Figure 4.

Midbrain specification under Otx2 temporal control. (A–T) In situ hybridization of sagittal sections of embryonic day (E)18.5 brains from Otx2^flox/CreERT2 embryos that received tamoxifen (Tam) at indicated times or solvent (Mock) with Gbx2 (A–E), Math1 (F–J), En1 (K–O) and TH (P–T). Rostral limit of Gbx2 expression is marked by black arrows. Ectopic Math1 expression is marked by red brackets. En1 labelling extension is indicated by black brackets. cb, cerebellum; ic, inferior colliculus; sc, superior colliculus. (U–Y) Alkaline phosphatase activity in sagittal sections of E18.5 Otx2^+/CreERT2 ; Z/AP animals that received tamoxifen at time corresponding to the panels above. Scale bar, 1 mm. (Z) Schematic representation of the temporal and spatial delineation (red bars) of the multiple requirements of Otx2 during the later stages of embryonic development.