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Expansion of the phragmoplast during plant cytokinesis:
a MAPK pathway may MAP it out
Ryuichi Nishihama* and Yasunori Machida†
Plant cytokinesis involves the formation of a cell plate. This is details of cell-plate maturation have been revealed through accomplished with the help of the phragmoplast, a plant- the observation of cryofixed tobacco cells by Samuels et al. specific cytokinetic apparatus that consists of microtubules [5] (Figure 1a). Vesicles fuse via long thin (i.e. 20 nm in and microfilaments. During centrifugal growth of the cell plate, diameter) curving fusion tubes to produce a fusion-tube- the phragmoplast expands to keep its microtubules at the generated membrane network (FTN). This network leading edge of the cell plate. Recent studies have revealed undergoes a series of morphological and biochemical potential regulators of phragmoplast microtubule dynamics changes, including the formation of a tubulo-vesicular and the involvement of a mitogen-activated protein kinase network (TVN), a tubular network (TN), and a fenestrated cascade in the control of phragmoplast expansion. These membrane sheet. The cell plate grows centrifugally, studies provide new insights into the molecular mechanisms through the continuous addition of vesicles to its edge, until of plant cytokinesis.
it reaches the parental cell walls. Therefore, the center ofthe growing cell plate is the most mature part.
*Department of Biology, University of North Carolina, Chapel Hill,
The apparatus responsible for localization and fusion of North Carolina 27599-3280, USA vesicles is the phragmoplast, whose formation is initiated † Developmental Biology Group, Division of Biological Science, during late anaphase [1]. A phragmoplast complex is com- Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku,Nagoya 464-8602, Japan; e-mail: [email protected] posed of two bundles of anti-parallel microtubules (MTs) Correspondence: Yasunori Machida and actin filaments. MTs are, in general, orientated andconsist of a plus end and a minus end. The MTs overlap at Current Opinion in Plant Biology 2001, 4:507–512
their plus ends in the center of the phragmoplast. The 1369-5266/01/$ — see front matter initial shape of the phragmoplast is a cylinder- or barrel- 2001 Elsevier Science Ltd. All rights reserved.
like structure. Golgi-derived vesicles are transported to the equator of the phragmoplast by the MTs, whose action is Anaphase spindle elongation1 probably assisted by MT motor proteins that have yet to Arabidopsis thaliana phragmoplast-associated be identified [6]. Once cell-plate formation begins in its kinesin-related protein 1 equatorial zone, the phragmoplast changes into a ring-like structure and centrifugally expands, maintaining localiza- cyclin-dependent kinase tion of the MTs at the leading edge of the cell plate. This Daucus carota kinesin-related protein of 120 kDa-2 change in phragmoplast shape is crucial for the lateral fusion-tube-generated membrane network growth of the cell plate. This review focuses on the mech- kinesin-like MT-based motor protein MT-associated protein anism of lateral expansion of the phragmoplast and mitogen-activated protein kinase encompasses recent findings that shed light on the regula- tion of this process. For aspects of cytokinesis not covered in this review, such as mechanisms of vesicle fusion, roles of actin filaments, and control of the division plane, the nucleus- and phragmoplast-localized protein kinase1 Nicotiana tabacum MAPK 6 reader is referred to other recent review articles [7–10].
