SIX6 (SIX Homeobox 6 ) is a homeobox protein that is similar to the Drosophila 'sine oculis' gene product. SIX6 has been showed to be involved in eye development. Defects in this gene are a cause of isolated microphthalmia with cataract type 2 (MCOPCT2). Six6 lentivirus (TET-inducible, Puro) expresses human SIX6 under the control of the Tet responsive promoter, with puromycin as a selection marker.