MAPK级联途径调控植物细胞胞质分裂

胞质分裂(cytokinesis)是细胞分裂的最后关键一步,产生2个含有完整的遗传物质和胞质细胞器的子细胞．植物胞质分裂包括细胞板的形成,这一过程是在成膜体的牵引下由一些植物特有的步骤完成的．促分裂原活化蛋白激酶(MAPK)级联途径在真核生物中是高度保守的,由MAPKs,MAPKKs,MAPKKKs组成,通过MAPKKK→ MAPKK → MAPK的逐级磷酸化传递细胞信号．近来的研究表明, NACK-MAPKKK→MAPKK→MAPK→MAP65构成的信号途径调控植物细胞的胞质分裂．本文就这一信号途径,总结了植物胞质分裂机制的研究进展,并对其中的问题进行了讨论与展望．     

朱顶红生殖细胞胞质分裂的两种方式

大多数植物以形成细胞板方式完成胞质分裂过程,也有些植物以类似于动物和单细胞植物在赤道区形成收缩沟的方式而分成两部分。本工作应用电镜对朱顶红体外萌发9-18小时花粉管中的生殖细胞胞质分裂进行了研究。结果表明：70％的细胞表现的是第一种方式,30％却是第二种方式。即：朱硕红生殖细胞胞质分裂同时存在两种方式。前者最初以细胞板亚单位的形式出现于有丝分裂晚后期,它们聚集于成膜体的中央区域并于分裂末期融合成一个大的连续的单位(Fig．1-3)。大量新的微管形成于两组染色体之间(Fig．1)。分裂末期,细胞板形成并具胞质通道(Fig.2)。成膜体微管规则排列并穿过胞质通道向新形成的末期核伸展(Fig.2＆3)。这些微管与构成细胞板的质膜紧密联系(Fig．3)。后者则在有丝分裂后期开始(Fig．4),当两群染色体彼此分离时,生殖细胞质膜在中央区由两侧向内凹陷形成收缩沟。有时生殖细胞几乎被收缩沟分成两个部分(Fig．6)。发生缢缩的细胞中细胞器与具细胞板的无差异,但微管稀少并且排列紊乱(Fig．4＆5),染色体的状态使得难以准确区分细胞分裂时期。而且核膜的形成似乎始于有丝分裂后期、出现于染色体边缘(Fig.7)。有时尚有落后染色体出现(Fig.8)。据此认为：收缩沟的发生与核膜的重建、染色体的异常行为及微管无序有关。朱顶红生殖细胞同时存在两种方式的胞质分裂现象相当特殊,可能存在着两种胞质分裂机制。由于游离的生殖细胞在某种程度上类似于动物细胞,因而以缢缩方式完成胞质分裂是可能的。另一方面,生殖细胞对花粉管生长所处的环境极为敏感,体外培养造成生殖细胞不规剧分裂的可能性也应考虑。因此研究在柱头上萌发花粉管中的生殖细胞的胞质分裂是有意义的,此研究结果将有助于更好地理解生殖细胞胞质分裂的机制。     

朱顶红生殖细胞胞质分裂的两种方式(英文)

大多数植物以形成细胞权方式完成胞质分裂过程,也有些植物以类似于动物和单细胞植物在赤道区形成收缩沟的方式而分成两部分。本工作应用电镜对朱顶红体外萌发９～１８小时花粉管中的生殖细胞胞质分裂进行了研究。结果表明：７０％的细胞表现的是第一种方式、３０％却是第二种方式。即：朱顶红生殖细胞胞质分裂同时存在两种方式。前者最初以细胞板亚单位的形式出现于有丝分裂晚后期,它们聚集于成膜体的中央区域并于分裂末期融合成一个大的连续的单位（Ｆｉｇ．１～３）。大量新的微管形成于两组染色体之间（Ｆｉｇ．１）。分裂末期,细胞板形成并具胞质通道（Ｆｉｇ．２）。成膜体微管规则排列并穿过胞质通道向新形成的末期核伸展（Ｆｉｇ．２＆３）。这些微管与构成细胞板的质膜紧密联系（Ｆｉｇ．３）。后者则在有丝分裂后期开始（Ｆｉｇ．４）,当两群染色体彼此分离时,生殖细胞质膜在中央区由两侧向内凹陷形成收缩沟。有时生殖细胞几乎被收缩沟分成两个部分（Ｆｉｇ．６）。发生缢缩的细胞中细胞器与具细胞板的无差异,但微管稀少并且排列紊乱（Ｆｉｇ．４＆５）,染色体的状态使得难以准确区分细胞分裂时期。而且核膜的形成似乎始于有丝分裂后期、出现于染色体边缘（Ｆｉｇ．７）。有时尚有落后     