Nicotiana tabacum MAP65-1 Protein Regulator of Cytokinesis1 Phragmoplast expansion driven by
tobacco kinesin-related polypeptide of 125 kDa MT turnovers
tubulo-vesicular network How do phragmoplast MTs move centrifugally toward thecortex as the cell plate grows? A clue came from an exper- iment performed by Yasuhara et al. [6] who used taxol, a Cytokinesis is a physical process that distributes genetic chemical that blocks depolymerization of MTs, to examine information and cytoplasm from a parent cell into two the mechanism of cell-plate expansion. Taxol treatment of daughter cells. In higher plants, cytokinesis is achieved tobacco bright yellow-2 (BY-2) cultured cells during through the formation of a new cross-wall, called the cell telophase inhibits the centrifugal expansion of their plate, which stretches from the interior to the periphery of phragmoplasts, producing cells with abnormally thick cell the cell [1]. Materials for the construction of the cell plate plates that apparently result from the increased accumula- are supplied from the Golgi complex through the vesicle tion of vesicles (Figure 1d). The requirement for MT trafficking system [2,3•,4•]. Membrane vesicles that have depolymerization during phragmoplast expansion indicates budded from the Golgi fuse with one another to form an that neither the pushing force of the cell plate nor the immature cell plate between the two daughter nuclei. The pulling force of the parental cell walls is responsible for the Cell biology
Diagram of phragmoplast expansion and (b) Brefeldin A treatment
cell-plate formation in normal, drug-treated, or
genetically modified plant cells. (a) In a normal
plant cell, a phragmoplast is assembled with
anti-parallel MTs overlapping in the center attheir plus ends (+). Fusion of Golgi-derivedvesicles (open circles), through fusion tubes in the equatorial zone of the phragmoplast, gives rise to a FTN (orange), whichsuccessively maturates into a TVN (red), a TN (pink), and a fenestrated sheet/cell plate (blue). In (a), green bars represent MTs that (c) Caffeine treatment
have recently been polymerized, or in (b,c),
that are not yet destined for depolymerization,
whereas gray bars represent MTs that are destined for depolymerization during the nextstage. Note that the shape of thephragmoplast changes during the transitionfrom a cylinder to a ring, which is marked byan asterisk. (b) Brefeldin A blocks the supplyof vesicles by disrupting the Golgi, resulting ina lack of cell-plate materials in thephragmoplast equator. (c) Caffeine blocks thematuration of the FTN into the TVN, which eventually results in the collapse of the FTN.
(d) Taxol blocks the depolymerization of MTs,
which inhibits phragmoplast expansion but
(d) Taxol treatment or
allows the formation of an incomplete cell kinase-negative NPK1 plate. Overexpression of a kinase-negative mutant of the NPK1 MAPKKK results in asimilar phenotype. Note that, in (b−d),phragmoplasts are never transformed intoring shapes.
incomplete cell plate Current Opinion in Plant Biology mechanical enlargement of the phragmoplast. Rather, it fluorescein-labeled tubulins, Hush et al. [13] observed a seems more likely that the supply of free tubulins, which rapid and uniform recovery of fluorescence. This observa- have been depolymerized from preexisting MTs on the tion is more consistent with a mechanism of dynamic inner side of the phragmoplast, forces the lateral expansion instability and exchange of tubulin dimers than with of the phragmoplast by constructing new MT arrays at its treadmilling. Therefore, depolymerization of MTs might outer edge. Thus, the phragmoplast appears to possess an also occur at the plus end of MTs in the phragmoplast. If activity that can initiate MT polymerization at its outer edge.
this were the case, then MTs on the inner side of thephragmoplast would be more unstable than those on the The incorporation of free tubulins into the phragmoplast is known to occur at the plus ends of MTs located in theequatorial zone [11,12]. On the basis of the fluorescence Phragmoplast MT-associated proteins (MAPs)
redistribution after photobleaching (FRAP) analysis per- Recently, two classes of MT-associated proteins (MAPs), formed by Hush et al. [13], phragmoplast MTs seem to which are possible regulators of MT dynamics, have been exhibit dynamic instability [14]. Following the photo- shown to localize to the phragmoplast. One of these classes bleaching of phragmoplast MTs that had incorporated is comprised of the kinesin-like MT-based motor proteins Expansion of the phragmoplast during plant cytokinesis Nishihama and Machida 509
(KLPs). Plus-end-directed KLPs, including Xenopus kinesin characteristic sequences. Our computer-based analysis also central motor1 (XKCM1) [15] and Xenopus kinesin predicted that NtMAP65-1 proteins may form a highly superfamily2 (XKIF2) [16], and the minus end-directed α-helical structure similar to that of PRC1 (R Nishihama, KLP KAR3 [17] are known to depolymerize MTs at the Y Machida, unpublished data).
plus and minus end, respectively (reviewed in [18]).
