Mice lacking FoxL2 do not form levator (Müeller) smooth muscle at E18.5. Immunofluorescent staining clearly shows an α-SMA-positive stripe (green color) indicating the formation of muscle in FoxL2+/− (A,C) but not in the FoxL2−/− (B,D) mouse. Asterisks indicate α-SMA positive blood vessel. Nuclear counterstaining with DAPI is blue. UL, upper eyelid; LL, lower eyelid; Co, cornea; Le, lens; Re, retina.