SIX3 (SIX Homeobox 3) is a member of the sine oculis homeobox transcription factor family and plays a role in eye development. Mutations in SIX3 have been associated with holoprosencephaly type 2. SIX3 lentivirus ((TET-inducible, Puro) expresses human SIX3 under the control of the Tet responsive promoter, with puromycin as a selection marker.