CTCF belongs to the zinc finger transcription factor family, and it recognizes unusually long and remarkably divergent DNA target sequences to influence expression of many various genes. The DNA-binding domain of CTCF is composed of 11 Zn fingers including 10 that are of C2H2 class, and 1 that is of C2HC class, and they are highly conserved between vertebrate species. CTCF functions as a repressor of the c-myc gene and as a regulator of lysozyme gene expression. In addition, CTCF associates with the essential activator domain in the promotor region of the amyloid beta-protein precursor (APP) gene to activate transcription of APP. Expression of CTCF up-regulates APP expression and thereby, enhances synapse formations between primary neurons during development. CTCF is ubiquitously expressed and localized to the nucleus. During terminal differentiation, CTCF is negatively regulated by differential phosphorylation and also by decreases in CTCF mRNA and protein expression.