细胞有丝分裂的胞质分裂

细胞有丝分裂通常包括核分裂(karyokinesis)及胞质分裂(cytokinesis)两个方面。两者虽有一定的关系,但核分裂并不一定随之有胞质分裂,结果形成双核或多核细胞,如多核原生动物及合胞体组织。因此,应将两者的分裂机制分别理解。关于核分裂机制,在所有细胞中是十分相似的,一般的认识也比较一致。在胞质分裂方面,存在许多不同的看法。大致在动物细胞     

esiRNA分析人源驱动蛋白MKLP1在胞质分裂中的功能

为探讨人源驱动蛋白MKLP1在有丝分裂和胞质分裂中的作用,以E.coliRNaseⅢ制备MKLP1的3′UTResiRNA转染HeLa细胞,通过定量RTPCR、Western印迹检测MKLP1esiRNA对MKLP1基因的沉默效率.再利用FACS分析、免疫荧光染色和活细胞成像分析检测MKLP1表达缺失后在有丝分裂和胞质分裂不同时期的细胞形态学、细胞分裂指数、细胞百分数,动态观察有丝分裂和胞质分裂期间的表型改变,以系统分析MKLP1的功能.最后通过挽救实验验证MKLP1esiRNA的作用特异性.实验显示MKLP1esiRNA转染HeLa细胞能够有效地特异性消除MKLP1的表达,并被异位表达的MKLP1所挽救.MKLP1蛋白在有丝分裂后期和末期前期位于纺锤体中间带,在末期后期和胞质分裂的最后阶段集中于中间体的中心处.MKLP1表达缺失使中间体正确形成和胞质分裂的完成受到严重抑制,造成大量双多核细胞堆积.结果表明,MKLP1在胞质分裂中间体形成和有丝分裂末期前期向后期过渡过程中起关键作用,是纺锤体中间体中间带相关蛋白,为胞质分裂所必需.     

植物的细胞分裂

細胞分裂是生物有机体普遍具有的特性。新个体的形成、幼年植物或动物的成長,主要通过细胞分裂,增加细胞的数目来完成的,因此細胞分裂可以說是实現生物体所特有的复制自己的特性的方式。植物在生長时期很容易看到細胞分裂,象有花植物的莖尖和根尖部分,細胞分裂經常在进行着。由于細胞分裂在个体形成和生長的重要性和出現的普遍性,不能不引超生物学者的重視,特别是在发現細胞分裂与生物的性狀遺傳有关以后,更加吸引細胞学家和遺傳学家对細胞分裂研究的兴趣。虽然,細胞     

似金隐藻有丝分裂及胞质分裂的观察

似金隐藻(Cryptomonas chrysoidea)是从青岛附近渤海湾海水中分离得到的一种单细胞藻类。对它的胞质分裂和有丝分裂进行的观察表明,它的胞质分裂在有丝分裂的中期开始,细胞前端沟口处先开始分裂,继而沿纵轴纵沟处形成一收缩沟完成的。似金隐藻的有丝分裂过程中没有染色体和着丝点形成;核膜进入中期时完全消失,纺锤体呈桶状,微管通过染色质团中的通道或直接与染色质团块相联;在后期和末期,两块分开的染色质团十分靠近相应的色素体内质网膜。本文对其分裂过程进行了讨论。     

