Adelboden冬季学校——链接物理与生物

On 26th to 29th of January, I attended a winter school together with other 4 group members in Adelboden in Switzerland. The winter school was organized by LCPPM (which stands for Laboratory of Physical Chemistry of Polymers and Materials) lead by Prof. Horst Vogel in EPFL. So far as I know, H.V. initiated this tradition almost 20 years ago, while this time the purpose of setting it up is mainly for seeking collaborations among attending groups to apply newly developed tools to investigate and answer biomedical problems.

This year’s winter school started with the evening session on 26th from the introduction of NK cells by Prof. Petter Höglund in Sweden, followed up by Prof. Werner Held in Lausanne and Prof. Daniel M Davis in London who are also working in immunology related fields. Being in Karolinska Institute where NK cell is first discovered,  Petter pioneered in a vast range of studies in understanding of NK cell functionality (sorry for not mentioning any details of his studies, but trust me that he is recognized as a very good scientist if not the best in the field).  Werner, also considered as a immunologist,  is the first one to verify the existence and the functional role of cis interaction of Ly49 A inhibitory receptor to the MHC class I molecule on the NK cell itself [Doucey, M., Scarpellino, L., Zimmer, J., Guillaume, P., Luescher, I., Bron, C., & Held, W. (2004). Cis association of Ly49A with MHC class I restricts natural killer cell inhibition Nature Immunology, 5 (3), 328-336 DOI: 10.1038/ni1043]. The direct consequence of this is that less inhibitory receptors would be left to allow binding of MHC molecules on the target cells, thus less inhibitory signals can be generated and therefore killing can be initiated, though the expression level of MHC molecules on the target may be normal. Dan, in my view, is a biophysicist who applies various of microscopic tools to investigate immune synapse (when I wrote this article, I started to look for some of his information and his educational background actually support my opinion formed at the first sight).  He is probably the first one to take seriously the nanotubes developed by NK cells to their targets, though he might not be the first one to have seen the phenomenon. The interesting thing is that NK cells extend some nanotubes (one may think of these nanotubes as extension of cell membrane or cytoskeleton) to reach the target cells which are probably a bit far away from the NK cells. Funny enough is that the NK cells try to drag the targets towards themselves while or course the targets always want to run away. The biological roles of developing these nanotubes is still vaguely understood. It is nevertheless eye-catching.

27th, the second day of the winter school, there were some people talking about odorant receptors. Not super interesting to me. It is however intriguing to know how fast some people respond to the most state-of-the-art experimental tools. There are already quite some people applying super resolution microscopic tools to tackle biological problems, namely PALM, STORM and structured illumination developed in the US and STED invented by Stefan W Hell in Göttingen. For instance, Dan’s group is applying all these techniques to study immunosynapses. Horst is also establishing PLAM/STORM in his lab. Since most of the research activities from Horst’s  group are centered around odorant receptors, I assume the use of such super-resolution-microscopy is no exception. I may not skip mentioning that I am very deeply impressed by the vast knowledge of Prof. Horst Vogel.  It is hard for anyone to overlook how many advanced techniques have been applied to biological studies in his lab, and to not be amazed by the level of his lab can maintain in each aspect. His lab activities, as a perfect example, reflect the trend of grater impact that physical and chemical methodologies can offer to biological investigations. And of course, it is by no means a singularity (I am not talking about gravitational singularity, so don’t make me wrong) in geographic distribution of science or in history . Go back to the winter school. During the evening session, my supervisor Prof. Jerker Widengren gave an overview of the activities in our lab. He started from the basic introduction of fluorescence, went to FCS, and newly established modulation excitation method to monitor the populations of different energy states of the fluorophores built up from ground state upon laser excitation, and how to use so-obtained information to gain information about how molecules interact with the local environment [Sande?n, T., Persson, G., & Widengren, J. (2008). Transient State Imaging for Microenvironmental Monitoring by Laser Scanning Microscopy Analytical Chemistry, 80 (24), 9589-9596 DOI: 10.1021/ac8018735], and he also mentioned about other activities, like applying STED imaging along with single molecule multi-parameter spectroscopy and other methods to do early diagnosis of cancer, applying FCCS to study biomolecular interactions to gain quantitative information about how NK cells regulate their killing, etc.

On 28th, the third day, the morning session started from my introduction of inverse fluorescence correlation spectroscopy (IFCS) [Stefan Wennmalm, etc., Inverse-Fluorescence Correlation Spectroscopy. Anal. Chem., 2009, 81 (22), pp 9209-9215.] (for which, I was a coauthor.) I paused for quite a while at the beginning leaving the room  freakishly silent because I was a bit too nervous to think. It was good that it went well after I passed the phase of being absent of my mind.  For people who are not familiar with the principle of IFCS, I should say in contrary to look at bursts of fluorescence intensities when fluorophore diffuse through the focal volume, we look at sudden drop of intensities when dark particles pass through a highly fluorescent background (generated by high concentration of dyes), and therefore molecules under scrutiny no longer needs to be labeled. Tor Sandén, originally from our lab, and currently a postdoc in Horst’s lab, extended this method to allow detection of non-labeled particles down to 10 nm in diameter, and he gave a presentation of his work on the last day of the winter school. On the same day of my presentation, Sofia Johansson and Johan Strömqvist from our lab talked about the NK cell project which I had participated partly. Though this research mainly addresses quantitative understanding of NK cell functionality of regulating its molecular binding pattern, they (actually solely by Johan) also patched the lack of mathematical description of non-perfectly overlapping foci which was usually the case but largely ignored by the FCCS community, which as a result introduced error in interpreting the co-diffusion of different color-labeled species. Evangelos Sisamakis also from our group introduced the concept of single molecule multi-parameter spectroscopy which allow single molecule FRET and FCS measurements.

The evening session on 28th gave me a surprise. Prof. Detlev Schild from Göttingen presented a wonderful talk. What he presented is mainly from a recent publication of his group, Junek, S., Chen, T., Alevra, M., & Schild, D. (2009). Activity Correlation Imaging: Visualizing Function and Structure of Neuronal Populations Biophysical Journal, 96 (9), 3801-3809 DOI: 10.1016/j.bpj.2008.12.3962. I am amazed by the idea of their applying online correlation calculation of temporal fluctuation of fluorescent intensities in each pixel of the recorded image to trace Ca2+ flow in individual neurons. Due to the fact that each neural cell possess different patterns of temporal fluorescence intensity fluctuation of Ca2+ sensitive dye, they were able to assign different artificial colors to different neurons. Nevertheless, the networking of different neurons is also possible to be provided by correlating the intensity fluctuations in different pixels. The correlation maps can provide the details of the fine structures of neural dendrites which were vaguely (actually not) visible in correspondent intensity images. Their line scanning microscope (in contrary to confocal microscopy which only allows point scanning ) is also very fast to acquire a 3D image of the neuronal network. It is truly a beautiful work, and deserves a more thorough introduction. I am thinking of writing another blog article about this work.

29th, it was the day to departure. But of course it does not mean there weren’t any interesting talks on that day.  My colleague, Evangelos is very much fascinated by Horst’s group combining multiple optical trapping and microfluidic device to isolate cells and study their responses to different triggers carried along with the laminar flows in different islets in the same microfluidic device without interfering each other due to the unmixing property of laminar flow.