sister chromatid biorientation

Definition

Target type: biologicalprocess

The cell cycle process in which sister chromatids establish stable attachments to microtubules emanating from opposite spindle poles. [PMID:15309047]

Sister chromatid biorientation is a crucial step in cell division that ensures the accurate segregation of chromosomes to daughter cells. It involves the attachment of sister chromatids, which are identical copies of a chromosome, to opposite poles of the spindle, a microtubule-based structure that pulls chromosomes apart.

This process is orchestrated by a complex interplay of proteins and microtubules. Key players include:

- **Kinetochores:** These protein complexes assemble at the centromere, the constricted region of a chromosome where sister chromatids are joined. Kinetochores serve as attachment points for microtubules.

- **Microtubules:** These are dynamic polymers of tubulin protein that emanate from the centrosomes, which act as microtubule organizing centers. Microtubules attach to kinetochores, forming kinetochore fibers.

- **Motor proteins:** These proteins, like dynein and kinesin, move along microtubules and help regulate the attachment and movement of chromosomes.

Here's a step-by-step breakdown of sister chromatid biorientation:

1. **Initial Capture:** Microtubules from both poles of the spindle attach to the kinetochores of sister chromatids. This initial capture is often unstable and can lead to incorrect attachments where both sister chromatids are attached to the same pole.

2. **Tension Sensing and Correction:** The cell monitors tension on kinetochore fibers. If tension is low or absent, it signals a need for correction. This triggers a process called "error correction," where incorrect attachments are broken and new attachments are established.

3. **Stable Biorientation:** When sister chromatids are attached to opposite poles and experience equal tension, they achieve stable biorientation. This stable state signals that the cell is ready to proceed to chromosome segregation.

4. **Chromosome Segregation:** Once all chromosomes are bioriented, the spindle fibers shorten, pulling sister chromatids apart and segregating them to opposite poles of the cell.

Proper sister chromatid biorientation is essential for maintaining genomic integrity. Errors in this process can lead to aneuploidy, a condition where cells have an abnormal number of chromosomes, which can contribute to cancer and developmental disorders.'
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