Fig. 2. ERK and ELK1 are phosphorylated during mouse preimplantation development. (A) Phosphorylated ERK (p-ERK, upper) and phosphorylated ELK1 (p-ElK-1, lower) were detected using anti-phospho-ERK antibody and anti-phospho-ELK1 antibody, respectively. Embryos (from left to right) at the two-cell, four-cell, eight-cell, morula or blastocyst stages were fixed and stained. Fluorescence was viewed with a confocal microscope. (B) Phosphorylation of ERK or ELK1 with or without U0126. Four-cell (top) and two-cell (bottom) stage embryos were treated with U0126 for 1 hour, and then the embryos were fixed and stained with either anti-phospho-ERK antibody (four cell) or anti-phospho-ELK1 antibody (two cell). Fluorescence was viewed with a confocal microscope.