Mapping of otx2 expression relative to markers of the MDT. Whole-mount double in situ-hybridised wild-type embryos are mounted with anterior to the left and dorsal up. The markers and stages are indicated. (A) wnt8b marks the pZLI territory and shares the same anterior border as otx2 at ten somites (14 hpf). (B) At the same stage, otx2 is expressed in the territory from the pZLI to the midbrain, whereas irx1b and otx2 are co-expressed in the presumptive thalamic area and anterior midbrain. (C,D) At 15 somites (16.5 hpf), shha expression is induced within the otx2-positive domain (C) and its anterior border coincides with the anterior expression border of otx2 at prim-15 (30 hpf; D). (D') A cross-section shows that the otx2 expression domain marks the ZLI and the thalamus whereas the ZLI is only shha positive. In the pretectum, otx2 is weakly expressed. (E,E') dlx2a marks the territory of the prethalamus and is anteriorly adjacent to the otx2 expression domain (E); the cross-section reveals the abutting expression domains (E'). (F,F') Similarly to the shha expression domain, the expression domain of dbx1a overlaps with that of otx2 at the anterior ZLI domain and at the thalamus. (G,G') At 30 hours, the expression domain of irx1b persists in the thalamus, whereas the ZLI domain is only otx2 positive. T-shaped brackets mark the plane of the section in the following picture. dTel, dorsal telencephalon; Mb, midbrain; MHB, midbrain-hindbrain boundary; prim-15, primordium stage 15; PTec, pretectum; PTh, prethalamus; pZLI, presumptive zona limitans intrathalamica; ss, somite stage; Th, thalamus; ZLI, zona limitans intrathalamica.
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