Control of Actin Ring Formation During Cell Division in Aspergillus

在准备细胞分裂时，动物和真菌细胞都聚集在皮质肌动蛋白环上。这个环的形成似乎在时间和空间上受到有丝分裂核信号的控制。目前的模型表明，肌动蛋白环通过两种可能的机制影响细胞分裂。在动物和某些真菌中，肌动蛋白环收缩，将细胞一分为二。在其他真菌中，环定义了一个区域，在这里形成细胞板来分裂细胞。无论使用何种机制，肌动蛋白环对细胞分裂至关重要。以前的研究采用各种生化和遗传方法已经确定了许多形成和/或肌动蛋白环功能所必需的蛋白质。然而，目前还不清楚这些蛋白质如何以一种综合的方式控制细胞分裂。此外，越来越明显的是，肌动蛋白环蛋白的完整清单尚未获得。Harris博士的研究项目的总体目标是利用遗传学的力量来识别和表征肌动蛋白环形成和功能所需的其他蛋白质，从而阐明遗传易感丝状真菌——细粒曲霉（Aspergillus nidulans）细胞分裂的分子机制。这种真菌通过形成被称为隔的横壁进行细胞质分裂。针叶草中隔的形成在时间和空间上与有丝分裂协调，需要形成一个收缩的肌动蛋白环。基因筛选导致鉴定和表征基因产物，在不同步骤的作用，以控制割裂草。例如，sepB突变体的分析揭示了一个检查点的存在，它可以在DNA损伤的情况下防止隔膜的形成。相反，sepA突变体的特征导致鉴定出一种进化上保守的蛋白，该蛋白可能控制肌动蛋白环的组装。本研究项目的目的是解决sepA基因产物通过促进收缩肌动蛋白环的形成在隔膜形成中起重要作用的假设。具体来说，Harris博士将使用间接免疫荧光来确定SepA是否定位于早期分裂部位。此外，他将建立SepA定位的时间相对于有丝分裂和肌动蛋白环的形成。他还计划采用一系列遗传和生化方法来识别与SepA相互作用的蛋白质。特别是，他将测试SepA功能需要与肌动蛋白相关蛋白谱和septin相互作用的预测。细胞质分裂是一个令人着迷的过程，在这个过程中，一个活细胞将自己分离成两个后代细胞，这是生命本质的基础。该研究项目将有助于更好地理解细胞分裂的一般机制。使用丝状真菌作为本研究的模式生物是一个特别好的选择，因为真菌具有显著的社会影响。一方面，一些真菌引起疾病；另一方面，它们可以产生有用的天然产物，如抗生素和商业上重要的酶，并且可以通过基因工程生产具有商业价值的非真菌蛋白质。因此，对隔膜形成如何允许丝状真菌生长和繁殖的理解的增加可以导致对抗植物，动物和人类真菌感染的方法，以及允许真菌更有效地用作工业生物催化剂，用于生产商业上重要的酶和其他蛋白质。＊＊＊

9723711 Harris In preparation for cytokinesis, both animal and fungal cells assemble a cortical actin ring. The formation of this ring appears to be temporally and spatially controlled by signals from mitotic nuclei. Current models suggest that the actin ring functions via two possible mechanisms to effect cytokinesis. In animals and certain fungi, the actin ring contracts, splitting cells in two. In other fungi, the ring defines a region where a cell plate forms to divide the cell. Regardless of mechanism used, the actin ring is essential for cytokinesis. Previous studies employing various biochemical and genetic approaches have identified numerous proteins necessary for the formation and/or function of the actin ring. However, it is not at all clear how these proteins function in an integrated manner to control cytokinesis. Moreover, it has become increasingly evident that a complete inventory of actin ring proteins has not been attained. The overall objective of Dr. Harris' research program is to use the power of genetics to identify and characterize additional proteins required for the formation and function of the actin ring, and thereby elucidate the molecular mechanisms underlying cytokinesis in the genetically tractable filamentous fungus, Aspergillus nidulans. This fungus undergoes cytokinesis by forming crosswalls known as septa. Septum formation in A. nidulans is temporally and spatially coordinated with mitosis, and requires the formation of a contractile actin ring. Genetic screens have resulted in the identification and characterization of gene products which act at different steps to control septation in A. nidulans. For example, the analysis of sepB mutants has revealed the existence of a checkpoint which prevents septum formation in the presence of DNA damage. In contrast, the characterization of sepA mutants has led to the identification of an evolutionarily conserved protein that may control the assembly of the actin ring. The objective of this research project is to address the hypothesis that the sepA gene product plays an essential role in septum formation by promoting the formation of the contractile actin ring. Specifically, Dr. Harris will use indirect immunofluorescence to determine if SepA localizes to the incipient division site. In addition, he will establish the timing of SepA localization relative to mitosis and actin ring formation. He also plans to employ a battery of genetic and biochemical approaches to identify proteins that interact with SepA. In particular, he will test predictions that SepA function requires interactions with the actin-associated protein profilin and with the septins. The fascinating process of cytokinesis, in which a living cell literally separates itself into two progeny cells, underpins the nature of life. This research project should lead to a better understanding of the general mechanisms underlying cytokinesis. The use of a filamentous fungus as the model organism in this study is a particularly good choice because of the pronounced societal impact of fungi. On the one hand, some fungi cause diseases; on the other hand, they produce useful natural products such as antibiotics and commercially important enzymes, and can be genetically engineered to produce non-fungal proteins of commercial interest. Thus, an increased understanding of how septum formation permits filamentous fungi to grow and reproduce can lead to ways of combating fungal infections of plants, animals, and humans, as well as allowing fungi to be used more efficiently as industrial biocatalysts for the production of commercially important enzymes and other proteins. ***