Dynamics of Otx2-GFP expression at mid-gestation. Direct visualisation of GFP fluorescence of Otx2+/OGembryos and one control Otx2+/+E11.5 embryo (a-d) versus Otx2 mRNA localisation detected by whole-mount in situ hybridization on Otx2+/+animals (e-h) at indicated stages. Anterior is leftward. The arrow indicates the position of the midbrain-hindbrain boundary. Lower right panels: direct detection of GFP fluorescence of transverse sections of E12.5 Otx2+/OGembryo at the level of nasal cavities (i), eyecup (j) and inner ear (k). di, diencephalon; mes, mesencephalon; oe, olfactory epithelium; ov, optic vesicle; tel, telencephalon. Scale bars: 500 μm in a-d, 100 μm in i-l.