Immunostaining for HuC/D in the rostral hypothalamus of DMSO and DAPT-treated chick embryos (n = 6). (A,B) High magnification of hemisected, flatmounted preparations of the rostral hypothalamus at Hamburger and Hamilton (HH)13. The nucleus of the tract of the postoptic commissure neurons (nTPOC) was characterized by the expression of the Hu class of RNA-binding proteins that marks post-mitotic neurons. While the neurons were scattered in the DMSO control (A), after DAPT treatment the nTPOC population becomes denser (B). DMSO; DAPT, N-[3.5-difluorophenacetyl-L-alanyl)]-S-phenylglycine t-butyl ester.