Molecular relativity: tracking single molecule movement relative to cell structures

荧光显微镜对细胞生物学家来说是一个至关重要的工具，因为它允许他们用荧光分子（荧光团）标记不同的蛋白质，并在活细胞中观察它们。由此产生的信息可以帮助我们了解疾病，并找到治疗疾病的新药。为了了解细胞中分子的行为，可以对带有荧光团标记的单个分子进行成像并测量其速度。然而，目前这只能在细胞膜上进行，或者在细胞保持静止的部分进行。如果分子附着的细胞部分移动了，就不可能弄清楚哪些是由于分子的移动，哪些是由于分子附着的结构的移动。我们建议解决这个问题，以便在运动结构中进行跟踪研究。为了做到这一点，我们将利用可光切换荧光团的特性。这些荧光团可以在发出两种不同颜色的光之间切换。通常只记录一种颜色，其中只有少数荧光团发光。这意味着单个分子可以被追踪。我们想开发一个系统来同时成像两种发射状态。这将使我们在一个通道中对样品的结构进行成像，在另一个通道中对单个分子进行成像。这可以通过同时用两个激光器照射样品并将发射的光在相机芯片的两个部分上分开来完成，分裂是基于颜色的。为了从这个系统中获得有用的信息，我们需要开发一种新的数据分析方法。单分子的位置和样品的结构都需要进行拟合和跟踪。然后，样品结构的运动可以用来校正单个分子的轨迹。我们将尝试两种不同的方法来对结构进行建模，首先是一种简单的方法，将其近似为一系列直线，然后是一种更精确的模型，将其拟合为曲线。样本结构的图像包含我们将尝试提取的附加信息。这是因为这些图像中的分子，虽然密集排列，但随着时间的推移而移动，并在发光或不发光的状态之间切换。这些信息可以以两种方式使用。首先，通过分析短序列图像和利用荧光团波动信息来提高对荧光团位置的了解，从而提高样品结构的分辨率。第二，获取分子在细胞结构中平均如何运动的信息。这是通过比较不同帧之间图像补丁的亮度来完成的。这两种方法将使我们能够更准确地看到细胞结构，并将单个分子的运动方式与结构中分子的平均运动方式进行比较。这种方法将允许细胞生物学家在快速移动的结构中追踪单个分子。单分子跟踪已经为那些可以使用它的结构产生了重要的结果，我们的工作将使这项技术适用于更广泛的细胞生物学问题。

Fluorescence microscopy is a crucial tool for cell biologists because it allows them to label different proteins with fluorescent molecules (fluorophores) and observe them in live cells. This yields information which can help us to understand diseases, and find new drugs to treat them. To understand how molecules in a cell behave, individual molecules labelled with fluorophores can be imaged and their speed measured. However, currently this can only be done on the membrane of cells, or on parts of the cell that stay very still. If the part of the cell which the molecule is attached to moves, it isn't possible to work out what is due to the movement of the molecule and what is due to the movement of the structure the molecule is attached to.We propose to solve this problem, so that tracking studies can be carried out in moving structures. To do this we will use the properties of photoswitchable fluorophores. These are fluorophores which can be switched between emitting light in two different colours. Normally only one colour is recorded, in which only a few fluorophores emit light. This means that individual molecules can be tracked. We want to develop a system to simultaneously image both of the emitting states. This will let us image the structure of the sample in one channel, and individual molecules in another. This can be done by illuminating the sample with two lasers simultaneously and splitting the emitted light across two sections of a camera chip, with the split being based on colour.To get useful information from this system, we will need to develop a new data analysis method. Both the positions of the single molecules and the structure of the sample will need to be fitted and tracked. The movement of the structure of the sample can then be used to correct the tracks of individual molecules. We will try two different methods to model the structure, first a simple method where it is approximated as a series of straight lines, and then a more accurate model where it is fitted as a curve.The images of the structure of the sample contain additional information which we will also try to extract. This is because the molecules in these images, while densely packed, are moving over time and switching between states in which they emit or don't emit light. This information can be used in two ways. First, to get enhanced resolution of the structure of the sample by analysing a short sequence of images and using information from fluorophore fluctuations to improve knowledge of the fluorophore positions. Second, to get information about how the molecules are moving around the cell structure on average. This is done by comparing the brightness of image patches between different frames. These two methods will allow us to visualise the cell structure more accurately, and to compare how individual molecules move to how the molecules in the structure are moving on average.This method would allow cell biologists to track single molecules in rapidly moving structures. Single molecule tracking has produced important results for those structures with which it can be used, and our work would make this technique applicable to a much wider range of cell biology problems.