Fig. 4. Establishing the oocyte expression system. (A) Expression of GFP in Xenopus oocytes. Oocytes were injected with cRNA for GFP (1), or with water (2). Left, cells under normal light; right, fluorescence microscopy. (B) Expression of receptor XB107 in Xenopus oocytes. Oocytes were injected with an expression vector encoding receptor XB107 with an N-terminal Flag-Tag (lane 1) or water (lane 2) and incubated at 18°C for 7 days. The oocyte proteins were subjected to western blot analysis. The positions of molecular mass marker proteins are shown.