Investigating the mechanisms of phosphatidylcholine sensing

生物膜对生命的各个方面都是必不可少的；它们将细胞内部与环境分开；它们将细胞内的空间组织成几个隔间或细胞器，每个隔间或细胞器都有自己的特定作用；它们还可以作为发生复杂化学反应的平台。膜的基本构件是脂类。因此，细胞在正确的时间和地点产生脂质是至关重要的。必须仔细控制膜脂的数量和类型，以满足每个细胞的特定要求：例如，快速增殖的细胞或扩大其细胞内细胞器的细胞需要更多的脂类合成来支持相应膜的生长。在这个项目中，我们将研究细胞如何监测和调节磷脂酰胆碱(PC)的水平，卵磷脂是真核生物膜中含量最丰富的脂肪。由于PC是一种圆柱形脂质，它的耗尽会破坏膜内适当的脂质堆积；CCTA可以感觉到这一点，然后激活CCTA来纠正缺陷。我们最近发现，这一过程发生在许多不同的真核细胞的细胞核内：当CCTA不活跃时，CCTA是在核内，而当细胞需要制造更多的PC时，该酶与核膜内侧相联系，核膜内侧将细胞核与细胞质分开。考虑到脂质合成主要是细胞质过程，这一发现令人惊讶。在拟议的工作中，我们将确定CCTA是如何与核内膜结合的，为什么这个过程被限制在细胞核内，以及它如何与发生在细胞质中的PC合成的最后一步相协调。我们最近的工作表明，从简单的单细胞生物到人类，PC的感觉是高度保守的。因此，我们将对发芽酵母进行研究的初始发现阶段，作为一种提供快速洞察的模式生物；在第二阶段，我们将确定这些结果如何应用于人类细胞。我们相信，这项工作将有助于理解脂代谢的一个基本步骤，并可能指导未来的治疗方法，针对脂代谢和视觉障碍，这是由PC缺乏引起的。

Biological membranes are essential for all aspects of life; they separate the interior of cells from their environment; they organize the intracellular space into several compartments, or organelles, each with its own specific role; and they also function as platforms onto which complex chemical reactions take place. The basic building blocks of membranes are lipids. Therefore, it is critical that cells produce lipids at the right time and place. The amount and type of membrane lipids must be carefully controlled to match the specific requirements of each cell: for example, rapidly proliferating cells or cells expanding their intracellular organelles require more lipid synthesis to support the growth of the corresponding membranes. In this project we will investigate how cells monitor and adjust the levels of phosphatidylcholine (PC), the most abundant lipid in eukaryotic membranes.The enzyme that controls the rate of PC production is called CCTa. Because PC is a cylindrical lipid, its depletion disrupts proper lipid packing within the membrane; this is sensed by CCTa, which is then activated to correct the defect. We recently found that this process takes place inside the nucleus of many different eukaryotic cells: when inactive, CCTa is intranuclear, while when cells need to make more PC, the enzyme associates with the inner side of the nuclear membrane, which separates the nucleus from the cytoplasm. This finding is surprising given that lipid synthesis is mostly a cytoplasmic process. In the proposed work, we will determine how CCTa associates with the inner nuclear membrane, why this process is restricted within the nucleus and how it is coordinated with the final step of PC synthesis which takes place in the cytoplasm.Our recent work shows that the sensing of PC is highly conserved from simple unicellular organisms to humans. Therefore, we will carry out the initial discovery phase of our research in budding yeast as a model organism that provides rapid insights; in a second phase we will determine how these outcomes apply in human cells. We believe that this work will contribute to the understanding of a fundamental step in lipid metabolism and could guide future therapeutic approaches against lipid metabolic and visual disorders, which are caused by PC deficiency.