEs that maintain chromatin 3D structure to insulate transcriptional activities, a feature postulated to be essential for gene expression regulation by enhancers. Recently, we developed a CRISPR strategy to target enhancers. We showed its scalability and effectivity in identifying potential oncogenic and tumour-suppressive enhancers. Here, we will exploit this line of research and develop novel strategies to target structural rDEs (e.g. insulators). By setting up functional genetic screens, we will identify key players in cell proliferation, differentiation, and survival, which are related to cancer development, metastasis induction, and acquired therapy resistance. We will validate key insulators and decipher underlying mechanisms of action that control phenotypes. In a parallel approach, we will analyse whole genome sequencing datasets of cancer to identify and characterize genetic aberrations occurring in the identified regions. Altogether, the outlined research plan forms a natural extension of our successful functional approaches to study gene regulation. Our results will setup the foundation to better understand principles of chromatin architecture in gene expression regulation in development and cancer.