Arabidopsis thaliana phragmoplast-associated kinesin- After anaphase, PRC1 is restricted to plus-end MT-over- related protein1 (AtPAKRP1) is localized to the center of lapping regions [25], a pattern that is reminiscent of the phragmoplast, and microinjection of anti-AtPAKRP1 NtMAP65-1 localization in plant cells. Remarkably, the antibodies or truncated AtPAKRP1 proteins into tobacco microinjection of anti-PRC1 antibodies into HeLa cells BY-2 cells leads to the disorganization of phragmoplast blocks the completion of cytokinesis [25]. Although it is MTs [19••]. Carrot DcKRP120-2 (Daucus carota kinesin- still unclear what PRC1 actually does to MTs, this study related protein of 120 kDa-2) is a KLP homologue of on PRC1 raises the possibility that NtMAP65-1 proteins tobacco TKRP125 (tobacco kinesin-related polypeptide of also control the progression of cytokinesis in plants by 125 kDa) [20•], which possesses an activity that translo- regulating phragmoplast-MT dynamics. Whether PRC1 cates phragmoplast MTs toward their minus ends.
and Ase1 actively promote MT polymerization is now an TKRP125 is localized to whole arrays of phragmoplast open question.
MTs except for their plus ends [21]. Unlike TKRP125,DcKRP120-2 is also localized to the MT-interdigitating Recent studies have revealed the existence of plant zone of the phragmoplast [20•]. The minus end-directed proteins in addition to the NtMAP65-1 family that have KLPs, KCBP (kinesin-like calmodulin-binding protein) [22] homologies to animal MAPs [28•,29•]. Furthermore, our and KatA (kinesin-like protein in Arabidopsis thaliana A) brief search of the complete Arabidopsis genome sequence [23], localize along the length of phragmoplast MTs. It will revealed two putative MAPs with similarity to human be intriguing to test the effects of these KLPs on MT dis- EB1 protein and MAP1A/B light chain 3 (R Nishihama, assembly. The roles of these KLPs in the progression of M Y Machida, unpublished data). Interestingly, EB1 is phase or the expansion of phragmoplasts remain unknown.
known to localize to MT plus ends and is involved in theregional control of MT dynamics and capture (see [30,31] Another MAP family is comprised of the structural MAPs for reviews). Further research should be performed to test recently identified by Smertenko et al. [24••]. They identi- the involvement of various MAPs in the regulation of fied a member of the tobacco NtMAP65-1 (Nicotiana phragmoplast MT dynamics.
tabacum MAP65-1) family that is able to bind to taxol-stabilized MTs. This MAP promotes polymerization of Co-ordination of phragmoplast expansion with
MTs in vitro but does not promote the bundling of MTs [24••]. This polymerizing activity is sufficient to classify As described above, expansion of the phragmoplast is the protein as a MT-dynamics regulator. Antiserum that essential for the lateral growth of the cell plate. Cell-plate recognizes multiple members of the NtMAP65-1 family formation and phragmoplast expansion are co-dependent: does not stain all MT arrays. At metaphase, the antiserum without formation of the cell plate the phragmoplast never stains an area of spindle MTs proximal to the metaphase expands. For example, the use of brefeldin A (BFA), a plate but not those at the pole [24••]. The antibody also chemical that disrupts the Golgi apparatus, to block the stains the spindle midzone and the phragmoplast equator- supply of vesicles carrying cell-plate materials prevents the ial zone [24••]. These patterns of localization suggest a role formation of the cell plate and results in the generation of for NtMAP65-1 proteins in the regulation of MT dynamics binucleate cells [2], but does not disturb phragmoplast in specific areas of the spindle and the phragmoplast where formation [32]. Interestingly, under appropriate conditions, MTs overlap at their plus ends.
