Two photon micrograph of a 3D segmented whole mouse embryo (orange/blue) overlaid on a 2D greyscale differential interference contrast (DIC) micrograph. A live mouse embryo was visualised during preimplantation development, the time between fertilisation and implantation of the embryo into the mother's uterus (womb). Whole mouse embryos were digitally segmented and changes in each cell's shape and position over time was tracked in 4D. Here, one cell (orange) in the 8-cell embryo (neighbouring cells are blue) is in the process of moving from the surface to the inside of the embryo. This process of internalisation takes approximately 4-5 hours. The early mouse embryo is approximately 90 micrometres in diameter.
Mammalian embryos start out as a small group of identical cells. At an early stage, during the transition from 8 to 16 cells, some cells take up an internal position within the embryo. These internal cells will go on to form all of the cells in the body while the outer cells go on to form other tissues such as the placenta. The internal cell adopts its position in the embryo through a special process of cell division.
