Externally applied nucleus explantant orientates the locomotion of Amoeba proteus

The nucleus of Amoeba proteus acts on the cell cortex maintaining the activity and position of the frontal zone. Its effects are analogous to those of external stimuli. Both factors probably promote the separation of cell membrane from the underlying filamentous layer. In that way the hydrodynamic gradient that directs the cytoplasmic streaming and cell migration is created in the cell. Cessation of external stimulation does not disturb the cell locomotion, because the nucleus still maintains the necessary configuration of the frontal cortex. Reciprocally, the removal of the nucleus does not immobilize the cell, provided a strong enough external motor stimulus is acting. Only when both factors are removed or when the remaining single factor is too weak, the amoeba becomes incapable of locomotion. The cell nucleus and external stimulus to some extent replace each other, but an externally applied nucleus can be effective only in concert with the internal one. It seems, therefore, that the nuclear motor factor is rather weak, probably sufficient for maintaining the existing locomotory polarity but not for creating a new one. One can suppose, consequently, that the presence of the nucleus in the amoeba cell enables it to react to weak stimuli and persevere the orientated movement.