1 / 51

Cell Division

Cell Division. Morphological changes in M-phase due to protein phosphorylation, dephosphorylation Chromosome condensation: histone NEBD: nuclear lamins Cytoskeletal rearrangement(spindle, contractile ring): caldesmon, c-src. Centrosome cycle. Formation of mitotic spindle pole

Download Presentation

Cell Division

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Cell Division Morphological changes in M-phase due to protein phosphorylation, dephosphorylation Chromosome condensation: histone NEBD: nuclear lamins Cytoskeletal rearrangement(spindle, contractile ring): caldesmon, c-src

  2. Centrosome cycle • Formation of mitotic spindle pole • Independent to nuclear cell cycle • S-phase: centriol replicate • Prophase: centrosome split & move apart • Prometaphase: NEBD mt from each controsome to enter nucleus, & interact with chromosome  spindle pole

  3. Centriol replication

  4. The centrosome cycle Aster formation Polar MT formation

  5. Six steps in M-phase prophase prometaphase metaphase anaphase telophase cytokinesis

  6. Mitosis in an animal cell

  7. Time course for mitosis

  8. Prophase • Chromosome condensation: form 2 sister chromatids held together at centromere • Centrosome split & move apart • Dynamic microtubules: Half life of MT decreased 20X

  9. Prometaphase • Centrosome segregate to the pole • NEBD at early prometaphase • Enables mitotic spindle to interact with chromosome • Formation of mitotic spindle • Kinetochore MT: orientation and movement of chromosomes • Kinetochore act as cap that protect + end from depolymerizing • Centrosome at spindle pole protect – end from depolymerizing

  10. Mitotic spindle

  11. Formation of bipolar mitotic spindle Dynamically unstable + end + end overlap MAP (motors) stabilizes

  12. Separation of two spindle poles in prophase

  13. Kinetochore • Developed from centromere • MT attaches in metaphase • Consist of a specific DNA sequence • Large mutiprotein complex, platelike trilaminar structure • Human; 20-40 MT, yease; 1 MT • A puzzle: how MT & kinetochore connected to each other • * hold on to a MT end, • yet allow that end to add or loose subunits

  14. Centromere in the yeast

  15. Yeast kinetochore

  16. Metaphase • Kinetochore MT align chromosome in metaphase plate • MT are dynamic

  17. Aster exclusion force • The origin is not known • Aligning chromosomes at the spindle Evidence for an astral ejection force

  18. How to align the chromosomes in metaphase plate -> Balanced bipolar force

  19. A model for the centrosome-independent spindle assembly

  20. How MT & kinetochore connected to each other • Microinjection of labeled tubulin: • metaphase; incorporate tubulin near kinetochore • anaphase; reverse action at same site • Puzzle: • Hold on to a MT end, yet allow that end • to add or loose subunits • Sliding collar based model

  21. Microinjection of labeled tubulin: • - metaphase; incorporate tubulin near kinetochore • - anaphase; reverse action at same site

  22. Anaphase • Paired kinetochore separate –> separation & segregation of chromatid • Start abruptly by specific signal • Signal may be intracellular Ca2+ rise: • 1) Rapid, transient 10X increase Ca2+ at anaphase in some cells • 2) Injection of low level of Ca2+ into metaphase cell ->premature anaphase • 3) Accumulation of Ca2+ containing membrane vesicle at spindle pole • 4) Clamp Ca rise by EGTA, BAPTA -> arrest anaphase • **mechanism of Ca2+ rise during anaphase is a mystery • Anaphase A • shortening of kinetochore MT -> poleward movement of chromatids • no energy required for shrinking of kinetochore • Anaphase B • elongation of polar MT -> two spindle poles move further apart • ATP hydrolysis is required for elongation of polar MT; kinesin ATPase • drug chloral hydrate inhibits Anaphase B not A • pulling aster MT -> -end moter binds cell cortex & aster MT • -> pull spindle pole apart

  23. Chromatid separation at anaphase

  24. How kinetochore hold on to a MT end, • yet allow that end to add or loose subunits Motors as anchors

  25. Motor proteins in anaphase B

  26. A model for how motor proteins may act in anaphase B

  27. Telophase • Chromatids separate completely • Kinetochore MT disappears • Polar MT elongate still more • Nuclear envelope reassemble • Nucleoli reappear

  28. Cytokinesis • Begins at anaphase • Cleavage furrow occurs in the plane of metaphase plate, • right angle to the long axis of the mitotic spindle • Aster is responsible for cleavage furrow position • contractile ring: assembles in the early anaphase (actin & myosin II) • myosin dephosphorylation triggers cytokinesis • Midbody: bridge between two cells, contains polar MT • organelles partitioned with no special mechanisms • mitochondria, chloroplasts; grow, fission -> # doubles • ER, Golgi; fragmentation, vesiculation -> even distribution • unequal segregation of cell components • C. elegans “p-granules” to posterior -> form germ line cells • (independent to MT, but dependent on actin filament) • styela yellow cresent (myoplasm) to vegetal -> form muscle • (microfilament first phase, MT second phase)

  29. Asters signal to the cortex to initiate a cleavage furrow

  30. An asymmetric cell division of the nematode egg

  31. Spindle rotation Asymmetric cell division

  32. The contractile ring

More Related