应用胞质分裂阻滞法研究乙双吗啉对人淋巴细胞微核形成与增殖动力学的效应

乙双吗啉为我国首先合成的抗癌药,长期服用可诱发白血病,为进一步研究其遗传毒性的机理,本研究应用胞质分裂阻滞法（CB法）研究了乙双吗啉对体外培养人淋巴细胞微核形成及细胞动力学的效应。试验结果表明,乙双吗啉在胞质分裂阻滞的双核细胞及未阻滞的单核细胞中,均诱发微核形成并呈剂量依赖性增加;同时乙双吗啉具有明显的细胞毒性,抑制细胞分裂,双核与多核细胞率呈现剂量依赖性下降,可见,乙双吗啉是一个诱变与细胞毒因子。同时本文还讨论了CB-MNT实用价值的问题。     

微丝在卵子极性产生、分裂沟形成和极体排放中的作用

小鼠生发泡（ＧＶ）期卵母细胞在１μｇ／ｍｌ细胞松弛素Ｂ（ＣＢ）中培养,部分微丝解聚,卵母细胞不 能产生极性而在细胞中部形成分裂沟（假分裂）;极泡期印在１μｇ／ｍｌ ＣＢ中,分裂沟继续收缩,排放第 一极体。假分裂的分裂沟和极泡期的极区分裂沟形成均与分裂器中体位置相关。部分微丝解聚并不影响 假分裂和第一极体排放;全部微丝解聚（１０μｇ／ｍｌ ＣＢ）将中断假分裂和胞质分裂,分裂沟消失,卵恢 复球形。由此可见,成熟过程中卵母细胞极性的产生及分裂沟的形成都依赖于微丝的聚合。胞质分裂和 第一极体排放同样需一定量的微丝存在。     

胡杨小孢子发生及微管骨架变化与异常研究

利用压片法和间接免疫荧光结合DAPI(4′,6-diamidino-2-phenylindole)染色法,对胡杨小孢子母细胞减数分裂过程中微管骨架变化和染色体行为进行观察研究。结果表明:（1）胡杨小胞子母细胞减数分裂进程中染色体行为正常,其中:偶线期可观察到单价体,中期Ⅰ会出现落后染色体,末期Ⅰ和末期Ⅱ的核仁呈现动态变化。（2）胡杨小孢子发生过程中细胞内微管骨架呈动态变化过程,其中:中期Ⅱ形成平行纺锤体以及三极纺锤体;末期Ⅱ未观察到典型的成膜体结构,同时型胞质分裂受子核间辐射微管系统调节,通过胞质向心收缩而发生,胞质分裂后形成四边形和四面体型四分体。（3）胡杨小孢子母细胞减数分裂过程中还存在各种异常细胞学现象,其中:中期Ⅱ平行纺锤体发生融合;中期Ⅱ 和后期Ⅱ孢母细胞两个纺锤体间的胞质会出现裂沟;四分体时期存在三分体和二分体,并产生天然2n花粉和连体花粉。     

Cytokinesis in plant and animal cells: endosomes 'shut the door'

For many years, cytokinesis in eukaryotic cells was considered to be a process that took a variety of forms. This is rather surprising in the face of an apparently conservative mitosis. Animal cytokinesis was described as a process based on an actomyosin-based contractile ring, assembling, and acting at the cell periphery. In contrast, cytokinesis of plant cells was viewed as the centrifugal generation of a new cell wall by fusion of Golgi apparatus-derived vesicles. However, recent advances in animal and plant cell biology have revealed that many features formerly considered as plant-specific are, in fact, valid also for cytokinetic animal cells. For example, vesicular trafficking has turned out to be important not only for plant but also for animal cytokinesis. Moreover, the terminal phase of animal cytokinesis based on midbody microtubule activity resembles plant cytokinesis in that interdigitating microtubules play a decisive role in the recruitment of cytokinetic vesicles and directing them towards the cytokinetic spaces which need to be plugged by fusing endosomes. Presently, we are approaching another turning point which brings cytokinesis in plant and animal cells even closer. As an unexpected twist, new studies reveal that both plant and animal cytokinesis is driven not so much by Golgi-derived vesicles but rather by homotypically and heterotypically fusing endosomes. These are generated from cytokinetic cortical sites defined by preprophase microtubules and contractile actomyosin ring, which induce local endocytosis of both the plasma membrane and cell wall material. Finally, plant and animal cytokinesis meet together at the physical separation of daughter cells despite obvious differences in their preparatory events.     

