שכפול Centrosome

Centrosome duplication is the process by which a cell replicates its centrosome to produce two centrosomes before cell division. This duplication occurs during the cell cycle, typically beginning in G1 phase and completing by the end of S phase. Each daughter centrosome contains a pair of centrioles and serves as a microtubule-organizing center essential for proper cell division.

Centrosome duplication is critical because the two resulting centrosomes organize and nucleate microtubules that form the spindle apparatus during mitosis and cytokinesis. Without proper duplication, cells cannot establish bipolar spindles needed for accurate chromosome segregation and successful cell division. This ensures each daughter cell receives the correct genetic material.

A centrosome consists of two centrioles arranged perpendicular to each other, surrounded by pericentriolar material (PCM). The centrioles are cylindrical structures composed of microtubules, while the PCM contains proteins that nucleate and organize microtubules. Together, these components enable the centrosome to function as the cell's primary microtubule-organizing center.

The centrosome cycle is tightly coordinated with the cell cycle, ensuring centrosome duplication occurs once per cell cycle. Duplication begins in G1 phase and completes by late S phase, so two centrosomes are available for spindle formation during mitosis. This synchronization prevents centrosome over-duplication and maintains genomic stability across cell divisions.

Centrosomes nucleate and organize microtubules into radial arrays that extend throughout the cell. During interphase, centrosomes organize the cytoplasmic microtubule network that supports cell shape and transport. During cell division, the two centrosomes organize microtubules into the bipolar spindle that separates chromosomes and organizes the cell for cytokinesis.

Abnormal centrosome duplication can lead to multipolar spindles, chromosome missegregation, and aneuploidy, potentially causing cell death or cancer development. Conversely, failure to duplicate centrosomes results in monopolar spindles and improper chromosome segregation. Both scenarios disrupt normal cell division and can compromise cellular viability and genomic stability.

Cells regulate centrosome duplication through licensing and re-licensing mechanisms controlled by cell cycle checkpoints and kinases. Licensing factors allow duplication during G1 phase, but are inactivated during S and G2 phases to prevent re-duplication. This tight regulation ensures exactly two centrosomes exist before division, maintaining proper spindle formation and chromosome segregation.