mitotic events - early import of cyclin b1-cdk1. disassembly of the nuclear lamina. chromosome...
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Mitotic events - early
• Import of cyclin B1-cdk1.• Disassembly of the nuclear lamina.• Chromosome condensation.• Dissociation of cohesins from chromatid arms.• Separation of centrosomes and assembly of the
mitotic spindle.• Bipolar attachment of the spindle to the
chromosomes.• Release of the mitotic checkpoint.
Mitotic events - early
• Import of cyclin B1-cdk1.• Disassembly of the nuclear lamina.• Chromosome condensation.• Dissociation of cohesins from chromatid arms.• Separation of centrosomes and assembly of the mitotic
spindle.• Bipolar attachment of the spindle to the chromosomes.• Release of the mitotic checkpoint.
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Mitotic events - early
• Import of cyclin B1-cdk1.• Disassembly of the nuclear lamina.• Chromosome condensation.• Dissociation of cohesins from chromatid arms.• Separation of centrosomes and assembly of the mitotic
spindle.• Bipolar attachment of the spindle to the chromosomes.• Release of the mitotic checkpoint.
Mitotic events - early
• Import of cyclin B1-cdk1.• Disassembly of the nuclear lamina.• Chromosome condensation.• Dissociation of cohesins from chromatid arms.• Separation of centrosomes and assembly of the mitotic
spindle.• Bipolar attachment of the spindle to the chromosomes.• Release of the mitotic checkpoint.
The three factors that enable sister chromatid separation
• The pulling force - the mitotic spindle
• The glue - cohesins
• The timing mechanism - spindle checkpoint
Condensins replace cohesins in early mitosis
Mitotic events - early
• Import of cyclin B1-cdk1.• Disassembly of the nuclear lamina.• Chromosome condensation.• Dissociation of cohesins from chromatid arms.• Separation of centrosomes and assembly of the mitotic
spindle.• Bipolar attachment of the spindle to the chromosomes.• Release of the mitotic checkpoint.
Centrosome separation
G1
G2
Prophase
Mitotic events - early
• Import of cyclin B1-cdk1.• Disassembly of the nuclear lamina.• Chromosome condensation.• Dissociation of cohesins from chromatid arms.• Separation of centrosomes and assembly of the mitotic
spindle.• Bipolar attachment of the spindle to the chromosomes.• Release of the mitotic checkpoint.
Fluorescent mad2 on centromeres
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Mitotic events - metaphase
• Activation of the APC/C - degradation of securin - cleavage of Scc1 - Metaphase transition
The story of the two blind men
• Two blind men go into a shop and buy each five different pairs of socks. Unfortunately all ten pairs were packed in the same bag.
• How can the two men separate the socks so that each of them will get five pairs ?
Sister chromatid separation from prometaphase to anaphase
Securin
Separin
Cohesin
metaphase
Securin
Separin
Cohesin
prometaphase
APC
Check
point
Separin
anaphase
APC
Securin
Separin
Non-degradable securin does not prevent cytokinesisbut interferes with complete chromatide separation
histon-GFP Hoechst HeLa
securin
securinKAA-DM
securinKAA-DM
NIH3T3
Time lapse photography of cells expressing non-degradable securin
There is no problem to enter mitosis however at the metaphase transition trouble starts:
Some cell manage relatively well but remain connected by a thin thread of chromatin.
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Time lapse photography of cells expressing non-degradable securin
Some cells just give up and decondense their DNA without dividing at all.
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Mitotic events - late
• Activation of the APC/C - degradation of securin - cleavage of Scc1 - Metaphase transition
• Chromatid segregation.• Degradation of cyclin B1• Reassembly of the nuclear lamina.• Chromosome decondensation.• Cytokinesys
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The Polo kinases
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