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

4. 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

6. Centriol replication

7. The centrosome cycle
Aster formation
Polar MT formation

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

9. Mitosis in an animal cell

14. Time course for mitosis

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

16. 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

17. Mitotic spindle

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

21. Separation of two spindle poles in prophase

23. Kinetochore MT attaches in metaphase
Developed from centromere
MT attaches in metaphase
Consist of a specific DNA sequence
Large mutiprotein complex, platelike trilaminar structure
Human; 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

25. Centromere in the yeast

26. Yeast kinetochore

27. Metaphase Kinetochore MT align chromosome in metaphase plate
MT are dynamic

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

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

32. A model for the centrosome-independent
spindle assembly

33. 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

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

35. Anaphase **mechanism of Ca2+ rise during anaphase is a mystery
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

36. Chromatid separation at anaphase

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

38. Motor proteins in anaphase B

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

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

42. 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)

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

45. An asymmetric cell division of the nematode egg

46. Spindle rotation
Asymmetric cell division

49. The contractile ring

51. Mitosis without cytokinesis
in the fly embryo