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Transcript
Cytokinesis and Cell plate
PCDU seminar winter term 2015/16
Nabila Riaz
1
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
2
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
3
Animal cell cytokinesis
1.
2.
3.
4.
5.
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
4
Timing cytokinesis
1. must be temporally controlled to ensure that it occurs only
after sister chromatids separate during the anaphase
2. Cytokinesis happens only after APC binds with CDC20
3. allowing for the separation of chromosomes and myosin to
work simultaneously
5
Plant cell cytokinesis
Absence of
Cell
migration
Presence of
Cell wall
Cytokinesis is
more complex
in plants than in
animals
Rather than forming a contractile ring, plant cells
construct a cell plate in the middle of the cell
6
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
7
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.
8
Stages of Cell plate formation
1. The transport and arrival of Golgi-derived vesicles to the
equatorial region of the cell
2. The formation of the tubulovesicular network (TVN)
3. Consolidation of TVN into a smooth tubular network and
fenestrated plate-like structure filled with callose
4. Fusion of the margin of the cell plate with the parental cell
membrane
5. Synthesis of cellulose and the maturation of the cell plate
into the cell wall
9
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:
1. to create VTV structures at the forming cell plate
10
Localization of phragmoplastin
11
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
12
Role of KNOLLE
13
Synthesis of callose and cellulose during cell plate
formation
1.
•
•
2.
•
Callose :
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 14
be
synthesized when the cell plate fuses with the parental cell wall
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
15
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.
16
References:
• Annu. Rev. Plant Physiol. Plant Mol. Biol. 2001. 52:751–84
• "Cytokinesis." Nature.com. Nature Publishing Group, n.d. Web. 17 Jan.
2016.
• 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 163.1 (2002): 33-42. Web.
• Wilson, John H., and Tim Hunt. Molecular Biology of the Cell, 4th Edition: A
Problems Approach. New York: Garland Science, 2002. Print.
• http://hubpages.com/education/The-Cell-Cycle
• https://en.wikipedia.org/wiki/Preprophase_band
• https://en.wikipedia.org/wiki/Cytokinesis
17
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