Hi Xin-Hua,

Chemotaxis is a type of cell motility. Polarization is a shape 
measurement. These may be correlated at times, or not.

For chemotaxis, the simplest case is a stable gradient, imaged over 
tens of minutes, at low magnification (and for Dicty, low but not 
very low cell density since cells can secrete attractants and also 
produce enzymes that degrade the attractants). If you also want to 
measure cell shape, you want a reasonably high numerical aperture 
objective lens (and condenser!) and appropriate magnification onto 
the detector. For example, a typical 10x/0.3 NA objective lens 
projecting a 1x1 mm area onto a 1,000x1,000 pixel detector is at 
about the optical resolution limit [ 1.22 *  lambda / (NAobj + 
NAcond) ] of 1.0 um (but to use the resolution need to 3x 
oversample). 1.0 um pixel size is ok if you are comparing a 
population of cells that are 20 um long to a population that is 7 um long.

Stable gradients can be generated in Zigmond chamber, Dunn chamber, a 
micropipet, and other methods in the literature.

If you are acquiring timelapse images, see Futrelle et al 1982 J Cell 
Biol for a nice chemotaxis index parameter.

George
p.s. recent papers show Dicty amebae tend to alternate between left 
and right protrusions from the leading pseudopod. Acquire for long 
enough time that this does not matter.


At 03:35 PM 11/4/2009, you wrote:
>Hi, dear all,
>Since I joined Dicty community, I encountered a lot of technique 
>problems or confusions. Some of them may be not a real problem, and 
>the question may be stupid, but they all bother me for a long time. 
>I put them all here, hope you can help me clarify them.
>
>5.      Chemotaxis: to show a mutant strain has chemotaxis defect, 
>we would quantify the chemotaxis speed and directionality. However, 
>chemotaxis is also dependent on how cells are polarized. For 
>example, pi3k- cells would not show a lot of chemotaxis defect if 
>they are pulsed long enough. The thing is "pulsed enough" or 
>"polarized well" is an arbitrary concept. If polarizing is not 
>paralleling, how meaningful to calculate the absolute number of 
>"chemotaxis index"? At least we should not expect to get the same 
>number from different labs, right?
>
>Thanks,       Xin-Hua Liao


George McNamara, Ph.D.
Image Core Manager
Analytical Imaging Core Facility
University of Miami, Miller School of Medicine
Miami, FL 33136
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305-243-8436 office
http://www.sylvester.org/AICF (Analytical Imaging Core Facility)
http://www.sylvester.org/AICF/pubspectra.zip (the entire 2000+ 
spectra .xlsx file is in the zip file)
http://home.earthlink.net/~geomcnamara