Establishment of the Growth Axis and Alignment of the Division Plane in Pelvetia Zygotes

Pelvetia 合子生长轴的建立和分界面的对准

• 批准号: 9807811
• 负责人: Darryl Kropf
• 金额: $ 34.5万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-07-15 至 2002-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9807811&HistoricalAwards=false
• 关键词: Establishment; Growth; Axis; Alignment; Division

Establishment of embryonic axes is fundamental to the development of eukaryotic organisms, yet very little is known about this process in plants because the embryo is retained inside maternal tissues and is difficult to isolate. In contrast, zygotes of the brown algae, Fucus sp. and Pelvetia sp., are easily harvested from seawater and have long served as model organisms for investigation of polarity establishment. For the past nine years the Kropf lab has been studying the cell biology and physiology of polarization in P. compressa zygotes focusing primarily on the roles of cytosolic ions and the cytoskeleton. Based upon this research, and that from other laboratories, the Kropf lab has formulated a working model to account for establishment of the growth axis and the precise orientation of the division plane. Briefly, this model postulates that the rhizoid pole of the growth (rhizoid-thallus) axis is marked by a patch of cortical F-actin and that the division plane is determined by the orientation of centrosomes on the nuclear envelope. Sperm entry is postulated to induce both axes by causing assembly of an F-actin patch at the sperm entry site and by introducing centrioles into the egg cytoplasm. Over the first few hours of development, the F-actin patch, and hence the growth axis, can be repositioned in response to environmental cues. The centrosomal axis does not respond to environmental cues and therefore the two axes develop independently of one another. The PI speculates that the F-actin patch at the rhizoid pole defines a target site for secretion, and that polar secretion of molecules locally into the rhizoid plasma membrane and cell wall amplifies the nascent growth axis. After growth begins at the rhizoid pole, and just prior to first mitosis, the centrosomal axis rotates into parallel alignment with the growth axis. The spindle poles form from the aligned centrosomes and cytokinesis bisects the spindle, ensuring that the division plane is transverse to the growth axis.The proposed research will test the salient aspects of this working model. The primary objectives are to:1) determine whether sperm entry induces an initial polarity2) demonstrate that a patch of F-actin marks the rhizoid pole of the axis3) investigate the mechanism of polar secretion4) analyze the role of microtubules (MTs) in rotational alignment of the centrosomes5) clarify the role of plasma membrane-cell wall adhesions in rotational alignment6) investigate regulation of the cytoskeletal arrays by cytosolic H+ activityConfirmation of our working model will provide the first comprehensive picture of the role of the cytoskeleton in polarity establishment and expression in fucoid zygotes, and will initiate important studies on polar secretion and cytoskeletal regulation by H+. This study will also provide a paradigm for future investigations of polarity establishment in higher plant embryos.

胚轴的建立是真核生物发育的基础，但对植物中的这一过程知之甚少，因为胚胎保留在母体组织中，难以分离。相反，褐藻墨角藻和Pelvetia sp.的受精卵，很容易从海水中收获，长期以来一直是研究极性建立的模式生物。在过去的九年里，Kropf实验室一直在研究扁实贝受精卵的细胞生物学和极化生理学，主要集中在细胞溶质离子和细胞骨架的作用上。基于这项研究，以及其他实验室的研究，Kropf实验室制定了一个工作模型，以解释生长轴的建立和分割平面的精确方向。简而言之，这个模型假设，假根极的生长（假根-叶状体）轴是由一个补丁的皮质F-肌动蛋白和分裂平面是由核膜上的中心体的方向确定的。精子进入被假定为通过在精子进入位点引起F-肌动蛋白补丁的组装和通过将中心粒引入卵细胞质来诱导两个轴。在发育的最初几个小时里，F-肌动蛋白补丁，因此生长轴，可以重新定位以响应环境线索。中心体轴不响应环境线索，因此两个轴彼此独立地发展。PI推测，在假根极的F-肌动蛋白补丁定义了一个目标网站的分泌，和极性分泌的分子局部进入假根质膜和细胞壁放大新生的生长轴。在假根极开始生长后，在第一次有丝分裂之前，中心体轴旋转成与生长轴平行排列。纺锤体的两极是由排列整齐的中心体形成的，胞质分裂将纺锤体一分为二，确保分裂平面与生长轴垂直。主要目的是：1）确定精子进入是否诱导初始极性2）证明一片F-肌动蛋白标记轴突的假根极3）研究极性分泌的机制4）分析微管（MT）在中心体旋转排列中的作用5）澄清质膜-细胞壁粘附在旋转排列中的作用6）研究细胞溶质H+活性对细胞骨架阵列的调节我们的工作模型的确认将首次全面了解细胞骨架在岩藻合子极性建立和表达中的作用，并将启动关于极性分泌和H+对细胞骨架调节的重要研究。本研究也将为今后高等植物胚极性建立的研究提供一个范例。