A centrosome is a cellular organelle that serves as the primary microtubule-organizing center (MTOC) in most animal cells and plays a central role in cell division, intracellular organization, and the formation of the mitotic spindle. Located near the nucleus, the centrosome usually contains a pair of centrioles surrounded by a protein-rich matrix called the pericentriolar material (PCM). By organizing microtubules, centrosomes help maintain cell shape, position organelles, direct intracellular transport, and ensure accurate chromosome segregation during mitosis and meiosis.
The centrosome is one of the most important structural organizers in eukaryotic cells. During interphase, it helps arrange the cytoskeleton and coordinate cell polarity. Before cell division, the centrosome duplicates so that two centrosomes can form opposite spindle poles. Defects in centrosome number or structure are associated with cancer, developmental disorders, infertility, and neurodegenerative disease. Although centrosomes are characteristic of most animal cells, many plants and fungi lack true centrosomes and instead organize microtubules using alternative structures.
Key Takeaways: Centrosome
- A centrosome is the main microtubule-organizing center in most animal cells.
- It usually contains two centrioles surrounded by pericentriolar material.
- Centrosomes help organize the cytoskeleton and form the mitotic spindle during cell division.
- Most animal cells contain one centrosome during interphase and two before mitosis.
- Higher plants and many fungi do not have true centrosomes.
- Centrioles and centrosomes are related but not identical structures.
- Abnormal centrosome number or function is linked to cancer and developmental disease.
- Centrosomes evolved early in eukaryotic evolution and are closely associated with cilia and flagella.
History of Centrosome Discovery and Study
The centrosome was first described in the late nineteenth century during the rise of modern microscopy and cell biology. In 1888, German anatomist and cell biologist Theodor Boveri coined the term “centrosome” while studying sea urchin embryos. Boveri recognized that the structure played a role in organizing the spindle apparatus during cell division.
At roughly the same time, Belgian cytologist Edouard Van Beneden observed similar structures in dividing cells and connected them to chromosome movement. Early cell biologists debated whether the centrosome represented a permanent organelle or simply a transient accumulation of spindle material.
The invention of electron microscopy in the twentieth century revealed the detailed structure of centrioles and the surrounding pericentriolar material. Researchers discovered the characteristic arrangement of microtubules within centrioles and demonstrated that centrosomes organize cytoplasmic microtubules.
Modern molecular biology transformed centrosome research further by identifying proteins involved in centrosome duplication, spindle assembly, and microtubule nucleation. Scientists also discovered links between centrosome defects and cancer, microcephaly, ciliopathies, and chromosomal instability.
What Is a Centrosome?
A centrosome is a non-membrane-bound organelle that organizes microtubules in animal cells. It acts as the primary microtubule-organizing center by nucleating and anchoring microtubules.
The centrosome typically consists of:
- Two centrioles
- Pericentriolar material (PCM)
The centrioles are cylindrical structures composed mainly of microtubules. The PCM is a dense collection of proteins surrounding the centrioles. Important PCM proteins include gamma-tubulin and associated complexes that initiate microtubule formation.
During much of the cell cycle, the centrosome remains close to the nucleus. As the cell prepares to divide, the centrosome duplicates and the two centrosomes migrate to opposite sides of the cell to establish the poles of the mitotic spindle.
Description and Structure of the Centrosome
Location
The centrosome usually lies in the cytoplasm near the nucleus. In many animal cells, it occupies a central position from which microtubules radiate outward through the cytoplasm.
Number
Most animal cells contain:
- One centrosome during interphase
- Two centrosomes after duplication and during mitosis
Each daughter cell normally inherits one centrosome following cell division.
Appearance
Under a light microscope, centrosomes often appear as a small dense region near the nucleus. Electron microscopy reveals a pair of perpendicular centrioles surrounded by amorphous pericentriolar material.
Centrioles
Each centriole is a short cylindrical structure composed of nine triplets of microtubules arranged in a ring.
The typical centriole structure is often summarized as:
- Nine microtubule triplets
- No central microtubules
This arrangement differs from the “9 + 2” pattern found in cilia and flagella.
