CACTIN is a conserved protein, discovered as a novel interactor of Drosophila IkappaB protein Cactus. It is highly conserved during evolution and plays a key role in early embryonic development. It is characterized as a negative regulator of many different developmental processes, but only found to play an immune role in humans. CACTIN localizes to nuclear speckles and colocalizes with known splicing proteins. It binds to a putative component of the spliceosome, major role for CACTIN in splicing.