Protrusion, Retraction and the Efficiency of Cell Locomotion

Abstract

Protrusion and retraction are two conspicuous aspects of the phenomenon of amoeboid locomotion or of the crawling motility of tissue cells. At the most general level, protrusion is the gain of territory that the cell makes during a short time interval and retraction is the loss of territory during the same interval. This territory may be considered to be the three-dimensional space occupied by the cell or, particularly if the cell is crawling over a planar substratum, it may be considered to be the two-dimensional projection onto the substratum of this occupied space or it may even be considered as the area of the substratum to which the cell is actually attached.