BFA treatment completely arrests the lateral expansion ofphragmoplasts at the cylindrical stage after only an initial It is intriguing to note that NtMAP65-1 proteins have slight enlargement [32] (Figure 1b). These phragmoplasts significant amino-acid-sequence homology to two other no longer become ring-shaped and no MT disassembly MAPs: human PRC1 (Protein Regulator of Cytokinesis1), takes place in their central region. Thus, the process of which is required for cytokinesis [25], and yeast Ase1 phragmoplast expansion is tightly linked to cell-plate (Anaphase spindle elongation1), which is required for formation. This finding suggests that there may be a spindle assembly, elongation and disassembly [26]. PRC1 mechanism that induces MT depolymerization in and Ase1 share two notable sequence features: a consensus response to cell-plate formation.
cyclin-dependent kinase (CDK) phosphorylation site anda sequence that is similar to a mitotic cyclin destruction What is the cue for MT depolymerization? Caffeine is box. It has been proven both in vivo and in vitro that PRC known to disrupt cell-plate formation in plants ([33] and is phosphorylated at the consensus CDK phosphorylation references therein). In Tradescantia stamen-hair cells treated sites by CDK2 [25]. It has also been proven that Ase1 is a with caffeine, cell-plate formation is initiated but the target of proteolysis mediated by the anaphase-promoting immature cell plate ceases to grow and is ultimately complex [27]. NtMAP65-1 proteins also exhibit these degraded after it has expanded to about three-quarters Cell biology
of the cell's width [34]. Although the initiation of the These findings suggest a role for NPK1 in cytokinesis.
phragmoplast is not inhibited in this system, the phrag- Indeed, inhibition of NPK1 signaling has been shown to moplast fails to adopt a ring structure and remains fixed result in a defect in cytokinesis [39••]. Overexpression of a as a cylindrical structure (Figure 1c). Electron microscopy kinase-negative mutant of NPK1 (NPK1KW) induces the of cryofixed BY-2 cells shows that caffeine disrupts the formation of multinucleate cells that contain incomplete conversion of the FTN into the TVN during the develop- disc-shaped cell plates. This mutant protein still localizes ment of the cell plate [33,35]. This implies that a minimal to the equator of the phragmoplast. The phragmoplast level of TVN formation is required for the induction of does not expand, however, in NPK1KW-overexpressing MT disassembly. Consistent with this finding, it has been plants (Figure 1d). Thus, NPK1 regulates the expansion of observed that phragmoplast MTs are associated with the both the cell plate and the phragmoplast.
TVN but not with the TN [5] (Figure 1a). Taken together,these results suggest that MT depolymerization is induced It should be noted that NPK1KW-induced incomplete cell during the TVN→TN transition. An ultrastructural study plates that are formed in NPK1KW-expressing cells con- has also revealed several features of the TVN, such as tain callose [39••], a polysaccharide whose synthesis is assembly of the fuzzy membrane coat, widening of the initiated at the TVN stage [5] (see above). Thus, it would connecting tubules, formation of clathrin-coated buds, and appear that NPK1 is primarily involved in a step that takes initiation of callose synthesis [5]. These features are good place after the formation of the TVN, that is, in the out- candidates for events that constitute ‘MT-disassembly ward redistribution of phragmoplast MTs. Consistent with signals'. In conclusion, cell-plate expansion is driven by this, the effect provoked by blocking NPK1 signaling is successive rounds of the following events: vesicle transport similar to that of taxol treatment (see above; Figure 1d).
to the phragmoplast equator, formation of the FTN by NPK1 might regulate MT depolymerization at plus ends vesicle fusion, maturation of the FTN into the TVN, and in response to MT-disassembly signals generated in the MT disassembly on the inside and its reassembly on the TVN/TN. There is, however, still a possibility that NPK1 outside of phragmoplast. might be involved in some of the earlier steps if inhibitionby the dominant-negative mutant were not complete.
