Centrosome Duplication

A centrosome is the main microtubule organizer of a eukaryotic cell and plays a vital role in the formation of the mitotic spindle, a bipolar arrangement of microtubules that separates sister chromatids. The two spindle poles are formed by two oppositely placed centrosomes.

Prior to the cell cycle, however, most animal cells contain only one centrosome in the cytoplasm. The G1/S-cyclin dependent kinase or Cdk complex—consisting of cyclin E and Cdk2 in animal cells—helps trigger centrosome duplication as well as cell cycle entry. 

Each centrosome consists of two centrioles, which are encapsulated by a proteinaceous pericentriolar matrix.

The centrosome duplication starts in the early G1 phase when the separase carries out the disengagement of the two centrioles. A protein belonging to the polo-like protein kinase family, Plk-4, is an important regulator for centriole biogenesis in humans.

Near the onset of S phase, a daughter centriole starts growing at a right angle to the base of each centriole.

During G2, the daughter centrioles typically finish elongating. The four centrioles remain close together in the centrosome until the cell enters mitosis.

At the beginning of mitosis, the centrosome splits in two, which is also known as centrosome disjunction. The two resulting centrosomes each contain a pair of centrioles and the pericentriolar matrix. Both centrosomes nucleate a set of microtubules, primarily at the mother centriole, collectively forming the mitotic spindle.

Centrosome and chromosome life cycle are similar in several aspects. Their duplication occurs only once per cycle and both duplicate through a semiconservative process where a new copy is produced from the pre-existing parent copy.

Also, like chromosomes, one copy of the centrosome is equally distributed to each daughter cell after the division.

Excessive centrosome duplication can impair mitotic spindle assembly and cause chromosomes to segregate improperly, which can cause diseases like cancer.