The position of the yeast nucleus in early mitosis (top) determines where the contractile ring forms (red arrow; bottom).


The mitotic spindle sets the division plane in mammalian cells. But fission yeast instead use their nuclei to position the division plane during mitosis, say Rafael Daga and Fred Chang (Columbia University, New York, NY).

Based on previous research implicating the nucleus in plant and fungi cell division, the authors investigated the consequence of repositioning the nucleus to one end of the cell by spinning cells at low speeds. Asymmetric cell division ensued if the nucleus did not migrate back to the center before mitosis.

Moving the nucleus during interphase resulted in a single displaced contractile ring, whereas moving it during early mitosis caused multiple rings or ring fragments to develop. If positioned close enough together, the fragments coalesced before division. Daga and Chang suspect that ring compaction, which normally occurs during ring assembly, may also bring together ring fragments, thus avoiding the formation of multiple division sites.

Chang previously observed that the position of mid1 on the cell surface tracks with the movement of the nucleus. As mid1 is required for ring positioning, Chang thinks that the nucleus may use this protein to communicate with the contractile ring. He suspects that “something is physically connecting mid1 to the nucleus.” He and his coworkers have already ruled out actin or microtubules as this tethering material, so they are now examining less obvious candidates.


Daga, R.R., and F. Chang.
Proc. Natl. Acad. Sci. USA.