I need to look at live cell morphology deformation over the course of a few hours. What sort of membrane dye would be useful for this?
Lipophilic cyanine dyes, such as DiI (Cat. No. D282), DiO (Cat. No. D275), DiD (Cat. No. D7757) or DiR (Cat. No. D12731), are commonly used. The longer the alkyl chain on the dye, the better the retention in lipophilic environments.
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Why do I lose all signal from my neuronal tracer when I do a methanol fixation on my cells?
If the tracer you chose is a lipophilic dye and fix with methanol, the lipids are lost with the methanol. If you have to use methanol fixation then choose a tracer that will covalently bind to proteins in the neurons.
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I stained my cells with a lipophilic cyanine dye, like DiI, but the signal was lost when I tried to follow up with antibody labeling. Why?
Since these dyes insert into lipid membranes, any disruption of the membranes leads to loss of the dye. This includes permeabilization with detergents like Triton X-100 or organic solvents like methanol. Permeabilization is necessary for intracellular antibody labeling, leading to loss of the dye. Instead, a reactive dye such as CFDA SE should be used to allow for covalent attachment to cellular components, thus providing for better retention upon fixation and permeabilization.
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I labeled my neurons with DiI and then fixed and permeabilized and now I have no signal. What did I do wrong?
DiI is a lipophilic dye that resides mostly in lipids in the cell, when cells are permeabilized with detergent or fixed using alcohol this strips away the lipid and the dye. If permeabilization is required CM-DiI can be used because this binds covalently to proteins in the membrane; some signal is lost upon fixation/permeabilization, but enough signal should be retained to make detection possible.
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How long does it take for lipophlic tracers to transport along the membrane? How much faster are the FAST lipophilic dyes?
The transport is fairly slow, around 6 mm/day in live tissue and slower in fixed tissue, so diffusion of lipophilic carbocyanine tracers from the point of their application to the terminus of a neuron can take several days to weeks The FAST DiO and DiI analogs (which have unsaturated alkyl tails) can improve transport rate by around 50%.
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