CENTROSOME: FUNCTIONS AND STRUCTURE - BIOLOGY - 2025

The centrosome is a membrane-free cell organelle that participates in processes of cell division, cell motility, cell polarity, intracellular transport, organization of the microtubule network, and in the production of cilia and flagella.

Due to its main function it is known as the “organizing center of microtubules”. In most cases, this structure is located very close to the cell nucleus and is strongly associated with the nuclear envelope.

In animal cells, centrosomes are formed by two centrioles immersed in a pericentriolar matrix, rich in different types of proteins. The centrioles are responsible for organizing the microtubules of the spindle.

However, these structures are not essential for the processes of cell division. Indeed, in most plants and other eukaryotes, the centrosomes lack centrioles.

All the centrosomes are of parental origin, since at the moment in which the fertilization occurs, the centrosome of the ovum is inactivated. Therefore, the centrosome that directs post-fertilization cell division processes comes solely from the sperm. Contrary to the mitochondria, for example, which is maternal in origin.

A fairly close relationship has been established between alterations in the centrosomes and the development of cancer cells.

Main functions of the centrosome

In different lineages of eukaryotes, centrosomes are considered multifunctional organelles that perform a significant number of cellular tasks.

The main function of the centrosomes is to organize the microtubules and promote the polymerization of the subunits of a protein called “tubulin”. This protein is the main component of microtubules.

Centrosomes are part of the mitotic apparatus. In addition to the centrosomes, this apparatus includes the mitotic spindle, formed by the microtubules, which are born in each centrosome and connect the chromosomes with the poles of the cells.

In cell division, the equal segregation of chromosomes to daughter cells depends essentially on this process.

When the cell has an uneven or abnormal set of chromosomes, the organism may be unviable or the growth of tumors may be favored.

Secondary functions

Centrosomes are involved in maintaining cell shape and are also involved in membrane movements, since they are directly related to microtubules and other elements of the cytoskeleton.

Recent studies have suggested a new function of the centrosomes, related to the stability of the genome. This is crucial in the normal development of cells and, if it fails, it can lead to the development of various pathologies.

Whether or not animal cells can develop properly in the absence of centrioles is a hotly debated issue in the literature.

Some experts support the idea that although certain animal cells can proliferate and survive in the absence of centrioles, they show aberrant development. On the other hand, there is also evidence that supports the opposite position.

Structure

Centrosomes are made up of two centrioles (a pair, also called diplosomes) surrounded by the pericentriolar matrix.

Centrioles

The centrioles are shaped like cylinders and resemble a barrel. In vertebrates, they are 0.2 µm wide and 0.3 to 0.5 µm long.

In turn, these cylindrical structures are organized into nine ring-shaped microtubule triplets. This ordering is usually denoted as 9 + 0.

The number 9 indicates the nine microtubules and the zero refers to their absence in the central part. Microtubules function as a kind of girder systems that resist cytoskeletal compression.

In the centrosomes there are three types of microtubules, each with a defined function and distribution:

-The astral microtubules, which anchor the centrosome to the cell membrane by means of short extensions.

-The microtubules of the kinetochore (the kinetochore is a structure of the chromosome located in their centromeres), which couple the kinetochore associated with the chromosome with the centrosomes.

-Finally, the polar microtubules, located at both poles of use.

In addition, the centrioles give rise to the basal bodies. Both items are inter-convertible. These are the structures from which the cilia and flagella come, elements that allow locomotion in certain organisms.

Pericentriolar matrix

The matrix or pericentriolar material is a granular and quite dense area of ​​the cytoplasm. It is made up of a varied set of proteins.

The main proteins in this amorphous matrix are tubulin and pericentrin. Both have the ability to interact with microtubules for the union of chromosomes.

Specifically, it is the ɣ tubulin rings that serve as nucleation sites for the development of microtubules that then radiate out of the centrosome.

Centrosomes and the cell cycle

The size and composition of proteins in centrosomes vary substantially during different stages of the cell cycle. To replicate, the centrosomes do it from a pre-existing one.

Interphase cells contain only one centrosome. This is duplicated only once during the cell cycle and gives rise to two centrosomes.

In the G1 phase of the cycle, the two centrioles are oriented orthogonally (forming an angle of 90 degrees), which is their characteristic position.

When the cell passes the G1 phase, an important checkpoint of the cell cycle, DNA replicates and cell division occurs. At the same time, the replication of the centrosomes begins.

At this point the two centrioles are separated by a short distance, and each original centriole gives rise to a new one. Apparently this synchronization of events occurs by the action of enzymes called kinases.

In the G ₂ / M phase, the duplication of the centrosomes is completed and each new centrosome is composed of a new and an old centriole. This process is known as the centrosome cycle.

These two centrioles, also known as the "mother" centriole and the "child" centriole, are not completely identical.

The mother centrioles have extensions or appendages that can serve to anchor microtubules. These structures are absent in the daughter centrioles.

References

1. Alieva, IB, & Uzbekov, RE (2016). Where are the limits of the centrosome? Bioarchitecture, 6 (3), 47-52.
2. Azimzadeh, J. (2014). Exploring the evolutionary history of centrosomes. Philosophical Transactions of the Royal Society of London. Series B, 369 (1650), 20130453.
3. Azimzadeh, J., & Bornens, M. (2007). Structure and duplication of the centrosome. Journal of cell science, 120 (13), 2139-2142.
4. D'Assoro, AB, Lingle, WL, & Salisbury, JL (2002). Centrosome amplification and the development of cancer. Oncogene, 21 (40), 6146.
5. Kierszenbaum, A., & Tres, L. (2017). Histology and cell biology. Introduction to pathological anatomy. Second edition. Elsevier.
6. Lerit, DA, & Poulton, JS (2016). Centrosomes are multifunctional regulators of genome stability. Chromosome research, 24 (1), 5-17.
7. Lodish, H. (2005). Cellular and molecular biology. Editorial Médica Panamericana.
8. Matorras, R., Hernández, J., & Molero, D. (2008). Treatise on human reproduction for nursing. Pan American.
9. Tortora, GJ, Funke, BR, & Case, CL (2007). Introduction to microbiology. Editorial Médica Panamericana.