The basic stages of cell division (mitosis) can be seen live under a microscope and we now have a detailed overall description of the process. However, our understanding of the mechanisms involved in cell division is incomplete. In particular, there is no explanation for how the overall geometry is determined.
During the first stages of mitosis, the centrosomes (Fig. 1) are the regions of the cell that start the formation of filaments (microtubules) that later arrange into the mitotic spindle. The spindle consists of two parts – half-spindles. Each microtubule runs from one centrosome to the middle of the spindle, overlapping with microtubules of the other half-spindle.
The identification of mitosis with liquid crystalline (LC) phases is an old idea. It was pointed out that naturally occurring liquid crystals (LC’s) are intimately connected with life processes. Bernal went further and suggested that the living cell is actually a LC. This view has since been repeated, but no attempt has been made to propose a detailed theory. In this work, we use a mathematical model of a nematic LC for the cytoplasm of the cell and show that the geometry of the prophase and metaphase (Fig. 1) can be explained using LC phases. In the mitotic cell, the cytoplasm is both liquid and aligned. This is, in fact, a basic property of LC’s, for they have the mobility of a fluid and the structural order of a solid. Then the spindle is regarded as a bipolar LC assembly with the centrosomes acting as LC poles (centres of LC defects). The centrosomes and the nuclear envelope are both treated as bodies submerged in the LC medium.
Reference:
D. Miroshnychenko, N.A. Hill, N.J. Mottram andJ.E. Lydon, Liquid crystal pre-patterning in mitosis, submitted to the ASME Summer Bioengineering Conference (2005). [pdf]