1. Cytokinesis and Cell plate PCDU seminar winter term 2015/16
Nabila Riaz

2. Overview of the talk Cytokinesis Animal cell cytokinesis
Plant cell cytokinesis
Stages of Cell plate formation
Potential Kinases Involved in Cytokinesis
Mutations affecting cell plate formation

3. Cytokinesis:
divides the cytoplasm of a parental cell into two daughter cells
separate the cell in half and ensure that one nucleus ends up in each daughter cell
starts during the nuclear division phase called anaphase and continues through telophase

4. Animal cell cytokinesis
The mitotic spindle defines the site at which cleavage furrow is formed.
A contractile ring containing actin and myosin is formed at this site.
Contraction of this ring creates a furrow that pulls the overlying plasma membrane
A transient structure, the midbody is formed.
The common membrane that surrounds the cell increases in surface area and divides the two daughter cells

5. Timing cytokinesis
must be temporally controlled to ensure that it occurs only after sister chromatids separate during the anaphase
Cytokinesis happens only after APC binds with CDC20
allowing for the separation of chromosomes and myosin to work simultaneously

6. Plant cell cytokinesis
Cytokinesis is more complex in plants than in animals
Presence of Cell wall
Absence of Cell migration
Rather than forming a contractile ring, plant cells construct a cell plate in the middle of the cell

7. Key terms:
Cell plate: a disk-like, membrane-bound structure, laid down in the center of the phragmoplast
Phragmoplast : a loose cytoskeletal structure held together by two arrays of microtubule bundles and also contains actin
Phragmoplastin :a dynamin-like protein, which is associated with the cell plate vesicles

8. The Preprophase Band
The PPB is laid down prior to the commencement of cell division, thereby marking the future site of the cell plate.
Determines the division site .
Influences cell polarity and formation of the mitotic spindle.
May involve cyclin-dependent kinases.
Cortical actin filaments appear to play a critical role in positioning and fixing the site of the PPB.

9. Stages of Cell plate formation
The transport and arrival of Golgi-derived vesicles to the equatorial region of the cell
The formation of the tubulovesicular network (TVN)
Consolidation of TVN into a smooth tubular network and fenestrated plate-like structure filled with callose
Fusion of the margin of the cell plate with the parental cell membrane
Synthesis of cellulose and the maturation of the cell plate into the cell wall

10. Phragmoplastin, a Marker for the Phragmoplast and Initiation of the Cell Plate
Immunofluorescence microscopy localized this protein to the cell plate in dividing soybean root tip cells
Phragmoplastin is located across the newly formed cell plate, with a higher concentration at the ends where vesicle fusion is most active.
Once the cell plate is completed, phragmoplastin disappears.
Function:
to create VTV structures at the forming cell plate

11. Localization of phragmoplastin

12. Potential Kinases Involved in Cytokinesis
The initiation of cytokinesis requires inactivation of CDK1
The colocalization of Cdc2 kinase with three microtubular structures, the PPB, the spindle, and the cell plate
Polo kinase( in yeast and animals) Promotes CDK1 inactivation
A Nicotiana protein kinase 1 (NPK1), which is related to MAPK3, is activated by NPK1-activating kinesin-like protein (NACK1) NPK1 and NACK1 are localized to the equatorial region of the phragmoplast
MAP kinase, p43Ntf6, showed activity only in dividing cells and appears to localize at the cell plate

13. Role of KNOLLE

14. Synthesis of callose and cellulose during cell plate formation
accumulate as TVN is established.
detected at the T junction of the parental cell wall
Cellulose:
detected as the plate begins to mature and fuse with the parental plasma membrane
(A) Callose, labeled with a monoclonal antibody to callose, is synthesized in the forming cell plate and in parts of the parental cell wall at the T-junction. (B) Cellulose, labeled with cellobiohydrolase I-gold, begins to be synthesized when the cell plate fuses with the parental cell wall

15. Mutations affecting cell plate formation
cyt1 mutant: the absence of cellulose biosynthesis causes incomplete cell walls and excessive callose accumulation without forming cellulose
Overexpression of phragmoplastin also causes accumulation of callose, which appears to delay cell wall maturation
keulle mutant of Arabidopsis: multinucleate cells with incomplete cell plates are formed (The keulle gene product apparently functions downstream of KNOLLE, and keulle protein may interact with KNOLLE)
The GNOM gene affects the position of cell plate and pattern formation

16. Future Prospects
Identification and understanding of the role of proteins in imprinting the division site marked by PPB during the G2 phase of cell cycle is of paramount importance
Further genetic studies on plant mutations affecting cell plate formation, position, orientation and size of cells, and the use of double mutations in combination with molecular studies may allow us to decipher the function of various genes in cytokinesis and cell plate formation in plants.

17. References: Annu. Rev. Plant Physiol. Plant Mol. Biol. 2001. 52:751–84
"Cytokinesis." Nature.com. Nature Publishing Group, n.d. Web. 17 Jan
Geisler-Lee, C.jane, Zonglie Hong, and Desh Pal S Verma. "Overexpression of the Cell Plate-associated Dynamin-like GTPase, Phragmoplastin, Results in the Accumulation of Callose at the Cell Plate and Arrest of Plant Growth." Plant Science (2002): Web.
Wilson, John H., and Tim Hunt. Molecular Biology of the Cell, 4th Edition: A Problems Approach. New York: Garland Science, Print.