Cell Division and Mitotic Spindle Orientation
The positioning of the cell division axis is a critical feature ensuring normal embryo development as well as normal tissue growth and renewal. Cell shape as well as cell polarity had been shown to have a role in spindle orientation. Differentiating between the influence of cell shape geometry and that of cortical cues associated with cell polarity was a major challenge in dissecting the finer elements controlling spindle orientation.
Pioneering work by Michel Bornens and coworkers using adhesive micropatterns have allowed to identify major elements governing spindle orientation.
Influence of cell shape factor on orientation of cell division
When cells are plated on culture dishes, great variability can be observed in cell morphology and polarization and spindle orientation is randomized. By using ECM micropatterns, cell geometries can be controlled and cell behavior can be observed in response to a given cell shape. Axis of cell division were measured on the following fully adhesive micropatterns (Rectangle, Disk, Triangle) and show that cell division axis tends to occur in the longest axis of the cell, supporting the theory that cell shape and elongation plays a role in orienting spindle orientation.
(see Thery NCB 2005 to learn how images were analyzed to automatically extract the division axis angle and how the angular histogram was built)
Imposing cell shape but controlling cortical heterogeneity by reducing cell adhesion
On the L versus the full Triangle, while both patterns induce a triangular shaped cell, the orientation of the cell axis is more tightly distributed along the hypotenuse. Thus, the interphase cell shape is not the only factor controlling spindle orientation. Adhesion point distribution also has an active role in positioning the mitotic spindle.
Cell cycle progression on micro-patterns is highly reproducible Video-recording (every 3 min by phase contrast at 10X ) of control unsynchronized RPE1cells seeded on L-shaped micropatterns. All video-recordings were post-synchronized using the metaphase step to place them in register.
The adhesive micropatterns show remarkable control of the orientation of the cell division axis. An example given below shows that although the cell has a similar square shape on all of the three micropatterns (the [X], the [L°] and the [=]), the axis of cell division is tightly dependent on the underlying geometry. On the [X], cells divide equally in both diagonals, on the dotted [L°], cells divide only according to one diagonal and on the [=], cells divide along the vertical axis. On the [=], the orientation at 45 ° from the long cell axis in interphase shows the dominance of the spatial distribution of the ECM over the geometrical shape of the interphase cell.
Hertwig’s rule (1892) : “Cells divide along their long axis” Is not respected
Imposing cell shape, but disrupting cortical heterogeneity using drugs
Drugs disrupting the cortical organization of the cell also disrupt the orientation of the mitotic spindle.
Conclusion:
The distribution of the ECM and hence the cortical heterogeneity of the cell overrides the effect of cell shape and Hertwick’s long-standing “long axis” theory. Spindle orientation may be influenced by the cell shape anisotropy during cell rounding, but its final orientation is defined by the cortical marks that become associated with the retraction fibers (see Thery NCB 2005 for more on retraction fibers). Adhesive micropatterns are the only technology which has allowed to dissociate the influence of each factor and determine the precise chronology of events leading to predictive spindle orientation. This is directly relevant to what takes place in tissue and embryo development.
Click here to read more about:
- Quantitative analysis of cell cycle progression
- Controlling symmetric and asymmetric cell division orientation
- Controlling multipolar divisions in multi centrosome cells
|
The extracellular matrix guides the orientation of the cell division axis. |
|