Regionalized expression of the components of the Notch pathway in the hypothalamus. Expression of Dll1, Hes5 and Hey1 at Hamburger and Hamilton (HH)11 and HH13 as indicated. All genes were detected initially as a crescent region between the two optic vesicles (boxes in A,E,I). (B,C,F,G,J,K) Double expression of Dll1, Hey1 or Hes5 (blue) with Nkx2.1 (red) at HH13, showing that the expression of all the genes occupies the rostral region of the hypothalamus. (C,G,K) Hemisected, flatmounted preparation of the ventral diencephalon of the corresponding embryos in B,F,J, respectively, with the optic vesicles removed and viewed from the ventral side. Arrowheads indicate scattered cell expression. Asterisk indicates rostral expression caudal to the prospective chiasmatic area. (D,L) HH10 chick embryos were treated with N-[3.5-difluorophenacetyl-L-alanyl)]-S-phenylglycine t-butyl ester (DAPT) or (DMSO) for 16 hours. (H) Embryos were treated for only 3 hours from HH12. There was downregulation of Hes5 (H) and Hey1 (L) expression after DAPT treatment, whereas Dll1 was upregulated (D). AH, anterior (rostral) hypothalamus; D, diencephalon; H, hypothalamus; pH, hypothalamus primordium; POA, preoptic area; T, telencephalon, V, optic vesicle.