Amino-terminal enhancer of split (AES) is a member of the groucho/TLE family of proteins. AES can function as a homooligomer or as a heteroologimer with other family members in order to forcefully repress the expression of other family member genes. Furthermore, AES can repress NFkB-regulated gene expression and is believed to have a significant role in initiating and maintaining cell differentiation events. AES is similar in sequence to the amino terminus of Drosophila enhancer of split groucho, a protein which is involved in neurogenesis during embryonic development. The AES protein is expressed predominately in the fetal brain, liver, lung, heart and kidney and also in the adult muscle.