When reproductive biologists first looked at mouse eggs with the electron microscope, they saw a structure in the cytoplasm that they named "cytoplasmic lattices." In Scott Coonrod's laboratory at the Baker Institute, it was discovered that the lattices are formed with PAD6, one of the predominant proteins in the eggs.
PAD6 does not appear to play a role in the development of the egg itself. Therefore, mice unable to synthesize this protein may still carry normally developed eggs. However, if those eggs are fertilized, they do not develop beyond the two-cell stage. This is particularly interesting because the development of the mouse egg is under the control of the mother mouse's genome, but after fertilization, at the two-cell stage, the control shifts to the nucleus of the fertilized egg. The absence of PAD6 appears to disrupt this transition from maternal to embryonic control.
Because humans have this same protein in their eggs, it is hypothesized that PAD6 may play a role in human sterility.