Developmental Polarity in Fucoid Zygotes

0110113岩藻褐藻的受精卵（受精卵）是研究在发育中的生物体中建立极性的机制的理想材料。 Kropf博士的实验室一段时间以来一直在研究细胞和生理机制，这些机制建立了一个生长轴，并确定了这些合子的分裂平面。 从这项工作中，他们制定了假设，以测试在这个奖项期间。 工作假设如下：生长轴规格。 Kropf博士提出，极性首先在受精时确定，精子进入的部位指定了生长轴的假根极。 该位点以细胞骨架元件F-肌动蛋白的局部组装为标志。 受精卵然后落在潮间带的岩石上，附着并开始监测其环境的空间信息，以帮助确定岩石底层的方向。 如果感知到相关矢量，则放弃精子诱导轴，并产生新的轴，使得新的假根极朝向岩石表面。 同时，肌动蛋白补丁在精子进入网站被拆卸和一个新的补丁组装在新生假根网站。 轴的重新对准可以在几个小时内重复发生。 最后，受精后12小时左右，在当前假根极生长扩展;形成的假根将合子牢固地附着在岩石上，并最终形成固定器。 Kropf博士推测，分裂平面是在有丝分裂末期确定的，因此新的细胞壁横向于由两个末期细胞核限定的轴沉积。 末期细胞核的方向由中心体位置决定。 中心体是父系遗传的，并分离到合子核的两侧。 最初，由两个中心体定义的轴与生长轴随机对齐，但在胞质分裂之前，中心体轴通过核旋转和纺锤体伸长的组合与生长轴对齐。 本提案中的研究将测试和扩展模型的最重要方面。 主要目的是1）研究动态肌动蛋白在指定生长轴中的需求，2）鉴定肌动蛋白成核分子，3）确定不对称细胞形状在分裂平面排列中的作用，4）评估末期纺锤体位置是否决定分裂平面，以及5）研究微管在定义分裂平面中的作用。

0110113KropfZygotes (fertilized eggs) of fucoid brown algae are ideal for investigating the mechanisms that establish polarity in developing organisms. Dr. Kropf's lab has for some time been investigating the cellular and physiological mechanisms that establish a growth axis and determine the division plane in these zygotes. From this work they have formulated hypotheses to be tested during this award period. The working hypotheses are as follows:Growth axis specification. Dr. Kropf proposes that polarity is first set in place at fertilization with the site of sperm entry specifying the rhizoid pole of the growth axis. This site is marked by local assembly of a cytoskeletal element, F-actin. The fertilized egg then settles onto the rocks in the intertidal zone, attaches and begins to monitor its environment for spatial information to help determine the direction of the rocky substratum. If relevant vectors are perceived, the sperm-induced axis is abandoned and a new axis is generated such the new rhizoid pole is toward the rock surface. Concomitantly, the actin patch at the sperm entry site is disassembled and a new patch is assembled at the nascent rhizoid site. Realignment of the axis can occur repeatedly over several hours. Finally, about 12 hours after fertilization, growth ensues at the current rhizoid pole; the rhizoid formed attaches the zygote firmly to rocks and eventually forms the holdfast of the alga.Division plane alignment. Dr. Kropf speculates that division plane is determined at telophase of mitosis such that the new cell wall is deposited transverse to the axis defined by the two telophase nuclei. The orientation of the telophase nuclei is determined by centrosomal position. Centrosomes are inherited paternally and separate to opposite sides of the zygotic nucleus. Initially, the axis defined by the two centrosomes is randomly aligned with the growth axis, but prior to cytokinesis the centrosomal axis becomes aligned with the growth axis by a combination of nuclear rotation and spindle elongation. Research in this proposal will test and extend the most important aspects of the models. The primary objectives are to 1) investigate the requirement for dynamic actin in specifying the growth axis, 2) identify actin nucleating molecules, 3) determine the role of asymmetric cell shape in division plane alignment, 4) assess whether telophase spindle position determines division plane, and 5) investigate the role of microtubules in defining the division plane.