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

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

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

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

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

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

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

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.

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

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

Localization of phragmoplastin

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

Role of KNOLLE

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

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

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.

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