Embryo (E) timing was based upon identification of coital plugs (equal to E0.5). Immunohistochemical methods were as described . Embryos were fixed in PBS/2% paraformaldehyde/5% sucrose, cryoprotected with sucrose in PBS to a final of 30%, embedded and sectioned using a Microm EM550 microtome. The 12-lm sections were mounted on glass slides, blocked, and permeabilized with 1% deoxycholate and 0.2% Triton X-100 in PBS, and then incubated overnight at 4°C with the appropriate primary antibodies. After washing, sections were incubated with secondary antibodies conjugated to fluorescent markers (Jackson Immuno-Research, West Grove, Pennsylvania) for 1 h at room temperature. The sections were again washed, and mounted in prolog gold antifade reagent (Invitrogen, Grand Island, New York; P36930) and cover-slipped before being photographed using fluorescence microscopy . Images were collected using a Microfire 24-bit CCD camera (Optronics, Goleta, California) and imported into Photoshop C2 for preparation of figures.