Fig. 2. Forebrain marker gene expression is unaltered in Otx1l/2 hypomorphic (OtxH) embryos at early stages. Gene expression profile of OtxH embryos at 12 somites (15 hpf; A-F) and prim-15 (30 hpf; G-L). (A,C) pax6a and epha4a mark the forebrain anlage and demarcate at the diencephalic-mesencephalic boundary. (B,D) Although the hindbrain expression domains start to shift anteriorly (asterisks), the forebrain expression domains of these genes are unaltered in OtxH embryos at this stage. (G-J) At prim-15, in control siblings, pax6a and epha4a become downregulated in the mid-diencephalon (marked by arrowheads); this structure is not detectable in OtxH embryos (pax6a: 26/32; epha4a: 36/41). Compared with control siblings, the expression domains of pax6a and epha4a shrink in the anteroposterior direction. (E,F) barhl2 is expressed in the MDT at 12 ss (E) and its expression is indistinguishable from OtxH embryos at the same stage (F). (K) At prim-15, barhl2 marks the dorsal telencephalon and the MDT, including the ZLI (12/30). (L) In OtxH embryos, the ZLI expression is absent, whereas the dorsal telencephalic domain persists. con, control; dTel, dorsal telencephalon; DMB, diencephalic-mesencephalic boundary; FB, forebrain; HB, hindbrain; MB, midbrain; MDT, mid-diencephalic territory; prim-15, primordium stage 15; R1, rhombomere 1; R3, rhombomere 3; ss, somite stage.