midcell

Midcell is a term used in cell biology to denote the central region of a cell along its long axis, roughly equidistant from opposite poles. It serves as a reference point for symmetry and the planning of division events, and its exact location can shift during the cell cycle as chromosomes are replicated and segregated.

In bacteria, midcell is typically the site where the division septum forms. The Z-ring, composed of FtsZ and other proteins, assembles at midcell to initiate cytokinesis. Regulatory systems bias this process toward midcell; for example, the MinCDE system in many species prevents division at the poles, promoting septum formation near the center. Nucleoid occlusion also helps prevent division over the chromosome. When midcell localization is disrupted, cells may produce minicells or anucleate cells.

In eukaryotic cells, midcell often refers to the equatorial region during cytokinesis. The contractile actomyosin ring forms at the cell center to drive ingression of the cleavage furrow, while the spindle midzone and central spindle organize microtubules for chromosome segregation. In plant cells, a related central region guides the formation of the cell plate via the phragmoplast.

Midcell can be quantified in imaging studies by measuring the distance from the cell center to the ends, frequently expressed as a ratio to cell length. This concept is used in analyses of cell size control, polarity, and division plane placement. Related concepts include cell polarity, septum placement, and cytokinesis machinery.