Determining the Plane of Cell Division

A dividing cell accurately determining its plane of cell division is essential for the successful separation of chromosomes and the distribution of cytoplasmic contents to its daughter cells.

In animals, the division plane is located at the cell equator in between the segregated chromosomes, and its location is determined during anaphase. Microtubules that form the mitotic spindle interact with the cell cortex and play a decisive role in specifying the cleavage furrow.

Three different models are used to explain the determination of the cell division plane – the astral stimulation model, the polar relaxation model and the central spindle stimulation model.

In the astral stimulation model, radial arrays of astral microtubules interact with the equatorial cortex and induce the formation of the cleavage furrow.

In the polar relaxation model, astral microtubules send inhibitory signals to the cell poles and thereby suppress the formation of the cleavage furrow at both poles. This leads to cortical contraction at the cell equator.

Once the anaphase starts, the interpolar microtubules present between the segregated chromosomes rearrange into the overlapping antiparallel microtubules, also known as the central spindle. In the central spindle stimulation model, the central spindle stimulates the cleavage furrow formation at the equatorial cortex. 

The general consensus is that all three processes act together to determine the plane of cell division. This multi pronged approach can make the system respond to fluctuations in protein concentration as well as cell size and thereby increases the accuracy of cell division.

The contribution of each method depends upon the cell type and size. For example, in C. elegans embryos, a large array of astral microtubules is present and thus may play a more active role in the determination of the cell division plane.