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Fig. 4 Overexpression of fezl results in an expansion of the prethalamus and the elimination of the ZLI in a dose-dependent fashion. The hsp-gal4 transgenic fish are crossed with uas-fezl transgenic fish and embryos are heat shocked at 37°C for 15-45 minutes at ~75% epiboly. Embryos are stained with indicated probes and analyzed at 28 hpf. Genotypes are identified by PCR with DNA from the tail. (A-D) The expression of dlx2a in the prethalamus is mostdramatically expanded. Its expression in the ventral telencephalon is mildly increased whereas its expression in the pharyngeal arches (pa) is not significantly altered. Arrow in A-D indicates dlx2a-expressing hypothalamic cells; black arrowheads in A-D indicate the pharyngeal arches; gray arrowhead in B-D indicates ectopic dlx2a-expressing cells in the midbrain. (E-H) The ZLI, as shown with shh expression, is moved caudally or completely eliminated depending on the duration of heat shock, but shh expression in the floor plate (fp) is unaffected. Square brackets indicate the ZLI. All are lateral views. hy, hypothalamus; pt, prethalamus; tel, telencephalon; fp, floor plate; bp, basal plate; pa, pharyngeal arches.