Fig. 2. Dlx+ and GnRH+ neurons found in the nasal mesenchyme have a placodal origin. (A-C') Dlx3, Dlx5 and Pax6 in olfactory epithelium at HH19-20. Levels of Dlx3 are strong throughout the olfactory pit (A,A') and also in the otic pit (ot) and branchial arches. (B) Dlx5 is expressed in olfactory and otic placodes, broadly in branchial arches, in the neural crest-derived part of trigeminal ganglion (tg) and in ingressing olfactory placode cells (B', arrowhead). (C) Pax6 is expressed in olfactory pit, eye (e) and forebrain. (C') Section through olfactory placode. Broken black lines indicate planes of section. (D-f') Placodal origin of GnRH neurons. (D) Whole-mount view of HH18 embryo electroporated with pCIG-GFP at HH10. Broken black lines indicate transverse sections through the olfactory epithelium shown in d-d''. (d) Section through the olfactory pit. Arrows indicate multiple GFP+(green)/pan-Dlx+(red) cells. (d',d'') Sections through more basal regions of the olfactory system. Neurons (indicated by arrows, Hu+, blue) that ingress from the placode (GFP+,green) are also Dlx+. (E) Ventral whole-mount view of HH27 embryo electroporated with pCIG-GFP at HH10; inset shows schematic of ventral view of HH27 embryo, red box indicates area shown at high magnification. (e) Numerous GFP+ (green) cells are observed in a ganglion-like structure. Arrow indicates a GFP+ GnRH neuron (inset). (e') A nearby section has pan-Dlx+/GFP+ cells (arrows; insets). (f,f') Sections through a similar embryo. Arrows indicate GFP+/GnRH+ neurons (f) and GFP+/pan-Dlx+ neurons in an adjacent section (f'). Higher magnification views can be seen in insets. (G) Transverse section through the olfactory epithelium of a non-electroporated HH25 chick embryo. GnRH (red) Hu/neurofilament (green)-positive neurons (indicated by arrowheads) are seen within the olfactory epithelium and just ventral to it. oe, olfactory epithelium; m, maxillary epithelium; fb, forebrain; e, eye.