Shh is required for pituitary induction, growth, and patterning. (A–C) shh is expressed adjacent to the pituitary anlage. (A) At 22 hpf, lateral view, showing shh (blue) in the hypothalamus (hyp), and lim3 (red) in the primordium of the adenohypophysis (pit). (B) At 26 hpf, frontal view, showing shh (red) in the hypothalamus (hyp), and prl in lactotropes (blue). Note that shh expression is strongest in the midline, adjacent to prl-negative medial cells of the pituitary placode. (C) At 45 hpf, lateral view, showing shh (blue) in hypothalamus (hyp), oral ectoderm (oe), and foregut (fg), and pomc in corticotropes and hypothalamic neurons (red). (D–J) shh is involved in pituitary induction and/or pituitary growth; (D–F) prl (blue) and lim3 (red), 26 hpf, frontal view, (D) control; (E) shh mRNA-injected embryo, with many extra prl- and lim3-positive cells in lateral placodal regions; (F) syu mutant, with reduced number of prl-positive cells (two cells indicated by arrows). (G, H) lim3 (blue), 22 hpf, frontal view; (G) control; (H) syu mutant, with moderately reduced number of lim3-positive cells, suggesting that pituitary induction is only slightly impaired. (I, J) prl (blue) and lim3 (red), 32 hpf, lateral view; (I) control; (J) syu mutant. The mutant pituitary is significantly thinner along its dorsoventral axis, with fewer prl- and lim3-positive cells (indicated in I, J by arrowheads and arrows, respectively), pointing to reduced proliferation and/or maintenance of pituitary cells. (K–N) syu mutants display defective pituitary patterning. (K, L) prl (blue) and pomc (red), 72 hpf, ventral view; (K) control; (L) syu mutant, with reduced numbers of lactotropes and corticotropes. (M, N) gh (blue); 72 hpf, ventral view; (M) control; (N) syu mutant, lacking somatotropes.
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