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 (CMV, Puro) expresses human SIX3 under the control of the CMV promoter, with puromycin as a selection marker.