Hedgehog signaling is required for pituitary cell specification and regulates olfactory placode size. Reduced Hedgehog signal transduction increases lens and olfactory placode domains, while reducing pituitary placode specification. (A,B) pitx3 expression in wild-type embryos. (C) dlx3b expression in wild-type embryos. Eighty-nine percent of smoothened mutants (n=83) have ectopic and retina-associated lenses (D,G), 7% have distorted lens (E) and 4% have fused lens (F). In smoothened mutants, we observe normal pitx3 expression in anterior neural plate border ectoderm at bud stage (not shown), and in lens tissue at prim-5 stage (D-G). By contrast, head mesenchyme and branchial arches fail to express pitx3 and expression in ventral forebrain is reduced (D,G). (C,H) In 97 smoothened mutant embryos, 5% had larger olfactory placodes (H) than wild-type embryos (C). Although the olfactory placodes never fuse across the ventral midline, this phenotype correlates with the extended and fused lens placodes in smoothened mutants. (A,D-F) Frontal view, dorsal is upwards; (B,C,G,H) side views, anterior towards the left, dorsal towards the top. Scale bars: 100 μm
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