Reporter transgene expression during midgestation. (A) Widefield fluorescent image of an E10.5 embryo. (B) Restricted GFP expression in the AER. Bright expression is detected in individual cells in the hindbrain (C), the otic vesicle (D), the foregut endoderm (E), the lining of the mesonephric duct (F, G) and the tailbud. Widefield fluorescent image of an E12.5 embryo (I) and close-ups of the ear (J) and limb (K). Transverse sections at E12.5 reveal transgene expression in the hindbrain (L), the infundibulum (M), the olfactory epithelium (N), the otic vesicle (O), oral ectoderm (P), spinal cord (R), heart (S), limbs (T), lung epithelia (U). fg, foregut; h, heart; hb, hindbrain; li, limb; lu, lung; ne, nasal epithelium; nph, mesonephric duct; nt, neural tube; ov, otic vesicle; RP, Rathke's pouch; tb, tail bud.