Plant cytokinesis requires de novo secretory trafficking but not endocytosis

During plant cytokinesis membrane vesicles are efficiently delivered to the cell-division plane, where they fuse with one another to form a laterally expanding cell plate. These membrane vesicles were generally believed to originate from Golgi stacks. Recently, however, it was proposed that endocytosis contributes substantially to cell-plate formation. To determine the relative contributions of secretory and endocytic traffic to cytokinesis, we specifically inhibited either or both trafficking pathways in Arabidopsis. Blocking traffic to the division plane after the two pathways had converged at the trans-Golgi network disrupted cytokinesis and resulted in binucleate cells, whereas impairment of endocytosis alone did not interfere with cytokinesis. By contrast, inhibiting ER-Golgi traffic by eliminating the relevant BFA-resistant ARF-GEF caused retention of newly synthesized proteins, such as the cytokinesis-specific syntaxin KNOLLE in the ER, and prevented the formation of the partitioning membrane. Our results suggest that during plant cytokinesis, unlike animal cytokinesis, protein secretion is absolutely essential, whereas endocytosis is not.     

Characterization of AtCDC48. Evidence for multiple membrane fusion mechanisms at the plane of cell division in plants

The components of the cellular machinery that accomplish the various complex and dynamic membrane fusion events that occur at the division plane during plant cytokinesis, including assembly of the cell plate, are not fully understood. The most well-characterized component, KNOLLE, a cell plate-specific soluble N-ethylmaleimide-sensitive fusion protein (NSF)-attachment protein receptor (SNARE), is a membrane fusion machine component required for plant cytokinesis. Here, we show the plant ortholog of Cdc48p/p97, AtCDC48, colocalizes at the division plane in dividing Arabidopsis cells with KNOLLE and another SNARE, the plant ortholog of syntaxin 5, SYP31. In contrast to KNOLLE, SYP31 resides in defined punctate membrane structures during interphase and is targeted during cytokinesis to the division plane. In vitro-binding studies demonstrate that AtCDC48 specifically interacts in an ATP-dependent manner with SYP31 but not with KNOLLE. In contrast, we show that KNOLLE assembles in vitro into a large approximately 20S complex in an Sec18p/NSF-dependent manner. These results suggest that there are at least two distinct membrane fusion pathways involving Cdc48p/p97 and Sec18p/NSF that operate at the division plane to mediate plant cytokinesis. Models for the role of AtCDC48 and SYP31 at the division plane will be discussed.     

Feed-back regulation of successive meiotic cytokinesis

The paper considers a number of abnormal phenotypes with impaired temporal regulation of cytokinesis during the meiotic division of pollen mother cells. The phenomenon of “non-stop” cytokinesis with blocked arrest of the phragmoplast centrifugal motion and cell plate growth as well as incomplete and premature cytokinesis are described. The obtained data suggested a model for regulation of the processes involved in the arrest of the main cytokinesis processes during its completion in the plant meiosis.     

Control of plant cytokinesis by an NPK1-mediated mitogen-activated protein kinase cascade

Cytokinesis is the last essential step in the distribution of genetic information to daughter cells and partition of the cytoplasm. In plant cells, various proteins have been found in the phragmoplast, which corresponds to the cytokinetic apparatus, and in the cell plate, which corresponds to a new cross wall, but our understanding of the functions of these proteins in cytokinesis remains incomplete. Reverse genetic analysis of NPK1 MAPKKK (nucleus- and phragmoplast-localized protein kinase 1 mitogen-activated protein kinase kinase kinase) and investigations of factors that might be functionally related to NPK1 have helped to clarify new aspects of the mechanisms of cytokinesis in plant cells. In this review, we summarize the evidence for the involvement of NPK1 in cytokinesis. We also describe the characteristics of a kinesin-like protein and the homologue of a mitogen-activated protein kinase that we identified recently, and we discuss possible relationships among these proteins in cytokinesis.     

