Tracking shallow and dynamic chemoattractant gradients - how yeast cells amplify both internal and external signals to locate mating partners

这个项目将有助于我们理解梯度感应，细胞感知其表面化学浓度的微小差异，从而定位刺激源的能力。这种现象对所有生物体的发育和健康至关重要。PI使用酵母细胞作为模型来研究梯度传感的分子机制，这被认为广泛适用于更复杂的生物体中的细胞。在之前的研究中，他发现了一种“梯度跟踪机器”，细胞必须在能够感知化学源的方向之前进行组装。在这项研究中，他将继续研究这台机器如何解码化学梯度。在此项目期间，PI和他的高级研究专家将指导来自芝加哥城市学院的生物学学生，以提高他们从四年制大学毕业并获得STEM领域学士学位的机会。拟议的本科研究和指导计划旨在激励，指导，建议和支持对STEM职业感兴趣的代表性不足的学生。每年将根据他们的学术潜力和在四年制院校攻读STEM专业的动机，选择两名优秀的候选人参加。通过参加定期辅导课程，PI实验室的带薪暑期研究实习和公共宣传活动，学生将获得进行科学研究的经验，批判性地评估他人研究的能力，并练习展示他们的工作。该计划预计将增加八名学生在四年制院校成为理科专业学生的机会。该研究还将通过与不同领域的专家合作，为PI的学生提供跨学科的培训。最著名的梯度刺激细胞输出，趋化性（定向细胞运动）和趋化性（定向细胞生长）是广泛的生物过程所必需的。虽然它们最终表现出完全不同的行为，趋化性和趋化性细胞面临着类似的挑战：响应细胞必须感觉到其表面化学浓度的微小差异，确定梯度源的方向，并使其细胞骨架朝向它。酿酒酵母是趋化性的：交配细胞解释复杂的信息素梯度，并使它们的生长朝着最接近的伴侣的方向。像许多化学传感细胞一样，酵母使用G蛋白偶联受体来检测化学引诱物。该项目的目标是了解酵母细胞如何在浅层，复杂和动态信息素梯度中准确感知方向。基于在以前的项目中所做的发现，PI发表了一个梯度传感的确定性模型，该模型从广义上解释了酵母细胞如何将其表面上激活受体的微小差异转化为准确和强大的方向响应。交配酵母最初忽略信息素梯度，因为它们首先将信号、极性和运输蛋白质共定位到它们用于出芽的默认极性位点，从而构建“梯度跟踪机”（GTM）。一旦组装好，GTM就沿着质膜移动到最大信息素浓度的点，在那里它标记了用于交配的趋化位点。G蛋白信号传导的主要负调节因子RGS蛋白Sst 2对于该过程是必不可少的，并且G蛋白亚基之一（G β γ）的磷酸化起着关键作用。这项研究的重点是了解Sst 2是如何在空间和时间上控制的，G蛋白亚基的磷酸化如何有助于梯度跟踪，以及GTM之间的动态相互通信如何使交配伙伴能够朝向共同的融合位点。这个奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project will contribute to our understanding of gradient sensing, the ability of cells to sense small differences in chemical concentration across their surfaces, and thereby locate the source of the stimulus. This phenomenon is essential for the development and health of all organisms. The PI uses yeast cells as a model to study the molecular mechanisms underlying gradient sensing, which are thought to be broadly applicable to cells in more complex organisms. In previous studies, he discovered a “gradient tracking machine” that cells must assemble before they are able to sense the direction of the chemical source. In this investigation, he will continue to investigate how this machine functions to decode chemical gradients. During this project period, the PI and his senior research specialist will mentor select biology students from the City Colleges of Chicago, to enhance their chances of graduating from a four-year institution with a BS in a STEM field. The proposed undergraduate research and mentoring program is designed to inspire, instruct, advise, and support underrepresented students who are interested in a STEM career. Two outstanding candidates will be chosen to participate each year based on their academic potential and motivation to pursue a STEM major at a four-year institution. By participating in regular tutoring sessions, paid summer research internships in the PI’s lab, and public outreach events, students will gain experience conducting scientific research, an ability to critically evaluate the research of others, and practice presenting their work. This program is expected to increase the chances of eight students to succeed as science majors at four-year institutions. The investigation will also provide the PI's students with interdisciplinary training through interactions with collaborators who are experts in diverse areas.The best-known gradient-stimulated cellular outputs, chemotaxis (directed cell movement), and chemotropism (directed cell growth), are required for a wide range of biological processes. Although they ultimately exhibit quite different behavior, chemotactic and chemotropic cells face similar challenges: the responding cell must sense small differences in chemical concentration across its surface, determine the direction of the gradient source, and polarize its cytoskeleton toward it. The mating response of the budding yeast S. cerevisiae is chemotropic: mating cells interpret complex pheromone gradients and polarize their growth in the direction of the closest partner. Like many chemosensing cells, yeasts use G protein-coupled receptors to detect chemoattractant. The goal of this project is to understand how yeast cells accurately sense direction in shallow, complex, and dynamic pheromone gradients. Based on discoveries made in a previous project, the PI published a deterministic model of gradient sensing that explains, in broad terms, how yeast cells translate a vanishingly small differential of activated receptors across their surfaces into accurate and robust directional responses. Mating yeast initially ignore the pheromone gradient, as they first colocalize signaling, polarity, and trafficking proteins to the default polarity site they use for budding, building a “gradient tracking machine” (GTM). Once assembled, the GTM moves along the plasma membrane to the point of maximal pheromone concentration, where it marks the chemotropic site used for mating. The primary negative regulator of G-protein signaling, the RGS protein Sst2, is essential for this process, and phosphorylation of one of the G-protein subunits (Gbetagamma)plays a critical role. The priorities of this investigation are to learn how Sst2 is controlled in space and time, how the phosphorylation of the G protein subunit contributes to gradient tracking, and how dynamic intercommunication between GTMs enables mating partners to orient toward a common fusion site. These questions will be answered using imaging, genetic, biochemical, proteomic, and computational approaches.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.