A mitogen-activated protein kinase
(MAPK) cascade as a regulator of

The identification of downstream targets of NPK1 will be decisive in completing our understanding of the molecular A coupling mechanism should exist between the events mechanism of phragmoplast expansion. It will be intriguing involved in cell-plate formation and the disassembly of to examine whether NPK1 regulates the MAPs that are phragmoplast MTs. Recent studies have suggested the mentioned above and, if so, whether this regulation is involvement of a mitogen-activated protein kinase mediated directly by NPK1 or indirectly through a putative (MAPK) cascade in the regulation of such a coupling MAPK cascade initiated by NPK1. In light of this, it should mechanism [36–38,39••]. The MAPK cascade is a signaling be noted that the p43Ntf6 MAPK from tobacco [36] and pathway that is conserved in all eukaryotes and that alfalfa MMK3 (Medicago MAPK3) [37] are activated during consists of members of three protein kinase families. In cytokinesis. Both of these proteins are localized to the their respective order in the signaling cascade, they are the equatorial zone of the phragmoplast, and MMK3 is also MAPK kinase kinase (MAPKKK) family, the MAPK localized to the cell plate. Most recently, a tobacco kinase (MAPKK) family and the MAPK family [40].
MAPKK, Nicotiana tabacum MAPK/extracellular signal-regulated protein kinase kinase (NtMEK1), that activates On the basis of the sites of its transcript accumulation, a p43Ntf6 has been identified as a possible component of a tobacco MAPKKK, Nucleus- and Phragmoplast-localized MAPK cascade involved in phragmoplast expansion [38], Protein kinase1 (NPK1) [41], has been suggested to play a although its sub-cellular localization remains to be deter- role in cell division [42]. The accumulation of NPK1 protein mined. Thus, phragmoplast expansion in tobacco may be is cell-cycle dependent; proteins are present in the cell regulated by a MAPK cascade, involving NPK1 MAPKKK, from S to M phase, with a peak in accumulation during NtMEK1 MAPKK and p43Ntf6 MAPK, although evidence Mphase, after which NPK1 is degraded [39••]. NPK1 is for the involvement of NtMEK1 and p43Ntf6 remains to confined to the nucleus from S phase to prophase [39••].
NPK1 kinase activity is transiently increased late in Mphase [39••]. Upon nuclear envelope breakdown, NPK1 In animal cells, active MAPKs have been shown to be proteins are dispersed into the cytoplasm and localize in localized to the spindle midzone and midbody, a cytokinetic patches until early anaphase. By late anaphase, NPK1 bridge composed of MTs [43,44]. Although direct evidence begins to concentrate at the spindle midzone before for the involvement of MAPKs in cytokinesis is still lack- becoming localized to the equatorial zone of the cylindrical ing, we speculate that animal MAPKs might also regulate phragmoplast. During cytokinesis, NPK1 is consistently MT dynamics. In animal cells, cytokinesis proceeds in an found at the equator of the ring-shaped phragmoplast, but outside-in mode by the constriction of the cortex.
not at the cell plate. Some NPK1 proteins relocate back to Therefore, spindle MTs must change their positions to the reforming daughter nuclei.
move inwardly during cortex constriction because the width Expansion of the phragmoplast during plant cytokinesis Nishihama and Machida 511
of the spindle is limited by the cortex. This redistribution Heese M, Mayer U, Jürgens G: Cytokinesis in flowering plants:
cellular process and developmental integration.
Curr Opin Plant
may involve MT turnovers. In addition, midbody MTs Biol 1998, 1:486-491.
should disassemble upon cell separation. Thus, the mech- Smith LG: Divide and conquer: cytokinesis in plant cells. Curr Opin
anism that regulates MT dynamics during cytokinesis may Plant Biol 1999, 2:447-453.
be conserved in plants and animals.
Nacry P, Mayer U, Jürgens G: Genetic dissection of cytokinesis.
Plant Mol Biol 2000, 43:719-733.
10. Verma DPS: Cytokinesis and building of the cell plate in plants.
In this review, we highlight the molecular mechanism for Annu Rev Plant Physiol Plant Mol Biol 2001, 52:751-784.
the expansion of the phragmoplast during plant cytokinesis.
