Overexpression of fezl expands the telencephalon and hypothalamus at the expense of other fore- and mid-brain regions. (A-D) Expansion of telencephalic foxg1 (B) and hypothalamic nk2.1a (D), as compared with wild type (A,C). Arrow in A,B indicates foxg1-expressing cells; arrowhead in C indicates posterior boundary of nk2.1a-expressing cells. (E,F) Expansion of the optic stalk (os), reduction of the eyes and loss of MHB in fezl-overexpressing embryos (F) compared with wild-type (E). Inset in F shows another embryo of the same genotype as that shown in F, with a less-dramatic expansion of optic stalk but missing pax2a-expressing midbrain cells. (G-J) Loss of caudal diencephalic and midbrain irx3a (H) and MHB eng2 (J) expression in fezl-overexpressing embryos. Arrowhead in G,H indicates the mid-hind-brain boundary. All are lateral views of embryonic brain regions labeled with various region-specific markers. Stages and marker identities are specified in each panel. hy, hypothalamus; mhb, mid-hind-brain boundary; tel, telencephalon; os, optic stalk; e, eye region; tc, tectum; hb, hindbrain; pd, posterior diencephalon; tg, tegmentum.
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