opl and fkh5 are expressed in adjacent domains that mark presumptive telencephalon and diencephalon at gastrula. Staged embryos were stained for opl RNA (orange) and fkh5 RNA (purple) using whole-mount in situ hybridization. (A) Mid-gastrula (75% epiboly) embryo, dorsal view, dotted line marks blastoderm margin; dashed line outlines anterior neural plate. (B) Late gastrula (90% epiboly) embryo, dorsal view; ad, anterior domain of fkh5 expression; pd, posterior domain of fkh5 expression. (C) Early neurula (tailbud) embryo, dorsal view, arrow shows plane of section shown in D. (D) Transverse section through a tailbud stage embryo. Note that staining is strong in the epiblast (e) and excluded from hypoblast (h). (E) Early somitogenesis (5 somite) embryo, side view. (F) Late somitogenesis (prim-5) embryo, side view, asterisks indicate weak fkh5 staining. a, anterior; t, telencephalon; d, diencephalon; m, mesencephalon; p, posterior; r, rhombencephalon; s, spinal cord.
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