11. Vantard M, Levilliers N, Hill AM, Adoutte A, Lambert AM: Incorporation of Paramecium axonemal tubulin into higher plant
Phragmoplast expansion is a process of repeated depoly- cells reveals functional sites of microtubule assembly. Proc Natl
merization and repolymerization, during which MT Acad Sci USA 1990, 87:8825-8829.
disassembly is linked to the progression of cell-plate 12. Asada T, Sonobe S, Shibaoka H: Microtubule translocation in the
formation. Changes in MT stability may be mediated by cytokinetic apparatus of cultured tobacco cells. Nature 1991,
MAPs, such as various KLPs and NtMAP65-1 proteins thatlocalize to the equator of the phragmoplast. The NPK1 13. Hush JM, Wadsworth P, Callaham DA, Hepler PK: Quantification
of microtubule dynamics in living plant cells using
MAPKKK, and probably a MAPK cascade initiated by fluorescence redistribution after photobleaching. J Cell Sci 1994,
NPK1, is involved in phragmoplast expansion. One of the possible functions of this pathway would be to regulate 14. Mitchison T, Kirschner M: Dynamic instability of microtubule
growth. Nature 1984, 312:237-242.
MT depolymerization in response to signals generated bythe forming cell plate. Further research in this field will 15. Walczak CE, Mitchison TJ, Desai A: XKCM1: a Xenopus kinesin-
related protein that regulates microtubule dynamics during
aim to elucidate the MT-disassembly signals, identify the mitotic spindle assembly. Cell 1996, 84:37-47.
target proteins of the MAPK pathway, and examine 16. Desai A, Verma S, Mitchison TJ, Walczak CE: Kin I kinesins are
whether MAP activities are spatially regulated at the inner microtubule-destabilizing enzymes. Cell 1999, 96:69-78.
and outer edges of the phragmoplast.
Endow SA, Kang SJ, Satterwhite LL, Rose MD, Skeen VP,
Salmon ED: Yeast Kar3 is a minus-end microtubule motor protein
that destabilizes microtubules preferentially at the minus ends.

EMBO J 1994, 13:2708-2713.
We thank Hiroki Yasuhara, Tetsuhiro Asada, and members of the Machidalaboratory for helpful discussion. Work performed by the authors was 18. Hunter AW, Wordeman L: How motor proteins influence
supported by Grants-in-Aid for Scientific Research on Priority Areas (Award microtubule polymerization dynamics. J Cell Sci 2000,
numbers 0678101-3 and 10182101-2) from the Japanese Ministry of Education, Science, Culture and Sports; and by a grant from the Research 19. Lee YR, Liu B: Identification of a phragmoplast-associated
for the Future Program of the Japan Society for the Promotion of Science.
kinesin-related protein in higher plants. Curr Biol 2000,
RN was supported by Research Fellowships from the Japan Society for the Promotion of Science for Young Scientists.
The cloning of AtPAKRP1 cDNA is reported. AtPAKRP is the first kinesin-like protein shown to be localized to the phragmoplast equator.
Microinjection of anti-AtPAKRP1 antibodies into BY-2 cells results in the dis- References and recommended reading
organization of the phragmoplast, implicating AtPAKRP1 involvement in Papers of particular interest, published within the annual period of review, phragmoplast MT assembly.
have been highlighted as: 20. Barroso C, Chan J, Allan V, Doonan J, Hussey P, Lloyd C: Two
• of special interest kinesin-related proteins associated with the cold-stable
•• of outstanding interest cytoskeleton of carrot cells: characterization of a novel kinesin,
Plant J 2000, 24:859-868.
Gunning BES: The cytokinetic apparatus: its development and
The authors report the biochemical purification of two proteins with kinesin- spatial regulation. In The Cytoskeleton in Plant Growth and
like properties from carrot, and the identification of one of them as Development. Edited by Lloyd CW. London: Academic Press; DcKRP120-2. The other purified protein is recognized by an anti-TKRP125 antibody. DcKRP120-2 is homologous to tobacco TKRP125 but, unlikeTKRP125, it is localized to the phragmoplast equator in some cells.
Yasuhara H, Sonobe S, Shibaoka H: Effects of brefeldin-A on the
formation of the cell plate in tobacco BY-2 cells.
Eur J Cell Biol
21. Asada T, Kuriyama R, Shibaoka H: TKRP125, a kinesin-related
protein involved in the centrosome-independent organization of
the cytokinetic apparatus in tobacco BY-2 cells.
