Activation of Tbx1-GFP in the inner ear using Tbx1Cre/+. (A) Immunofluorescence with GFP (red) and Tbx1 (red) antibodies on E10.5 transverse sections through the otic vesicle (OV). The VIIIth cranial ganglion, also known as the cochleovestibular ganglion (CVG) is adjacent to the OV. Neural tube (NT). (B) Activation of Tbx1-GFP by Tbx1Cre/+ does not produce major morphological defects of the inner ear, as visualized by paintfilling at E14.5. (C) Paintfilling shows failure of inner ear morphogenesis in Tbx1Cre/- null mice at E14.5 compared to the Tbx1-GFPflox/+ control. Activation of a single allele of Tbx1-GFP on a Tbx1Cre/- null background is capable of partially rescuing morphogenesis.