Figure 1.

The knock-in-based CreER^T2 strategy. (A) The mating of an Otx2^flox/CreERT2 male with a homozygous Otx2^flox/flox female yields 50% Otx2^flox/CreERT2 and 50% Otx2^flox/flox embryos. Intraperitoneal tamoxifen injection (Tam i.p., blue) triggers gene deletion only in Otx2^flox/CreERT2 embryos and solely in cells expressing Otx2. Purple and yellow boxes correspond to Otx2 and CreER^T2 genes, respectively, and red triangles to loxP sites. (B) Potentialities of the method. During normal development (top), two spatially and temporally distinct Otx2 expression sites (purple circles 1 and 2) control the development of structures S1 and S2. Depending on when CreER^T2 is activated (+tam, yellow stripes), the Otx2 gene is deleted in region 1 (middle) or 2 (bottom), perturbing development of structure S1 or S2, respectively. (C) In situ hybridization of Otx2^+/CreERT2 embryos at embryonic day (E)6.5–E10.5 (whole mount) and E16.5 (sagittal sections) and adults (transversal sections) at the level of mesencephalon (top) and cerebellum (bottom) with CreER^T2 and Otx2 probes (insets; for probes used, see supplementary Figs S1,S2 online). The arrow points to the isthmus. Scale bars, 100 μm for E6.5–E8.5, 500 μm for E10.5, E.16.5 and adult. cb, cerebellum; cp, choroid plexus; di, diencephalon; mes, mesencephalon; oe, olfactory epithelium; op, otic placode; ov, optic vesicle; sc, superior colliculi; tel, telencephalon.