J Cell Sci 1997,
Sonobe S, Nakayama N, Shimmen T, Sone Y: Intracellular
distribution of subcellular organelles revealed by antibody against
xyloglucan during cell cycle in tobacco BY-2 cells.
22. Bowser J, Reddy AS: Localization of a kinesin-like calmodulin-
binding protein in dividing cells of Arabidopsis and tobacco.
The authors of this paper report that xyloglucan, a polysaccharide that is Plant J 1997, 12:1429-1437.
used for the construction of the cell wall matrix, is transported from the Golgito the cell plate via the phragmoplast.
23. Liu B, Cyr RJ, Palevitz BA: A kinesin-like protein, KatAp, in the cells
of Arabidopsis and other plants. Plant Cell 1996, 8:119-132.
Yokoyama R, Nishitani K: Endoxyloglucan transferase is localized
both in the cell plate and in the secretory pathway destined for
24. Smertenko A, Saleh N, Igarashi H, Mori H, Hauser-Hahn I, Jiang CJ, the apoplast in tobacco cells. Plant Cell Physiol 2001, 42:292-300.
Sonobe S, Lloyd CW, Hussey PJ: A new class of microtubule-
Endoxyloglucan transferase, an enzyme responsible for forming and rear- associated proteins in plants. Nat Cell Biol 2000, 2:750-753.
ranging the cellulose-xyloglucan network of the cell wall, is shown to be The first cloning of the plant structural MAP genes NtMAP65-1a–c is transported from the Golgi to the cell plate via the phragmoplast.
reported. Recombinant NtMAP65-1a proteins stimulate MT polymerizationin vitro. The localization of NtMAP65-1 proteins to the phragmoplast equa- Samuels AL, Giddings TH Jr, Staehelin LA: Cytokinesis in tobacco
tor suggests that they are involved in the regulation of phragmoplast MT BY-2 and root tip cells: a new model of cell plate formation in
dynamics at the plus end.
higher plants. J Cell Biol 1995, 130:1345-1357.
25. Jiang W, Jimenez G, Wells NJ, Hope TJ, Wahl GM, Hunter T, Yasuhara H, Sonobe S, Shibaoka H: Effects of taxol on the
Fukunaga R: PRC1: a human mitotic spindle-associated CDK
development of the cell plate and of the phragmoplast in tobacco
substrate protein required for cytokinesis. Mol Cell 1998,
BY-2 cells. Plant Cell Physiol 1993, 34:21-29.
Cell biology
26. Pellman D, Bagget M, Tu YH, Fink GR, Tu H: Two microtubule-
36. Calderini O, Bögre L, Vicente O, Binarova P, Heberle-Bors E, associated proteins required for anaphase spindle movement in
Wilson C: A cell cycle regulated MAP kinase with a possible
Saccharomyces cerevisiae. J Cell Biol 1995, 130:1373-1385.
role in cytokinesis in tobacco cells. J Cell Sci 1998,
Juang YL, Huang J, Peters JM, McLaughlin ME, Tai CY, Pellman D:
APC-mediated proteolysis of Ase1 and the morphogenesis of the
Bögre L, Calderini O, Binarova P, Mattauch M, Till S, Kiegerl S, mitotic spindle. Science 1997, 275:1311-1314.
Jonak C, Pollaschek C, Barker P, Huskisson NS et al.: A MAP kinase
is activated late in plant mitosis and becomes localized to the

28. Smith LG, Gerttula SM, Han S, Levy J: Tangled1: a microtubule
plane of cell division. Plant Cell 1999, 11:101-113.
binding protein required for the spatial control of cytokinesis in
J Cell Biol 2001, 152:231-236.
38. Calderini O, Glab N, Bergounioux C, Heberle-Bors E, Wilson C: The tangled1 gene is involved in the orientation of cytoskeletal structures.
A novel tobacco mitogen-activated protein (MAP) kinase kinase,
The authors show that it encodes a protein that has a basic region that is NtMEK1, activates the cell cycle-regulated p43Ntf6 MAP kinase.
similar to those of vertebrate APC proteins, which bind to MTs. Tangled1 J Biol Chem 2001, 276:18139-18145.
protein binds to MTs in vitro and to mitotic and cytokinetic MT structuresin vivo.
