Определение липидного плота разделов флуоресцентно с метками зонды в живых клетках при флуоресцентной спектроскопии корреляции (FCS)
Summary
Техника для исследования разделов липидного плота флуоресцентных белков в мембране живой клетки описывается. Он использует различия в диффузии время белки, расположенные внутри или за пределами липидного плоты. Приобретение может осуществляться динамически в контрольных условиях или после наркомании.
Abstract
In the past fifteen years the notion that cell membranes are not homogenous and rely on microdomains to exert their functions has become widely accepted. Lipid rafts are membrane microdomains enriched in cholesterol and sphingolipids. They play a role in cellular physiological processes such as signalling, and trafficking1,2 but are also thought to be key players in several diseases including viral or bacterial infections and neurodegenerative diseases3.
Yet their existence is still a matter of controversy4,5. Indeed, lipid raft size has been estimated to be around 20 nm6, far under the resolution limit of conventional microscopy (around 200 nm), thus precluding their direct imaging. Up to now, the main techniques used to assess the partition of proteins of interest inside lipid rafts were Detergent Resistant Membranes (DRMs) isolation and co-patching with antibodies. Though widely used because of their rather easy implementation, these techniques were prone to artefacts and thus criticized7,8. Technical improvements were therefore necessary to overcome these artefacts and to be able to probe lipid rafts partition in living cells.
Here we present a method for the sensitive analysis of lipid rafts partition of fluorescently-tagged proteins or lipids in the plasma membrane of living cells. This method, termed Fluorescence Correlation Spectroscopy (FCS), relies on the disparity in diffusion times of fluorescent probes located inside or outside of lipid rafts. In fact, as evidenced in both artificial membranes and cell cultures, probes would diffuse much faster outside than inside dense lipid rafts9,10. To determine diffusion times, minute fluorescence fluctuations are measured as a function of time in a focal volume (approximately 1 femtoliter), located at the plasma membrane of cells with a confocal microscope (Fig. 1). The auto-correlation curves can then be drawn from these fluctuations and fitted with appropriate mathematical diffusion models11.
FCS can be used to determine the lipid raft partitioning of various probes, as long as they are fluorescently tagged. Fluorescent tagging can be achieved by expression of fluorescent fusion proteins or by binding of fluorescent ligands. Moreover, FCS can be used not only in artificial membranes and cell lines but also in primary cultures, as described recently12. It can also be used to follow the dynamics of lipid raft partitioning after drug addition or membrane lipid composition change12.
Protocol
Discussion
Метод ФТС представленные здесь позволяет чувствительный и быстрый анализ разделов липидного плота флуоресцентных зондов интерес в живых клетках. ФТС сочетает в себе точность локализации конфокальной микроскопии с чувствительностью одного счета фотонов. Основное различие между ФТС …
Divulgations
The authors have nothing to disclose.
Acknowledgements
Эта работа была поддержана грантом Agence Nationale-де-ла Recherche (ChoAD). Мы также благодарны Фонду ICM (институт дю Cerveau и др. де-ла-Moelle) за их финансовую поддержку.
Materials
| Name of the reagent | Company | Catalogue number | Comments |
| Cholera toxin subunit B-Alexa 488 | Invitrogen | C-34775 | MW (pentamer) = 57 kg/mol |
| Confocal microscope | Leica | SP5 | |
| Incubator for temperature and CO2 control | Life imaging services | The Cube and the Box | |
| SPAD (Single Photon Avalanche Diode) | MPD (Micro Photon Devices) | PDM serie (100 μm sensitive area) | |
| High pass 488 nm filter | Semrock | 488 nm blocking edge BrightLine long-pass filter Part # FF01-488/LP-25 |
|
| FCS detection unit | Picoquant | Picoharp 300 module | |
| Acquisition and auto-correlation software | Picoquant | SymPhoTime | |
| Fitting software | OriginLab | OriginPro8 |
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