Mitotic events — early Import

Mitotic events - early • • • Import of cyclin B 1 -cdk 1. 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 B 1 -cdk 1. 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 G 1 G 2 Prophase

Mitotic events - early • • • Import of cyclin B 1 -cdk 1. 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 mad 2 on centromeres

Mitotic events - metaphase • Activation of the APC/C - degradation of securin cleavage of Scc 1 - 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 Check APC Separin point Securin Separin Cohesin prometaphase Cohesin metaphase Securin anaphase

Non-degradable securin does not prevent cytokinesis but interferes with complete chromatide separation NIH 3 T 3 securin KAA-DM histon-GFP Hoechst He. La

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.

Time lapse photography of cells expressing non-degradable securin Some cells just give up and decondense their DNA without dividing at all.

Mitotic events - late • Activation of the APC/C - degradation of securin cleavage of Scc 1 - Metaphase transition • Chromatid segregation. • Degradation of cyclin B 1 • Reassembly of the nuclear lamina. • Chromosome decondensation. • Cytokinesys

The Polo kinases