Following my review of the major eukaryotic cytoskeleton components, and microtubules in particular…
A pair of centrioles is shown, each with ninefold symmetry owing to the nine triplet microtubules. Each centriole has pericentriolar material that nucleates microtubules around the ends closest to one another. Only the maternal centriole has two sets of extra appendages, distal and subdistal; the latter seems to anchor microtubules. A series of interconnecting fibres, different from the pericentriolar material (PCM), links the closest ends of the two centrioles.
The centrosome is the main microtubule organizing center (MTOC) of the cell as well as a regulator of cell-cycle progression. It was discovered in 1888 by Theodor Boveri and was described as the ‘special organ of cell division.’ Although the centrosome has a key role in efficient cell division, it has been recently shown that it is not necessary.
The centrosome is duplicated only once per cell cycle so that each daughter cell inherits one centrosome, containing two centrioles. The centrosome replicates during the S phase of the cell cycle. During the prophase of mitosis, the centrosomes migrate to opposite poles of the cell. The mitotic spindle then forms between the two centrosomes. Upon division, each daughter cell receives one centrosome. Aberrant numbers of centrosomes in a cell have been associated with cancer.
So, how is centrosome duplication regulated, and in particular, how is the mitotic spindle formed? This is a hot topic that I’ve begun to pay more attention to, and previous studies have identified a few participants in this process, but left gaping holes in our understanding of how such components control and carry out duplication.
As shown (from Doxsey, 2001), proteins that are involved in centrosome separation and spindle formation include Nek2, Plk1, Aurora A, NuMa and TPX2, among others.
These components are in various ways very interdependent, and each necessary in their own right, for duplication and separation to proceed. But how do they interact with the centrioles or pericentriolar material, or each other, and other candidate proteins?
- Doxsey S. Re-evaluating centrosome function. Nat Rev Mol Cell Biol. 2001 Sep;2(9):688-98.
- Azimzadeh J, Bornens M. Structure and duplication of the centrosome. J Cell Sci. 2007 Jul 1;120(Pt 13):2139-42.
- Nigg EA. Centrosome duplication: of rules and licenses. Trends Cell Biol. 2007 May;17(5):215-21.
- Tsou MF, Stearns T. Mechanism limiting centrosome duplication to once per cell cycle. Nature. 2006 Aug 24;442(7105):947-51.
- Centrosome wiki