The two centrioles within a centrosome are usually oriented at right angles to each other:
- Mother centriole
- Daughter centriole
The mother centriole contains appendages that help anchor microtubules and initiate cilium formation.
Pericentriolar Material
The PCM is a protein-rich matrix surrounding the centrioles. It contains proteins involved in:
- Microtubule nucleation
- Microtubule anchoring
- Cell cycle regulation
- Spindle formation
Gamma-tubulin ring complexes within the PCM serve as templates for microtubule assembly.
Which Cells Have Centrosomes?
Cells That Have Centrosomes
True centrosomes are characteristic of most animal cells, including:
- Epithelial cells
- Muscle cells
- Neurons
- Stem cells
- Many protozoa
These cells use centrosomes to organize microtubules and coordinate cell division.
Cells That Lack Centrosomes
Several groups of organisms either lack centrosomes entirely or use alternative microtubule-organizing centers.
Examples include:
- Higher plant cells
- Most fungi
- Some differentiated animal cells
Plant cells organize microtubules using dispersed nucleation sites rather than a centralized centrosome. Fungi often use spindle pole bodies instead of centrosomes.
Some mature animal cells also lose functional centrosomes during differentiation. For example:
- Mammalian red blood cells lose organelles entirely
- Certain muscle cells have reduced centrosomal activity
- Some neurons reorganize microtubules independently of centrosomes
Functions of Centrosomes
Microtubule Organization
The primary function of the centrosome is organizing microtubules. Microtubules radiate outward from the centrosome to form part of the cytoskeleton.
These microtubules help:
- Maintain cell shape
- Position organelles
- Support intracellular transport
- Establish cell polarity
Mitotic Spindle Formation
During mitosis, centrosomes duplicate and move apart to establish spindle poles. The spindle apparatus attaches to chromosomes and separates sister chromatids into daughter cells.
Without proper centrosome function, chromosome segregation errors can occur.
Cell Polarity and Migration
Centrosomes help determine cell polarity by orienting microtubules within the cell. Migrating cells often position the centrosome toward the leading edge of movement.
Cilia and Flagella Formation
Centrioles can become basal bodies that nucleate cilia and flagella. These structures are important for:
- Cell motility
- Fluid movement
- Sensory signaling
Cell Cycle Regulation
Centrosomes coordinate with the cell cycle machinery to ensure proper timing of duplication and mitosis.
Centrosomes vs. Centrioles
Although the terms are sometimes used interchangeably, centrosomes and centrioles are not the same thing.
| Feature | Centrosome | Centriole |
|---|---|---|
| Definition | Entire microtubule-organizing organelle | Cylindrical microtubule structure |
| Components | Two centrioles plus PCM | Nine microtubule triplets |
| Function | Organizes microtubules and spindle | Structural component of centrosome |
| Number | Usually one per cell in interphase | Usually two per centrosome |
| Presence in Plants | Generally absent | Usually absent |
A centrosome includes centrioles, but centrioles alone do not constitute a complete centrosome.
Centrosome vs Basal Body
Basal bodies and centrosomes are closely related structures because basal bodies originate from centrioles.
| Feature | Centrosome | Basal Body |
|---|---|---|
| Primary Role | Organizes microtubules and spindle | Anchors cilia and flagella |
| Location | Near nucleus | Base of cilium or flagellum |
| Structure | Centrioles plus PCM | Modified centriole |
| Main Function | Cell division and organization | Cilium formation |
| Associated Structures | Mitotic spindle | Cilia and flagella |
A mother centriole can transition into a basal body when the cell forms a cilium.
Centrosomes and Primary Cilia
The centrosome is closely linked to the formation of cilia. In many cells, the mother centriole transforms into a basal body that anchors a primary cilium at the cell surface.
Primary cilia are usually nonmotile sensory structures that detect extracellular signals and help regulate cellular responses.
Primary cilia participate in signaling pathways including:
- Hedgehog signaling
- Wnt signaling
- PDGF signaling
Because basal bodies originate from centrioles, centrosome defects can impair cilia formation and function.
