**4. Cell cycle: Centriole union link**

Polarization of cell division: Recent advances have demonstrated that ciliary proteins are involved in the regulation of the cell cycle. Centrioles play a dual role in the cell. They form the centrosomes that can interconvert with basal bodies upon ciliation. At the same time, they also give rise to the poles of the mitotic spindle. Centrioles may function as a signaling platform, through proteins that promote the transition from one phase to another in mitosis [18].


The Centrosome is an organelle located in the center of eukaryotic cells, and acts as an organizing center rather than a microtubule [19]. The centrosome is known as the cytoskeleton's microtubule organizing center of the eukaryotic cell animal, that radiates in a star way or ASTER during mitosis. Experiments show that centrosome absence prevents the cytogenesis process; the cycle does not progress beyond G1.

The centrosome consists of: a) the *Diplosome,* two cylindrical centrioles arranged perpendicularly, located near the nucleus (9 groups of 3 microtubules in cylindrical provision, diameter of 200 nm and 400 nm long). The centrioles of the centrosome are distinguished by a Mother centriole (mature) and a Daughter one; the *Mother* centriole is associated with proteins forming appendices: distal (related to cilia and flagella; a centriole at the base of each cilium or flagellum) and subdistal, involved in microtubule nucleation. b) the *pericentriolar material*, the dense part of the cytosol (amorphous-looking material) and c) the *aster fibers* (microtubules organized in rays).

The centrosome´s main function is to form and organize the microtubules that comprise the achromatic spindle in division of the cell nucleus. The paternal centrosome plays the motor role in meiosis, while the maternal centrosome disappears. Only the mature mother centriole, likely due to the existence of subdistal appendages, transforms into the peculiar structure at the distal end, the basal body, which gives rise to the cilia and flagella of eukaryotic cells. If certain factors are absent (the ODF2 in mice), the cells are unable to organize cilia or flagella [20].

The centrioles are surrounded by an electron-dense matrix called the pericentriolar material (PCM), composed of sets of proteins that modulate or assist in centrosome involving processes. To this day, genome sequencing and comparison has detected and described about 300 proteins that most likely work with the centrosome, although few of them are well known.

Mutations in intraflagellar transport (IFT) genes have clearly demonstrated a correlation between primary cilia and cell cycle control. The basal body-centrosome complex also plays a crucial role in coordinating IFT and the formation of cilia. The centrosome is surrounded by pericentriolar material (PCM), which serves as a nucleation site for microtubules. In mammalian cells, RNAi knockdown of a protein important for PCM organization, pericentrin, inhibits ciliogenesis and reduces the abundance of IFT components near the centrioles [21]. Mutations in a *Drosophila* pericentrin-like homolog also cause malformations in sensory neuron cilia and sperm, indicating that the pericentrin-mediated interaction between centrosomal and IFT proteins is evolutionarily conserved [22]. Misregulation of cell cycle control is at the basis of oncogenesis. The cancer-promoting proteins Aurora A and HEF1/NEDD9/CAS-L play a role in primary cilium stabilization. Loss of cilia in cancer may contribute to the insensitivity of cancer cells to environmental repressive signals [23].
