A mitotic intercellular bridge is a temporary, tube-like connection that forms between two newly divided daughter cells. This transient structure represents the final physical link before the cells fully separate from each other. It is a highly organized cellular component, playing a part in the successful conclusion of the division process.
The Final Act of Cell Division
Cell division culminates in a stage called cytokinesis. During cytokinesis, the cytoplasm of a single parent cell divides to form two distinct daughter cells. This physical separation follows the earlier stages of nuclear division, where duplicated genetic material is precisely distributed to each prospective daughter cell.
In animal cells, cytokinesis begins with the formation of a cleavage furrow, an indentation on the cell surface. This furrow deepens as a contractile ring, made primarily of actin and myosin filaments, tightens around the cell’s equator. The tightening ring effectively pinches the cell into two, and it is within this separating region that the mitotic intercellular bridge becomes visible.
How the Bridge Forms and What It Looks Like
The mitotic intercellular bridge presents as a narrow, membrane-bound tube connecting the two nascent daughter cells. This structure typically measures about 1 to 3 micrometers in diameter and can extend for several micrometers in length. Its formation is an event during the final stages of cytokinesis.
At the core of this bridge is a dense structure known as the midbody. The midbody is composed of tightly packed, antiparallel microtubules, which are remnants of the cell’s central spindle that helped separate chromosomes. Around these microtubules, the bridge also contains residual proteins from the contractile ring, such as actin and myosin, along with other specialized proteins that organize this temporary connection.
The Bridge’s Roles
The primary function of the mitotic intercellular bridge is to facilitate abscission, the final severing of the connection between daughter cells. While mitosis itself can be completed, the intercellular bridge can persist for minutes to several hours, depending on the cell type.
During this period, it can enable communication and the exchange of various cellular components between the connected cells. This exchange can include small molecules, signaling factors, and even vesicles or organelles.
What Happens When the Bridge Fails
Errors in the formation or resolution of the mitotic intercellular bridge can have serious consequences. If abscission fails, the daughter cells may remain persistently connected, or they might fuse back together. Such failures can lead to cells having an abnormal number of chromosomes, a condition known as aneuploidy.
Additionally, if chromosomes do not properly segregate during division, they can form chromatin bridges that physically link the separating nuclei. These chromosome bridges can interfere with the normal abscission process, leading to a delay or failure in cell separation. Improper bridge resolution or the presence of persistent bridges has been associated with the development of diseases, including various forms of cancer.