Defective cilia are associated with ciliopathies, a group of disorders that may affect:
- Kidneys
- Eyes
- Brain
- Skeleton
- Respiratory system
Centrosome-Associated Proteins
Many specialized proteins regulate centrosome structure, duplication, and microtubule organization.
Gamma-Tubulin
Gamma-tubulin is essential for microtubule nucleation. It forms gamma-tubulin ring complexes within the pericentriolar material that act as templates for new microtubules.
Pericentrin
Pericentrin is a major scaffolding protein within the PCM. It helps anchor microtubule-organizing proteins around the centrioles.
SAS-6
SAS-6 plays a key role in centriole assembly. It helps establish the ninefold symmetry characteristic of centrioles.
PLK4
Polo-like kinase 4 (PLK4) regulates centriole duplication. Excess PLK4 activity can produce too many centrioles.
CEP Proteins
Centrosomal proteins (CEP proteins) contribute to centrosome stability, spindle formation, and cilia assembly.
Mutations affecting centrosomal proteins are associated with developmental disorders and cancer.
Centrosome Duplication
Centrosome duplication occurs once per cell cycle to ensure that daughter cells inherit the correct number of centrosomes.
The process generally follows these steps:
- Existing centrioles separate slightly.
- A new daughter centriole forms beside each old centriole.
- The centrosome matures during the cell cycle.
- Two centrosomes organize the mitotic spindle during mitosis.
Centrosome duplication is tightly regulated. Errors can produce abnormal centrosome numbers and chromosomal instability.
Centrosome Aberrations and Clinical Significance
Abnormal centrosomes are associated with many diseases.
Cancer
Many cancer cells contain extra centrosomes. Centrosome amplification can lead to:
- Multipolar spindles
- Chromosome missegregation
- Aneuploidy
- Genomic instability
These abnormalities contribute to tumor progression and malignancy.
Cancer cells sometimes cluster extra centrosomes into two spindle poles to survive despite centrosome amplification.
Microcephaly
Mutations in centrosome-associated proteins can disrupt neural stem cell division and brain development, causing primary microcephaly.
Ciliopathies
Because centrioles form basal bodies, centrosome defects can impair cilia formation and function. Disorders linked to defective cilia include:
- Polycystic kidney disease
- Bardet-Biedl syndrome
- Joubert syndrome
Infertility
Abnormal centrosome inheritance or centriole defects can impair sperm function and early embryonic development.
Neurodegenerative Disease
Researchers are investigating links between centrosome dysfunction and neurodegenerative disorders involving abnormal cell organization or impaired intracellular transport.
Centrosome Disorders Table
Defects involving centrosomes and centrioles are associated with multiple human diseases.
| Disorder | Centrosome-Related Defect | Major Effect |
|---|---|---|
| Cancer | Centrosome amplification | Chromosomal instability |
| Primary Microcephaly | Defective spindle orientation | Reduced brain size |
| Polycystic Kidney Disease | Ciliary dysfunction | Kidney cyst formation |
| Bardet-Biedl Syndrome | Basal body defects | Multisystem disorder |
| Joubert Syndrome | Defective cilia signaling | Neurological abnormalities |
| Infertility | Sperm centriole abnormalities | Impaired fertilization |
| Seckel Syndrome | Centrosome protein mutations | Growth and developmental defects |
Centrosome Abnormalities in Aging
Centrosome function can decline with age. Aging cells may develop abnormalities such as:
- Centrosome fragmentation
- Defective spindle assembly
- Chromosome segregation errors
- Aneuploidy
These defects contribute to genomic instability and cellular senescence.
Researchers are investigating whether age-related centrosome dysfunction contributes to neurodegenerative disease, impaired tissue regeneration, and cancer susceptibility.
Evolutionary History of Centrosomes
Centrosomes likely evolved early in eukaryotic evolution alongside the microtubule cytoskeleton and motile cilia.
Centrioles are closely related evolutionarily to basal bodies, which organize cilia and flagella. Many scientists believe these structures share a common ancestral origin.
