A cleavage furrow is a temporary indentation that forms in the plasma membrane of an animal cell undergoing cell division. This structure marks the beginning of cytokinesis, the final stage where the cell physically divides into two separate daughter cells. The furrow’s formation ensures that each new cell receives a complete set of genetic material and cellular components.
How a Cleavage Furrow Forms
The formation of a cleavage furrow begins with the assembly of a specialized structure called the contractile ring, located just beneath the cell’s outer membrane. This ring is primarily composed of two types of protein filaments: actin filaments and myosin II motor proteins. Actin filaments are thin, flexible protein strands, while myosin II proteins are molecular motors capable of moving along these actin tracks. The contractile ring forms in the cell’s equatorial plane, which is the middle region where the two sets of chromosomes have separated during nuclear division.
Myosin II motors within the ring bind to and pull on the actin filaments, causing the ring to constrict. This action is similar to pulling a drawstring on a bag, gradually tightening and reducing the ring’s diameter. As the contractile ring tightens, it pulls the overlying plasma membrane inward, creating the visible indentation known as the cleavage furrow. This continuous inward pinching motion progressively deepens the furrow until it meets in the center, cleaving the parent cell into two distinct daughter cells.
Its Role in Cell Division
The primary function of the cleavage furrow is to facilitate cytokinesis, the physical separation of the cytoplasm and organelles into two daughter cells. Following chromosome segregation during mitosis, the cleavage furrow ensures that this genetic material is precisely partitioned. Each daughter cell receives a full complement of chromosomes, maintaining genetic stability.
Beyond genetic material, the cleavage furrow also distributes other cellular components, such as mitochondria, ribosomes, and endoplasmic reticulum, between the nascent cells. This equitable distribution supports the proper functioning and survival of the new cells. The precise and timely formation of the cleavage furrow is fundamental for successful cell reproduction, supporting maintenance of tissues and development of organisms.
Cleavage Furrow Variations
While cleavage furrows are a characteristic feature of animal cell division, their appearance and mechanisms can vary across different organisms and cell types. For instance, the timing and depth of furrow formation might vary depending on the cell’s size or the specific developmental stage. In some rapidly dividing embryonic cells, multiple furrows can form simultaneously or sequentially to facilitate quick cell divisions.
Cells with rigid cell walls, such as plant cells, do not form a cleavage furrow. Instead, they construct a new cell wall between daughter nuclei through the formation of a cell plate. This cell plate originates from vesicles that fuse in the center of the cell, expanding outwards to divide the cytoplasm. The presence or absence of a cell wall dictates the mechanism of cytoplasmic division.