Flanders D J, Rawlins D J, Shaw P J, Lloyd C W
Department of Cell Biology, John Innes Institute, Norwich, England.
J Cell Biol. 1990 Apr;110(4):1111-22. doi: 10.1083/jcb.110.4.1111.
To investigate the spatial relationship between the nucleus and the cortical division site, epidermal cells were selected in which the separation between these two areas is large. Avoiding enzyme treatment and air drying, Datura stramonium cells were labeled with antitubulin antibodies and the three-dimensional aspect of the cytoskeletons was reconstructed using computer-aided optical sectioning. In vacuolated cells preparing for division, the nucleus migrates into the center of the cell, suspended by transvacuolar strands. These strands are now shown to contain continuous bundles of microtubules which bridge the nucleus to the cortex. These nucleus-radiating microtubules adopt different configurations in cells of different shape. In elongated cells with more or less parallel side walls, oblique strands radiating from the nucleus to the long side walls are presumably unstable, for they are progressively realigned into a transverse disc (the phragmosome) as broad, cortical, preprophase bands (PPBs) become tighter. The phragmosome and the PPB are both known predictors of the division plane and our observations indicate that they align simultaneously in elongated epidermal cells. These observations suggest another hypothesis: that the PPB may contain microtubules polymerized from the nuclear surface. In elongated cells, the majority of the radiating microtubules, therefore, come to anchor the nucleus in the transverse plane, consistent with the observed tendency of such cells to divide perpendicular to the long axis. In nonrectangular isodiametric epidermal cells, which approximate regular hexagons in section, the radial microtubular strands emanating from the nucleus tend to remain associated with the middle of each subtending cell wall. The strands are not reorganized into a single dominant transverse bar, but remain as a starlike array until mitosis. PPBs in these cells are not as tight; they may only be a sparse accumulation of microtubules, even forming along non-diametrical radii. This arrangement is consistent with the irregular division patterns observed in epidermal mosaics of isodiametric D. stramonium cells. The various conformations of the radial strands can be modeled by springs held in two-dimensional hexagonal frames, and by soap bubbles in three-dimensional hexagonal frames, suggesting that the division plane may, by analogy, be selected by minimal path criteria. Such behavior offers a cytoplasmic explanation of long-standing empirically derived "rules" which state that the new cell wall tends to meet the maternal wall at right angles. The radial premitotic strands and their analogues avoid taking the longer path to the vertex of an angle where a cross wall is already present between neighboring cells.(ABSTRACT TRUNCATED AT 400 WORDS)
为了研究细胞核与皮层分裂位点之间的空间关系，我们选择了这两个区域间距较大的表皮细胞。在避免酶处理和空气干燥的情况下，用抗微管蛋白抗体标记曼陀罗细胞，并使用计算机辅助光学切片重建细胞骨架的三维结构。在准备分裂的液泡化细胞中，细胞核迁移到细胞中心，由跨液泡的丝状体悬挂着。现在发现这些丝状体包含连续的微管束，这些微管束将细胞核与皮层相连。这些从细胞核辐射出的微管在不同形状的细胞中呈现不同的构型。在具有或多或少平行侧壁的细长细胞中，从细胞核向长侧壁辐射的斜向丝状体可能是不稳定的，因为随着宽阔的皮层前期带（PPB）变得更紧密，它们会逐渐重新排列成一个横向盘状结构（成膜体）。成膜体和PPB都是已知的分裂平面预测因子，我们的观察表明它们在细长的表皮细胞中同时排列。这些观察结果提出了另一个假设：即PPB可能包含从核表面聚合的微管。因此，在细长细胞中，大多数辐射状微管将细胞核固定在横向平面上，这与观察到的此类细胞倾向于垂直于长轴分裂的趋势一致。在非矩形等径表皮细胞中，其截面近似正六边形，从细胞核发出的径向微管丝状体倾向于与每个对向细胞壁的中部保持关联。这些丝状体不会重新组织成单一的主导横向条带，而是保持星状排列直到有丝分裂。这些细胞中的PPB不那么紧密；它们可能只是微管的稀疏聚集，甚至沿着非直径半径形成。这种排列与在等径曼陀罗细胞的表皮镶嵌体中观察到的不规则分裂模式一致。径向丝状体的各种构象可以用二维六边形框架中的弹簧以及三维六边形框架中的肥皂泡来模拟，这表明分裂平面可能类似地通过最小路径标准来选择。这种行为为长期以来根据经验得出的“规则”提供了一种细胞质解释，该规则指出新细胞壁倾向于与母细胞壁成直角相交。有丝分裂前的径向丝状体及其类似物避免了沿着更长的路径到达相邻细胞之间已经存在横壁的角顶点。
