Formation and consequences of cell patterns in preimplantation mouse development.

The behaviour of groups of cells was studied in culture during preimplantation mouse development. The following observations were made with intact embryos minus the zona pellucida and with embryos whose cells had been dissociated and recombined. The form of the 4-cell embryo was related to the behaviour of the first cell to divide to this stage. The form of the 8-cell embryo depended on contact between the groups of four cells each derived from a single cell at the 2-cell stage. The form of the 16-cell embryo depended on cell movement during and after division from the 8- to the 16-cell stage. These results suggest that the morphogenetic movements of these early embryonic cells are principally governed by continuous cell interactions after fertilization. The cell surfaces of the embryos were examined with scanning electron microscopy in an attempt to discriminate between the mechanisms which could account for these movements.