Pax6 is essential for the establishment of the mid-diencephalon in zebrafish. (A-F) Whole mount double in situ hybridization (ISH) for indicated markers of 28 hours post-fertilization (hpf) zebrafish embryos of indicated experimental procedure. Double red arrows mark MDO thalamic primordial. In B, D and F, black dashed line marks the border between MDO and the prethalamus, and white dashed line marks the border between MDO and thalamus. (G) Schematic representation of a sagittal section of zebrafish forebrain at 28 hpf. cTh, caudal thalamus; ETh, epithalamus; MDO, mid-diencephalic organizer; PrT, pretectum; PTh, prethalamus; rTh, rostral thalamus; ZLI, zona limitans intrathalamica.