Cleavage furrow

In this electron micrograph of a cell, the cleavage furrow has nearly completely divided the cell.

Cilliate undergoing the last processes of binary fission, the cleavage furrow being clearly visible

In cell biology, the cleavage furrow is the indentation of the cell's surface that begins the process of cleavage, by which animal and some algal cells undergo cytokinesis. The same proteins responsible for muscle contraction, actin and myosin begin the process of forming the cleavage furrow. It is important to note that plant cells do not perform cytokinesis through this method.

Cleavage is caused by a ring of actin microfilaments known as the contractile ring, which forms under the cell's plasma membrane during early anaphase. Cleavage is driven by the motor proteins actin and myosin(the same proteins involved with muscle contraction). During cellular cleavage, the contractile ring tightens around the cytoplasm of the cell until the cytoplasm is pinched into two daughter cells.