Xenopus tadpoles express foxj1 in distinct regions of the developing CNS. Whole-mount in situ hybridization of staged embryos and explanted brains. (A) Expression at early neurula stage (dorsal (d) view). (B, C) Expression at late neurula stage in epidermis and floor plate, in dorsal (B) and frontal view (C). (D) Staining in the floor plate at stage 25. Note the higher expression level at the ampulla terminalis (arrowhead). (D ’, D” ) Transversal sections, levels indicated in (D), revealed staining in the ventral (v) midline (outlined arrowhead) (D’) and the zona limitans intrathalamica (ZLI; arrowheads) (D”). (E, F) Expression at stage 31 (E) and stage 36 (F) in the nephrostomes, the spinal cord, and the ampulla terminalis (arrowheads). (E ’, E ”, F ’, F” ) Histological sections as indicated in (E, F) highlighted expression in the rhombencephalic roof (arrowheads in E’, F’), the ventral midline (outlined arrowheads in E’, F’) as well as in the subcommissural organ (SCO; asterisk in E ”, F ”, G) and the ZLI (arrowheads in E ”, F” ). (G , H) Brain explants at stage 36 after in situ hybridization with antisense probes for foxj1 (G) and shh (H) in side view showed co-localization of mRNA expression in the ventral midline and the ZLI. a = anterior; arc = archencephalon; deu = deuterencephalon; l = left; mes = mesencephalon; p = posterior; pros = prosencephalon; rhomb = rhombencephalon; r = right; st. = stage.