Katsaros Christos, Karyophyllis Demosthenes, Galatis Basil
University of Athens, Faculty of Biology, Department of Botany, Athens 157 84, Greece.
Ann Bot. 2006 May;97(5):679-93. doi: 10.1093/aob/mcl023. Epub 2006 Feb 8.
Morphogenesis on a cellular level includes processes in which cytoskeleton and cell wall expansion are strongly involved. In brown algal zygotes, microtubules (MTs) and actin filaments (AFs) participate in polarity axis fixation, cell division and tip growth. Brown algal vegetative cells lack a cortical MT cytoskeleton, and are characterized by centriole-bearing centrosomes, which function as microtubule organizing centres.
Extensive electron microscope and immunofluorescence studies of MT organization in different types of brown algal cells have shown that MTs constitute a major cytoskeletal component, indispensable for cell morphogenesis. Apart from participating in mitosis and cytokinesis, they are also involved in the expression and maintenance of polarity of particular cell types. Disruption of MTs after Nocodazole treatment inhibits cell growth, causing bulging and/or bending of apical cells, thickening of the tip cell wall, and affecting the nuclear positioning. Staining of F-actin using Rhodamine-Phalloidin, revealed a rich network consisting of perinuclear, endoplasmic and cortical AFs. AFs participate in mitosis by the organization of an F-actin spindle and in cytokinesis by an F-actin disc. They are also involved in the maintenance of polarity of apical cells, as well as in lateral branch initiation. The cortical system of AFs was found related to the orientation of cellulose microfibrils (MFs), and therefore to cell wall morphogenesis. This is expressed by the coincidence in the orientation between cortical AFs and the depositing MFs. Treatment with cytochalasin B inhibits mitosis and cytokinesis, as well as tip growth of apical cells, and causes abnormal deposition of MFs.
Both the cytoskeletal elements studied so far, i.e. MTs and AFs are implicated in brown algal cell morphogenesis, expressed in their relationship with cell wall morphogenesis, polarization, spindle organization and cytokinetic mechanism. The novelty is the role of AFs and their possible co-operation with MTs.
细胞水平上的形态发生包括细胞骨架和细胞壁扩展密切参与的过程。在褐藻合子中，微管（MTs）和肌动蛋白丝（AFs）参与极性轴固定、细胞分裂和顶端生长。褐藻营养细胞缺乏皮质MT细胞骨架，其特征是带有中心粒的中心体，作为微管组织中心发挥作用。
对不同类型褐藻细胞中MT组织进行的广泛电子显微镜和免疫荧光研究表明，MTs构成细胞形态发生不可或缺的主要细胞骨架成分。除了参与有丝分裂和胞质分裂外，它们还参与特定细胞类型极性的表达和维持。诺考达唑处理后MTs的破坏会抑制细胞生长，导致顶端细胞鼓起和/或弯曲、顶端细胞壁增厚，并影响核定位。用罗丹明 - 鬼笔环肽对F - 肌动蛋白进行染色，揭示了一个由核周、内质和皮质AFs组成的丰富网络。AFs通过组织F - 肌动蛋白纺锤体参与有丝分裂，并通过F - 肌动蛋白盘参与胞质分裂。它们还参与顶端细胞极性的维持以及侧枝起始。发现AFs的皮质系统与纤维素微纤丝（MFs）的取向有关，因此与细胞壁形态发生有关。这表现为皮质AFs与沉积的MFs之间取向的一致性。用细胞松弛素B处理会抑制有丝分裂和胞质分裂以及顶端细胞的顶端生长，并导致MFs的异常沉积。
到目前为止研究的两种细胞骨架成分，即MTs和AFs都与褐藻细胞形态发生有关，表现为它们与细胞壁形态发生、极化、纺锤体组织和胞质分裂机制的关系。新颖之处在于AFs的作用及其与MTs可能的合作。
