Heterotrimeric G Protein Regulation of Chemotropism in Yeast

趋化性，或对化学吸引剂或驱避剂的化学梯度作出反应的定向细胞运动，在发育和免疫中起着至关重要的作用。趋化性的相关现象(对化学梯度的定向细胞生长)是神经系统发育、血管发育、植物授粉和真菌感染所不可或缺的。自然形成的化学梯度非常浅，而且是动态的。单元格如何使用如此微妙的提示进行导航？趋化现象的模型调用正反馈环路，将细胞表面受体激活的微小差异放大为实质上更陡峭的细胞内信号梯度。据推测，趋化细胞对浅层化学梯度的反应也通过相互作用的反馈环被放大，但对这种环的机制缺乏了解。萌芽酵母的交配反应是趋化性的：交配细胞解释复杂的信息素梯度，并将它们的生长极化在最接近的伴侣的方向上。梯度感应既依赖于一种名为信息素受体的表面蛋白质，也依赖于一种名为GGamma的相关蛋白质。一旦信息素刺激受体，GGamma就会启动大量蛋白质的组装，形成趋化复合体，在适当的位置催化细胞的生长。目前尚不清楚细胞如何感知方向并正确定位生长部位，本项目的目标是了解酵母细胞如何启动朝向交配伙伴的定向生长。这项研究将从机制上理解GGamma磷酸化在酵母趋化反应中所起的作用。由于对其他真核生物的趋化反应中的定向感知知之甚少，这项工作可能会产生广泛影响趋化现象研究的一般原理。布罗德影响PI带头开发了NSF/Capstone为芝加哥伊利诺伊大学生物科学专业优等生开设的本科生研究项目，目前正在管理该项目。学生们与导师配对进行一学期的阅读，然后进行四个学期的研究，最终在NSF/Capstone年度小型研讨会上正式展示他们的工作。至少有两名NSF/Capstone的学生将在该项目的学年和暑期期间在PI的实验室工作。该项目博士后研究员的培训计划包括学习本次调查所需的分子遗传学和成像方法，在生物化学方法方面指导本科生和研究生，在研究生水平的信号转导课程中讲课，提交年度系级研讨会，以及开发和资助他们自己的独立研究计划。学员将有机会通过与罗伯特·阿科维茨博士(法国尼斯大学)的合作，在国外进行研究，阿科维茨博士是该项目的合作者之一。

Chemotaxis, or directed cell movement in response to a chemical gradient of a chemoattractant or repellent, plays a vital role in development and immunity. The related phenomenon of chemotropism (directed cell growth in response to a chemical gradient) is integral to the development of the nervous system, blood vessel development, plant pollination and fungal infection. Naturally occurring chemical gradients are very shallow and dynamic. How do cells navigate using such subtle cues? Models of chemotactic phenomena invoke positive feedback loops that amplify small differences in receptor activation across the cell surface into a substantially steeper intracellular signaling gradient. It is presumed that the response of chemotropic cells to shallow chemical gradients is also amplified by interacting feedback loops, but a mechanistic understanding of such loops is lacking. The mating response of the budding yeast Saccharomyces cerevisiae is chemotropic: mating cells interpret complex pheromone gradients and polarize their growth in the direction of the closest partner. Gradient sensing depends on both a surface protein called the pheromone receptor, and an associated protein called Ggamma. Upon pheromone stimulation of the receptor, Ggamma initiates the assembly of numerous proteins into what is known as the chemotropic complex, which catalyzes growth of the cell at the appropriate site. It is not known how the cell senses direction and correctly orients the growth site, and the goal of this project is to understand how yeast cells initiate directional growth toward a mating partner. This investigation will provide a mechanistic understanding of the role that Ggamma phosphorylation plays in the yeast chemotropic response. Because little is known about directional sensing during the chemotropic responses of other eukaryotes, general principles are likely to emerge from this work that will broadly influence the study of chemotropic phenomena.Broader ImpactsThe PI spearheaded the development of and is now administering the NSF/Capstone Undergraduate Research Program for honors students majoring in Biological Sciences at the University of Illinois at Chicago. Students are paired with a mentor for a semester of reading followed by four semesters of research leading to a formal presentation of their work at the annual NSF/Capstone mini-symposium. A minimum of two NSF/Capstone students will work in the PI's lab during the academic year and summertime during this project. The training plan for the postdoctoral fellow on the project includes learning the molecular genetic and imaging methods required in this investigation, mentoring undergraduate and graduate students in biochemical approaches, lecturing in a graduate level signal transduction course, presenting an annual departmental seminar, and developing and funding their own independent research program. Trainees will have an opportunity to undertake research abroad, through collaboration with Dr. Robert Arkowitz (University of Nice, France), a collaborator in this project.