39. Nishihama R, Ishikawa M, Araki S, Soyano T, Asada T, Machida Y: The NPK1 mitogen-activated protein kinase kinase kinase is a
29. Whittington AT, Vugrek O, Wei KJ, Hasenbein NG, Sugimoto K, regulator of cell-plate formation in plant cytokinesis. Genes Dev
Rashbrooke MC, Wasteneys GO: MOR1 is essential for organizing
cortical microtubules in plants. Nature 2001, 411:610-613.
Cell-biological and reverse-genetic analyses reveal the involvement of the Temperature-sensitive (ts) mutations in the MICROTUBULE ORGANIZA- NPK1 MAPKKK in cell-plate formation. NPK1 is localized to the phragmo- TION 1 (MOR1) gene result in the disruption of cortical MTs at the plast equator. Overexpression of a kinase-negative NPK1 inhibits phragmo- restrictive temperature. Cloning of MOR1 revealed it to encode a HEAT- plast expansion, resulting in the formation of incomplete cell plates.
domain-containing protein that is homologous to animal MAPs includingXenopus XMAP215 and human TOGp, which regulate MT dynamics during 40. English J, Pearson G, Wilsbacher J, Swantek J, Karandikar M, Xu S, mitosis. It would be interesting to test MOR1 involvement in the regulation Cobb MH: New insights into the control of MAP kinase pathways.
of phragmoplast MT dynamics, although ts mutations do not affect mitotic Exp Cell Res 1999, 253:255-270.
and cytokinetic MT arrays.
41. Banno H, Hirano K, Nakamura T, Irie K, Nomoto S, Matsumoto K, 30. Tirnauer JS, Bierer BE: EB1 proteins regulate microtubule
Machida Y: NPK1, a tobacco gene that encodes a protein with a
dynamics, cell polarity, and chromosome stability. J Cell Biol
domain homologous to yeast BCK1, STE11, and Byr2 protein
kinases. Mol Cell Biol 1993, 13:4745-4752.
31. Schuyler SC, Pellman D: Microtubule ‘plus-end-tracking proteins':
42. Nakashima M, Hirano K, Nakashima S, Banno H, Nishihama R, the end is just the beginning. Cell 2001, 105:421-424.
Machida Y: The expression pattern of the gene for NPK1 protein
kinase related to mitogen-activated protein kinase kinase kinase

32. Yasuhara H, Shibaoka H: Inhibition of cell-plate formation by brefeldin
(MAPKKK) in a tobacco plant: correlation with cell proliferation.
A inhibited the depolymerization of microtubules in the central
Plant Cell Physiol 1998, 39:690-700.
region of the phragmoplast. Plant Cell Physiol 2000, 41:300-310.
33. Samuels AL, Staehelin LA: Caffeine inhibits cell plate formation by
43. Shapiro PS, Vaisberg E, Hunt AJ, Tolwinski NS, Whalen AM, disrupting membrane reorganization just after the vesicle fusion
McIntosh JR, Ahn NG: Activation of the MKK/ERK pathway during
step. Protoplasma 1996, 195:144-155.
somatic cell mitosis: direct interactions of active ERK with
kinetochores and regulation of the mitotic 3F3/2 phosphoantigen.

34. Valster AH, Hepler PK: Caffeine inhibition of cytokinesis: effect on
J Cell Biol 1998, 142:1533-1545.
the phragmoplast cytoskeleton in living Tradescantia stamen hair
Protoplasma 1997, 196:155-166.
44. Zecevic M, Catling AD, Eblen ST, Renzi L, Hittle JC, Yen TJ, Gorbsky GJ, Weber MJ: Active MAP kinase in mitosis: localization
35. Staehelin LA, Hepler PK: Cytokinesis in higher plants. Cell 1996,
at kinetochores and association with the motor protein CENP-E.
J Cell Biol 1998, 142:1547-1558.


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