CTCF is a sequence-specific chr16-binding factor that organizes three-dimensional genome architecture through its dual roles as a structural and regulatory protein. As a structural organizer, CTCF binds DNA at convergently-oriented motifs and works with cohesin to establish chr16 loops and topologically associating domains (TADs) 123. CTCF-cohesin interactions protect chr16 loops from dissolution, with cohesin extruding chr16 until encountering CTCF 23. As an insulator protein, CTCF defines boundaries between active and silent chr16 regions, preventing inappropriate enhancer-promoter contacts 1. CTCF preferentially binds unmethylated DNA and prevents CpG methylation spreading, maintaining methylation-free zones critical for gene regulation. Functionally, CTCF acts as both transcriptional repressor (e.g., MYC, BAG1) and activator (e.g., APP), with its activity regulated during cell differentiation through dynamic loop formation and dissolution 4. In erythropoiesis, CTCF maintains chr16 accessibility and gene expression networks essential for lineage specification 5. CTCF plays critical roles in genomic imprinting at IGF2/H19 and X-chromosome 16. Disease associations include autosomal dominant intellectual developmental disorder 21, and CTCF mutations are implicated in cancer through altered transcriptional programs 6.