Microinjector apparatus and experiment set-up. (A) The rail system maintains the alignment of the image plane of the ultrasound transducer (1) with the trajectory of the microinjector (2). The stage (3) on which the mouse is placed is adjusted to place the target region of the conceptus in the image plane by adjusting the position of the stage using the XYZ controls (4). The rail system increases efficiency by reducing time to target acquisition, improving accuracy and as a result contributes to improved overall survival. (B) The sharp bevelled tip of the microinjection pipette is shown. (C) A modified Petri dish containing PBS (5) is supported above the mouse using Plasticene blocks (6). A segment of the uterus is exposed through a small midline abdominal incision into the Petri dish. A thin transparent rubber membrane (7) attached to the under surface of the Petri dish (5) seals the dish to the dry denuded maternal skin (8), while a thicker silastic membrane (9) submerged within the Petri dish stabilizes the uterus during microinjection.