RT Journal Article SR Electronic T1 A CRISPR Screen Identifies Myc-associated Zinc Finger Protein (MAZ) as an Insulator Functioning at CTCF boundaries in Hox Clusters JF bioRxiv FD Cold Spring Harbor Laboratory SP 2020.08.25.267237 DO 10.1101/2020.08.25.267237 A1 Havva Ortabozkoyun-Kara A1 Pin-Yao Huang A1 Hyunwoo Cho A1 Varun Narendra A1 Gary Leroy A1 Jane A. Skok A1 Aristotelis Tsirigos A1 Esteban O. Mazzoni A1 Danny Reinberg YR 2020 UL http://biorxiv.org/content/early/2020/08/26/2020.08.25.267237.abstract AB The essential CCCTC-binding factor (CTCF) is critical to three-dimensional (3D) genome organization. CTCF binding insulates active and repressed genes within the Hox clusters upon differentiation, but such binding does not participate in boundary formation in all cell types, such as embryonic stem cells. We conducted a genome-wide CRISPR knockout screen to identify genes required for CTCF boundary activity at the HoxA cluster, complemented by novel biochemical approaches. This screen identified Myc-associated zinc finger protein (MAZ) as a CTCF insulator co-factor, among other candidates listed herein. MAZ depletion or specific deletion of MAZ motifs within the Hox clusters led to de-repression of posterior Hox genes immediately after CTCF boundaries upon differentiation, which phenocopied deletion of the proximal CTCF motifs. Similar to CTCF, MAZ interacted with the cohesin subunit, RAD21. Upon loss of MAZ, local contacts within topologically associated domains (TADs) were disrupted, as evidenced by HiC analysis. Thus, MAZ is a novel factor sharing insulation properties with CTCF and contributing to the genomic architectural organization.One Sentence Summary MAZ is identified as an insulator functioning at CTCF boundaries delimiting active and repressed genes at Hox clustersCompeting Interest StatementD.R. was a cofounder of Constellation Pharmaceuticals and Fulcrum Therapeutics. Currently, D.R has no affiliation with either company. The authors declare that they have no other competing interests.