Centrosome Duplication: Role in Modern Cell Division

Centrosome duplication is a crucial process ensuring proper cell division, influencing chromosome segregation and overall cellular organization. Errors in this process can lead to aneuploidy or tumorigenesis, highlighting its significance in both normal development and disease.

Role In Cell Cycle Progression

Centrosome duplication is tightly regulated to ensure each daughter cell inherits precisely one centrosome, maintaining genomic stability. This process begins in late G1 phase and completes by the end of S phase, controlled by cyclin-dependent kinases (CDKs) and Polo-like kinases (PLKs). These enzymes initiate centriole separation, the core structural components of the centrosome. Disruptions in this regulation can lead to supernumerary centrosomes, resulting in multipolar spindles and chromosome missegregation, a hallmark of many cancers.

As the cell enters S phase, the engagement between the mother and daughter centrioles loosens, allowing new procentrioles to form. This process is mediated by SAS-6, which forms the cartwheel structure serving as a scaffold for procentriole assembly. The recruitment of pericentriolar material (PCM) components, including γ-tubulin, supports microtubule nucleation, ensuring centrosomes effectively organize the mitotic spindle. Proper duplication and maturation of centrosomes are essential for spindle orientation, influencing asymmetric cell division in stem cells and tissue homeostasis.

During mitosis, centrosomes mature by accumulating PCM proteins such as pericentrin and CDK5RAP2, enhancing microtubule-organizing capacity. This maturation is crucial for forming a robust bipolar spindle, ensuring equal chromosome segregation. Centrosome positioning also determines the plane of cytokinesis, influencing daughter cell fate in developing tissues. Errors in duplication or function can lead to aneuploidy, frequently observed in aggressive cancers.

Molecular Components And Assembly

Centrosome duplication relies on a coordinated interplay of structural proteins and regulatory factors. At the core are centrioles, cylindrical microtubule-based structures composed of nine triplet microtubules arranged in radial symmetry. Procentriole assembly is initiated by SAS-6, which forms the cartwheel structure dictating centriole symmetry. This cartwheel recruits additional components, including STIL and CPAP, which extend and stabilize the growing centrioles. Controlled polymerization ensures uniform centriole development, preventing defects that could compromise spindle organization.

Beyond centrioles, the PCM provides a dynamic matrix supporting microtubule nucleation and centrosome maturation. Proteins such as pericentrin and CDK5RAP2 act as scaffolds within the PCM, facilitating the recruitment of γ-tubulin ring complexes (γ-TuRCs). These complexes serve as nucleation sites for microtubule growth, ensuring centrosomes function as robust microtubule-organizing centers (MTOCs). PCM expansion during maturation enhances microtubule anchoring, increasing spindle stability and ensuring efficient chromosome segregation. Disruptions in PCM assembly reduce centrosome functionality, leading to mitotic errors and genomic instability.

Polo-like kinase 4 (PLK4) is the master regulator of centriole biogenesis, initiating procentriole assembly by phosphorylating STIL and SAS-6. This phosphorylation promotes the recruitment of CP110 and CEP135, stabilizing the growing centriole. The ubiquitin-proteasome system ensures centrosome duplication occurs only once per cell cycle, targeting excess PLK4 for degradation to prevent supernumerary centrosomes. Mutations affecting PLK4 or its degradation pathways are linked to centrosome amplification, contributing to chromosomal instability in cancer.

Coordination With DNA Replication

The synchronization of centrosome duplication with DNA replication is essential for maintaining genomic integrity. Both processes begin in late G1 phase and progress through S phase under shared regulatory mechanisms involving CDKs and checkpoint pathways. Disruptions in this balance can result in centrosome amplification or DNA damage, both contributing to chromosomal instability in malignancies.

CDK2, in association with cyclin E, triggers both DNA synthesis and centrosome duplication. CDK2 phosphorylates nucleophosmin, which dissociates from the centrosome upon activation, initiating procentriole formation. Simultaneously, CDK2 promotes the loading of replication factors onto origins of replication, ensuring DNA synthesis progresses in parallel with centrosome duplication. Proper timing prevents premature centriole disengagement or incomplete DNA replication, reducing errors during cell division.

Checkpoint mechanisms reinforce this coordination by halting cell cycle progression if replication stress or DNA damage is detected. ATR kinase, activated by replication fork stalling, stabilizes replication forks and suppresses centrosome reduplication by inhibiting PLK4. Similarly, the p53 tumor suppressor prevents centrosome amplification under genomic stress by inducing p21, a CDK inhibitor that restrains duplication. Loss of these controls is common in cancer, where centrosome amplification and aneuploidy drive tumor progression.

Microscopy And Labeling Methods

Advanced microscopy techniques and precise labeling strategies are essential for visualizing centrosome duplication. Super-resolution microscopy, including stimulated emission depletion (STED) and structured illumination microscopy (SIM), provides the resolution needed to distinguish individual centrioles and PCM organization. These techniques reveal the nanoscale architecture of centrosomes, allowing researchers to observe duplication steps in detail. Live-cell imaging using fluorescence recovery after photobleaching (FRAP) enables the study of centrosomal protein dynamics, shedding light on how key regulators are recruited and exchanged over time.

Fluorescent labeling strategies aid centrosome visualization, with antibodies against γ-tubulin, pericentrin, and CEP192 highlighting the PCM, while centriolar proteins such as SAS-6 and CP110 mark procentriole assembly. Genetically encoded fluorescent proteins, including GFP-tagged centrin or mCherry-tagged PLK4, allow real-time tracking of centrosome duplication in living cells. These methods have been instrumental in identifying aberrant duplication events associated with disease, offering insights into how centrosome dysregulation contributes to pathology.

Abnormal Duplication In Health

Errors in centrosome duplication have profound consequences for cellular function and disease. When centrosomes duplicate excessively or fail to segregate properly, cells acquire supernumerary centrosomes, leading to multipolar spindles and disrupted chromosome segregation. This increases the likelihood of aneuploidy, a hallmark of many aggressive cancers. Centrosome amplification is frequently observed in breast, ovarian, and pancreatic cancers, where it promotes chromosomal instability and tumor progression. Excess centrosomes can also alter cell polarity and adhesion, enabling cancer cells to spread more efficiently.

Beyond cancer, centrosome abnormalities are linked to neurodevelopmental disorders such as microcephaly and primordial dwarfism. Mutations in genes encoding centrosomal proteins, including CEP152 and CDK5RAP2, have been identified in patients with autosomal recessive primary microcephaly, a condition characterized by reduced brain size due to defective neural progenitor proliferation. Centrosome dysfunction in these disorders disrupts spindle orientation and asymmetric cell division, impairing neural stem cell expansion during early brain development. Research continues to uncover therapeutic targets, with efforts aimed at modulating centrosome duplication as a strategy to address both cancer and neurodevelopmental disorders.