SOX2 hypomorphism disrupts development of the prechordal floor and optic cup

► We examine mouse embryos that are hypomorphic for the transcription factor SOX2. ► Sox2 hypomorphic embryos exhibit an abnormal prechordal floor and optic anlage. ► The prechordal floors of Sox2 hypomorphic embryos exhibit ectopic Shh signaling. ► Sox2 hypomorphic retinas exhibit disrupted ciliary vs. neural patterning. ► The observed phenotypes are consistent with those of SOX2 haploinsufficient humans.