Shaw S L, Quatrano R S
Department of Biology, University of North Carolina, Chapel Hill 27599-3280, USA.
Development. 1996 Sep;122(9):2623-30. doi: 10.1242/dev.122.9.2623.
In this study, we investigate the role of polar secretion and the resulting asymmetry in the cell wall in establishing polarity in Fucus zygotes. We have utilized brefeldin-A to selectively interrupt secretion of Golgi-derived material into the cell wall as assayed by toluidine blue O staining of sulfated fucoidin. We show that the polar secretion of Golgi-derived material is targeted to a cortical site of the zygote identified by the localization of actin filaments and dihydropyridine receptors. The deposition of Golgi-derived material into the cell wall at this target site is temporally coincident with and required for polar axis fixation. We propose that local secretion of Golgi-derived material into the cell wall transforms the target site into the fixed site of polar growth. We also found that polar secretion of Golgi-derived material at the fixed site is essential for growth and differentiation of the rhizoid, as well as for the proper positioning of the first plane of cell division. We propose that the resulting asymmetry in the cell wall serves as positional information for the underlying cortex to initiate these polar events. Our data supports the hypothesis that cell wall factors in embryos, previously shown to be responsible for induction of rhizoid cell differentiation, are deposited simultaneously with and are responsible for polar axis fixation. Furthermore, the pattern of polar growth is attributable to a positional signal at the fixed site and appears to be independent of the orientation of the first cell division plane. Thus, the establishment of zygotic cell polarity and not the position of the first division plane, is critical for the formation of the initial embryonic pattern in Fucus.
在本研究中，我们探究了极性分泌以及细胞壁中由此产生的不对称性在墨角藻合子建立极性过程中的作用。我们利用布雷菲德菌素A来选择性地阻断高尔基体衍生物质向细胞壁的分泌，这通过对硫酸化岩藻多糖进行甲苯胺蓝O染色来检测。我们发现，高尔基体衍生物质的极性分泌靶向到合子的一个皮质位点，该位点可通过肌动蛋白丝和二氢吡啶受体的定位来确定。高尔基体衍生物质在这个靶位点沉积到细胞壁的过程与极轴固定在时间上同步且是极轴固定所必需的。我们提出，高尔基体衍生物质向细胞壁的局部分泌将靶位点转变为极性生长的固定位点。我们还发现，在固定位点高尔基体衍生物质的极性分泌对于假根的生长和分化以及细胞分裂第一平面的正确定位至关重要。我们提出，细胞壁中由此产生的不对称性作为一种位置信息，供其下方的皮质启动这些极性事件。我们的数据支持这样一种假说，即胚胎中的细胞壁因子，先前已证明其负责诱导假根细胞分化，与极轴固定同时沉积且负责极轴固定。此外，极性生长模式归因于固定位点的一个位置信号，并且似乎与细胞分裂第一平面的方向无关。因此，合子细胞极性的建立而非第一分裂平面的位置，对于墨角藻初始胚胎模式的形成至关重要。
