- Cyclin B1 is the main B-type cyclin, which regulates cell cycle progression during the transition from interphase to mitosis as well as the early stages of mitosis.
- Cyclin B1 synthesis starts at the end of the S-phase and peaks during the G2/M phase transition.
- Tissue expression: Cyclin B1 is expressed in most dividing cells.
- Subcellular localization during cell cycle progression:
- In the G2 phase, cyclin B1 is localized in the cytoplasm.
- Accumulation of cyclin B1 on the centrosome starts in the mid-G2 phase. In late G2, the local concentration of cyclin B1 is highest at the centrosomes.
- In prophase (first phase of M-phase), just before the nuclear envelope breakdown, it rapidly enters the nucleus. During prophase, it mostly localizes in the nucleus, however, a good amount of cyclin B1 is also observed in the cytoplasm.
- During mitosis, after the breakdown of the nuclear envelope, it is present everywhere. Degradation of cyclin B1 starts at the beginning of the anaphase. Cyclin B1 disappears in anaphase.
- Disruption of the cyclin B1 gene in mice results in embryonic lethality in utero.
- The promoter of Cyclin B1 contains CCAAT boxes. Trimeric transcriptional activator NF-Y binds to this site and regulates their transcription.
- Expression of cyclin B1 starts at the end of the S-phase and peak at the late G2 phase. However, activation of the CDK1-cyclin B1 complex does not occur in the G2 phase.
- Activation of CDK1-cyclin B1 complex occurs during the prophase of mitosis in the cytoplasm, before nuclear envelope breakdown. Initial activation of CDK1-cyclin B1 complex takes place at the centrosome.
- Active CDK1-cyclin B1 complex play a crucial role in many mitotic processes like cell rounding, centrosome separation, mitotic spindle formation, nuclear envelope breakdown, and chromosome condensation.
- CDK1-cyclin B1 complex phosphorylates many substrates which are present both in the cytoplasm as well as in the nucleus.
- Cytoskeleton microtubule
- Actin
- Intermediate filament networks
- Caspases
- Golgi apparatus
- Nuclear lamins
- Nuclear pore complexes
- Anaphase-promoting complex/cyclosome
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