Not all eukaryotes retained centrosomes during evolution. Plants and fungi evolved alternative methods for organizing microtubules, demonstrating that centrosomes are not absolutely required for eukaryotic life.
The evolutionary conservation of centriole-associated proteins across diverse species suggests that centrosome-related structures originated very early in eukaryotic history.
Experimental Study of Centrosomes
Scientists study centrosomes using several advanced imaging and molecular techniques.
Fluorescence Microscopy
Researchers label centrosomal proteins with fluorescent dyes or fluorescent proteins such as GFP. This allows visualization of centrosome movement and spindle formation in living cells.
Immunostaining
Antibodies against proteins such as gamma-tubulin and pericentrin help identify centrosomes in fixed cells.
Electron Microscopy
Electron microscopy reveals the ultrastructure of centrioles, including the characteristic arrangement of microtubule triplets.
Laser Ablation Experiments
Scientists can selectively damage centrosomes using lasers to study how cells respond to centrosome loss or spindle disruption.
These approaches have greatly improved understanding of cell division and cytoskeletal organization.
Common Misconceptions
Centrosomes and Centrioles Are the Same Thing
A centriole is one structural component of a centrosome. The centrosome also includes the surrounding pericentriolar material.
All Cells Have Centrosomes
Many eukaryotic cells lack true centrosomes. Higher plants and most fungi organize microtubules using different structures.
Centrosomes Contain DNA
Unlike mitochondria and chloroplasts, centrosomes do not contain their own DNA.
Centrosomes Are Membrane-Bound Organelles
Centrosomes lack a surrounding membrane. They are organized protein assemblies within the cytoplasm.
Centrosomes Only Function During Cell Division
Centrosomes also organize the interphase cytoskeleton, establish polarity, and contribute to intracellular transport.
FAQs
What does a centrosome do?
A centrosome organizes microtubules and helps form the mitotic spindle during cell division.
Where is the centrosome located?
The centrosome is usually located near the nucleus in animal cells.
How many centrosomes does a cell have?
Most animal cells contain one centrosome during interphase and two during mitosis.
Are centrosomes found in plant cells?
Higher plant cells lack true centrosomes and instead organize microtubules using dispersed nucleation sites.
What is the difference between a centrosome and a centriole?
A centrosome consists of two centrioles plus surrounding pericentriolar material. A centriole is only one cylindrical structural component.
Why are centrosomes important in cancer?
Abnormal centrosome number can disrupt chromosome segregation and promote genomic instability, which contributes to cancer development.
Do centrosomes contain DNA?
No. Centrosomes do not contain genetic material.
Can cells divide without centrosomes?
Some cells can divide without centrosomes using alternative spindle-organizing mechanisms, although centrosomes improve the efficiency and accuracy of spindle formation in many animal cells.
References and Further Reading
- Azimzadeh, Juliette; Wong, Mei Lie; Downhour, Diane Miller; Alvarado, Alejandro Sánchez; Marshall, Wallace F. (2012). “Centrosome Loss in the Evolution of Planarians”. Science. 335: 461–463. doi:10.1126/science.1214457
- Bornens, M.; Azimzadeh, J. (2008). “Origin and Evolution of the Centrosome”. Eukaryotic Membranes and Cytoskeleton. Advances in Experimental Medicine and Biology. 607: 119–129. doi:10.1007/978-0-387-74021-8_10. ISBN 978-0-387-74020-1.
- Mahoney, N. M.; Goshima, G.; Douglass, A. D.; Vale, R. D. (2006). “Making Microtubules and Mitotic Spindles in Cells without Functional Centrosomes”. Current Biology. 16 (6): 564–569. doi:10.1016/j.cub.2006.01.053
- Marshall, W. F. (2009). “Centriole evolution”. Current Opinion in Cell Biology. 21 (1): 14–15. doi:10.1016/j.ceb.2009.01.008
- Schatten, H; Sun, Q.Y. (2009). “The role of centrosomes in mammalian fertilization and its significance for ICSI”. Molecular Human Reproduction. 15 (9): 531–8. doi:10.1093/molehr/gap049