Membrane traffic: a driving force in cytokinesis

Dividing animal and plant cells maintain a constant chromosome content through temporally separated rounds of replication and segregation. Until recently, the mechanisms by which animal and plant cells maintain a constant surface area have been considered to be distinct. The prevailing view was that surface area was maintained in dividing animal cells through temporally separated rounds of membrane expansion and membrane invagination. The latter event, known as cytokinesis, produces two physically distinct daughter cells and has been thought to be primarily driven by actomyosin-based constriction. By contrast, membrane addition seems to be the primary mechanism that drives cytokinesis in plants and, thus, the two events are linked mechanistically and temporally. In this article (which is part of the Cytokinesis series), we discuss recent studies of a variety of organisms that have made a convincing case for membrane trafficking at the cleavage furrow being a key component of both animal and plant cytokinesis.     

Characterization of a cytokinesis defective (cyd1) mutant of Arabidopsis.

Although several mutations and genes affecting plant cytokinesis have been identified, mutant screens are not yet saturated and knowledge about gene function is still limited. A novel Arabidopsis mutation, cytokinesis defective1 (cyd1), was identified by partial or missing cell walls in stomata. Stomata with incomplete or no cytokinesis still differentiate and some contain swellings of the outer wall not found in the wild type. The incomplete walls are correctly placed opposite stomatal wall thickenings suggesting that the mutation interferes with the execution of cytokinesis rather than with the placement of the division site. Cytokinesis defects are also detectable in other cell types throughout the plant, defects which include cell wall protrusions, two or more nuclei in one cell, and reduced cell number. The extent of cytokinetic partitioning correlates with nuclear number in abnormal stomata. Many cyd1 epidermal cells, stomata and pollen are larger, and trichomes have more branches. cyd1 is partially lethal with poor seed set and some defective ovules, but many plants are fertile despite abnormalities in vegetative and reproductive development such as missing, reduced, fused or misshapen leaves and floral organs. cyd1 appears to be the only cytokinesis mutant described where defects are known to occur in both mature vegetative and reproductive organs. Thus, the CYD1 gene product appears to be necessary for the execution of cytokinesis throughout the shoot. The examination of stomata by microscopy may be a useful screen for the directed isolation of additional cytokinesis mutations that are not embryo or seedling lethal     

Spatial aspects of cytokinesis in plant cells

Plant cytokinesis in a particular orientation and location can be viewed as having several component stages, often beginning with the establishment of division polarity before karyokinesis occurs. Improved methods for preserving the in situ distribution of actin microfilaments and observations of individual live cells during treatment with cytoskeleton-disrupting drugs are making it possible to elucidate the roles of microtubules and microfilaments in cytokinesis. Current evidence points to involvement of the cytoskeleton throughout the stages of preparation for, and execution of, cytokinesis in many types of plant cell division.     

A unifying new model of cytokinesis for the dividing plant and animal cells

Cytokinesis ensures proper partitioning of the nucleocytoplasmic contents into two daughter cells. It has generally been thought that cytokinesis is accomplished differently in animals and plants because of the differences in the preparatory phases, into the centrosomal or acentrosomal nature of the process, the presence or absence of rigid cell walls, and on the basis of 'outside-in' or 'inside-out' mechanism. However, this long-standing paradigm needs further reevaluation based on new findings. Recent advances reveal that plant cells, similarly to animal cells, possess astral microtubules that regulate the cell division plane. Furthermore, endocytosis has been found to be important for cytokinesis in animal and plant cells: vesicles containing endocytosed cargo provide material for the cell plate formation in plants and for closure of the midbody channel in animals. Thus, although the preparatory phases of the cell division process differ between plant and animal cells, the later phases show similarities. We unify these findings in a model that suggests a conserved mode of cytokinesis.     

Dynamics of microtubular cytoskeleton during meiosis in higher plants. VIII. Comparison between successive and simultaneous cytokinesis

The abnormal cytoskeleton cycle in meiosis in pollen mother cells of cereal wide hybrids F reveals the role of polar microtubules in phragmoplast formation during successive cytokinesis. The cytoskeletal rearrangements during successive and simultaneous cytokinesis in higher plant meiosis are compared.